Hi All
Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
Mark

Mark

Don't give up. There are other things you can do. If you have an oscilloscope check signals through video amplifiers. You could feed in a video signal from a VCR. This will give a known signal. I posted more on the other thread.

Norm

:Hi All
: Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
:Mark
:

:Mark
:
: Don't give up. There are other things you can do. If you have an oscilloscope check signals through video amplifiers. You could feed in a video signal from a VCR. This will give a known signal. I posted more on the other thread.
:
:Norm
:Hi Norm
Well I've done signal tracing and from what I can tell no positive results, in other words things appear too be right signal wise and level wise, I further did resistance checks on the pins of the CRT and again they were where they should be, the strange thing is I get good sound on the channels, but the picture is just no good, I think at this point with out anything else to check, unless you have any ideas, I'm calling it quits on this.
Mark
::Hi All
:: Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
::Mark
::

I didn't read the other thread, so please pardon my somewhat ill-informed interruption. Is the picture tube good or is it weak? Do you get a bright raster or a dim one? If the raster is dim but the contrast is fine, then your picture tube may be bad. You may want to try a picture tube brightener. This sounds bad at first, but your other option is replacing the picture tube. It is possible (or you can have it rebuilt), but it's expensive. If you cannot obtain a picture tube brightener, and the heaters are all wired in parallel, you can build a very easy to make voltage doubler, and then put a resistor on this to make the voltage across the picture tube heater about 7 or 8 volts--whichever produces fair results.....7 should be adequate. DO NOT DO THIS UNLESS YOU ARE ABSOLUTELY SURE THAT THE PICTURE TUBE IS BAD.

Thomas

Okay...I read your other post now (the entire thing). First have you replaced any resistors in the high voltage circuit? A lot of older televisions have a resistor on the high voltage rectifier (like a 1B3, 1G3 tube). In my set and many this is a 1 Meg resistor. If it drifts, the picture will be dim. Mine was dim. I replaced this resistor and what a difference! The picture will also bloom if the resistor is weak--it'll get bigger and blurry when the picture gets brighter. With old televisions like yours this will happen anyway, but not as much. My television is also old, by the way (1947 DeWald BT-100....RCA 630TS chassis).

Also, have you done any wiring with the tube socket? I realize that things can happen that I've never seen before. It's not like I've seen everything there is to see. With all of the picture tubes I've seen though (probably about 20 in my life, so that isn't much), I've never seen a blue glow in the neck of the tube. If something's wired incorrectly, there'll be a high current draw in the neck, which will cause a blue glow and also a lack of a beam on the screen. Usually, though, this will ruin deflection, so it probably isn't your problem. Green is an odd color to be seen in a tube. I don't think that it's gas, but it's odd. I know that the old high vacuum Crooks tubes glowed green on the edges of the glass. Gas usually glows like a cloud, but the Crooks effect is either on the edge of the glass or on the mica supports within the tube.

Also, make sure your ion deflection magnet is installed facing the correct direction. With my television it is possible to get some sort of picture with the ion magnet installed facing backwards. Some wonderful person scribed an arrow on it a long time ago, though, so this helps me. Also, on mine one of the retaining bands is blue and the other is black. This helps with orientation if I can remember which way they were to begin with (assuming that this was the correct way).

Also regarding the ion magnet, your focus coil can have a big affect on how the ion magnet performs. Moving the focussing coil can make it necessary to readjust the ion magnet. If you can focus the picture and get it to fill the screen, though, then you should be able to get the ion trap magnet to perform properly. (This is per my experience with my DeWald television....doesn't necessarily mean that this experience is routine with every set of this type.)

If you are able to do a voltage check on the picture tube high voltage (this requires a special meter capable of these voltages, and this can be very dangerous to perform), is the voltage correct? The horizontal oscillator output usually controls how much voltage the flyback coil produces. If the output is low, your high voltage will be low.

Thomas

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I only see two threads relevant to the det diode topic, with no further reference relating to the
particular brand and chassis that you are working with. However, with that specific kinescope
number utilized, it would have to go back to day one of B& W televison receivers.
As for your fear of possible reverse installation of the detector diode, don't even think about it,
as any damaging effect would be negated by virtue of the miniscule 100's of millivolt levels
being involved. This not a situation like a power rectifier diode being reversed in its installation
......a la..... ka-BOOM on power up..
However, in such a situation, the one thing that would be INSTANTLY recognizable in case of a
reversed diode installation would be the reverse produced video, wherein the picture would
resemble a photographic negative. Along with an improper creation of sync with an adjunct
tearing, bending and fluttering of the resultant picture being created.
Sould your test equipment access include an audio generator it would be possible to start
at the kine cathode/or/1st grid (I don't know your model...to schema reference...so, almost
universally the 1st grid where video drive is injected). There you would inject, thru a .1 ufd/
400VDC paper/poly isolation capacitor, a ~400 cycle 15 VP/P sine which should swamp
the kine and produce a nice gradiated black series of hoz lines for its video display.
(Should the generator have square wave capability, switching to that signal output mode
would produce a very distinct black white transition between the lines). I still prefer the sine,
as some degree of stage gain can be discerned in the transitional shading of the pattern
from grey to black. From that point it is just a matter of working back thru the video output
plate stage and its coupling component elements and then on to the first grid stage of that
tube ( progressively decreasing signal input level as required) until a inpointing of a loss or
severe weakening of stage gain shows up.
Some sets even used a tandem of two tubes in their video output circuitry, but eventually you
should end up at the video's derivation point, the video detector diode ( The majority of sets
utilizing the then popular 1N60 series of "geranium" diodes). Two other common things to
watch for would be a contrast control problem or an aged / dried out / low capacitance cathode
bypass electrolytic capacitor.
This signal injecton technique should present you with a sledge hammer to tack hammer signal
variance in troubleshooting of even the worse of video conditions.
Sir Norms extraction of raw composite video from a VCR'uh's back RCA jack ( Still utilizing
the isolation capacitor for injection) should suffice if you had a modicum of video gain through
lower level stages.
However, nowadays, my preference is the utilization of a Video DVD player, they almost
universally generate an internal ROM accessed test pattern (manufacturers propoganda
oriented) the instant the unit is powered up from out of standby. No DVD being required, until
the point whereyou really want / need to evaluate with some changing video.

73's de Edd

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

:Hi All
: Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
:Mark
:

:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:I only see two threads relevant to the det diode topic, with no further reference relating to the
:particular brand and chassis that you are working with. However, with that specific kinescope
:number utilized, it would have to go back to day one of B& W televison receivers.
:As for your fear of possible reverse installation of the detector diode, don't even think about it,
:as any damaging effect would be negated by virtue of the miniscule 100's of millivolt levels
:being involved. This not a situation like a power rectifier diode being reversed in its installation
:......a la..... ka-BOOM on power up..
:However, in such a situation, the one thing that would be INSTANTLY recognizable in case of a
:reversed diode installation would be the reverse produced video, wherein the picture would
:resemble a photographic negative. Along with an improper creation of sync with an adjunct
:tearing, bending and fluttering of the resultant picture being created.
:Sould your test equipment access include an audio generator it would be possible to start
:at the kine cathode/or/1st grid (I don't know your model...to schema reference...so, almost
:universally the 1st grid where video drive is injected). There you would inject, thru a .1 ufd/
:400VDC paper/poly isolation capacitor, a ~400 cycle 15 VP/P sine which should swamp
:the kine and produce a nice gradiated black series of hoz lines for its video display.
:(Should the generator have square wave capability, switching to that signal output mode
:would produce a very distinct black white transition between the lines). I still prefer the sine,
:as some degree of stage gain can be discerned in the transitional shading of the pattern
:from grey to black. From that point it is just a matter of working back thru the video output
:plate stage and its coupling component elements and then on to the first grid stage of that
:tube ( progressively decreasing signal input level as required) until a inpointing of a loss or
:severe weakening of stage gain shows up.
:Some sets even used a tandem of two tubes in their video output circuitry, but eventually you
:should end up at the video's derivation point, the video detector diode ( The majority of sets
:utilizing the then popular 1N60 series of "geranium" diodes). Two other common things to
:watch for would be a contrast control problem or an aged / dried out / low capacitance cathode
:bypass electrolytic capacitor.
:This signal injecton technique should present you with a sledge hammer to tack hammer signal
:variance in troubleshooting of even the worse of video conditions.
:Sir Norms extraction of raw composite video from a VCR'uh's back RCA jack ( Still utilizing
:the isolation capacitor for injection) should suffice if you had a modicum of video gain through
:lower level stages.
:However, nowadays, my preference is the utilization of a Video DVD player, they almost
:universally generate an internal ROM accessed test pattern (manufacturers propoganda
:oriented) the instant the unit is powered up from out of standby. No DVD being required, until
:the point whereyou really want / need to evaluate with some changing video.
:
:73's de Edd
:
:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:
::Hi All
:: Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
::Mark
::Hi Edd
Thank you so much for the very detailed info, this is what I've been hoping someone would reply with, you have given me a very good idea as too what might be going on, I'm printing off this page for refernence, the model I'm working with is a Zenith G2322, not sure of the chassis # off hand, but if you would like I can send you a copy of the SAMS schematic I have for it, let me know, in the mean time I'm taking you advice to heart, thank you so much! sounds like you really know these old TV's:)
Mark

::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::I only see two threads relevant to the det diode topic, with no further reference relating to the
::particular brand and chassis that you are working with. However, with that specific kinescope
::number utilized, it would have to go back to day one of B& W televison receivers.
::As for your fear of possible reverse installation of the detector diode, don't even think about it,
::as any damaging effect would be negated by virtue of the miniscule 100's of millivolt levels
::being involved. This not a situation like a power rectifier diode being reversed in its installation
::......a la..... ka-BOOM on power up..
::However, in such a situation, the one thing that would be INSTANTLY recognizable in case of a
::reversed diode installation would be the reverse produced video, wherein the picture would
::resemble a photographic negative. Along with an improper creation of sync with an adjunct
::tearing, bending and fluttering of the resultant picture being created.
::Sould your test equipment access include an audio generator it would be possible to start
::at the kine cathode/or/1st grid (I don't know your model...to schema reference...so, almost
::universally the 1st grid where video drive is injected). There you would inject, thru a .1 ufd/
::400VDC paper/poly isolation capacitor, a ~400 cycle 15 VP/P sine which should swamp
::the kine and produce a nice gradiated black series of hoz lines for its video display.
::(Should the generator have square wave capability, switching to that signal output mode
::would produce a very distinct black white transition between the lines). I still prefer the sine,
::as some degree of stage gain can be discerned in the transitional shading of the pattern
::from grey to black. From that point it is just a matter of working back thru the video output
::plate stage and its coupling component elements and then on to the first grid stage of that
::tube ( progressively decreasing signal input level as required) until a inpointing of a loss or
::severe weakening of stage gain shows up.
::Some sets even used a tandem of two tubes in their video output circuitry, but eventually you
::should end up at the video's derivation point, the video detector diode ( The majority of sets
::utilizing the then popular 1N60 series of "geranium" diodes). Two other common things to
::watch for would be a contrast control problem or an aged / dried out / low capacitance cathode
::bypass electrolytic capacitor.
::This signal injecton technique should present you with a sledge hammer to tack hammer signal
::variance in troubleshooting of even the worse of video conditions.
::Sir Norms extraction of raw composite video from a VCR'uh's back RCA jack ( Still utilizing
::the isolation capacitor for injection) should suffice if you had a modicum of video gain through
::lower level stages.
::However, nowadays, my preference is the utilization of a Video DVD player, they almost
::universally generate an internal ROM accessed test pattern (manufacturers propoganda
::oriented) the instant the unit is powered up from out of standby. No DVD being required, until
::the point whereyou really want / need to evaluate with some changing video.
::
::73's de Edd
::
::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::
:::Hi All
::: Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
:::Mark
:::Hi Edd
: Thank you so much for the very detailed info, this is what I've been hoping someone would reply with, you have given me a very good idea as too what might be going on, I'm printing off this page for refernence, the model I'm working with is a Zenith G2322, not sure of the chassis # off hand, but if you would like I can send you a copy of the SAMS schematic I have for it, let me know, in the mean time I'm taking you advice to heart, thank you so much! sounds like you really know these old TV's:)
:Mark
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Rgr….Rgr…. Take the info that I have supplied and proceed, considering that you have access to an AF audio sig generator…in the interim I will dig deeeeeeep into the “Dust Bin” ....may take awhile...and extract Sir Samuels Folder 98 # 17 and research the circuitry to further refine the troubleshooting technique specific to that chassis....
73’s de Edd
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

:::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:::I only see two threads relevant to the det diode topic, with no further reference relating to the
:::particular brand and chassis that you are working with. However, with that specific kinescope
:::number utilized, it would have to go back to day one of B& W televison receivers.
:::As for your fear of possible reverse installation of the detector diode, don't even think about it,
:::as any damaging effect would be negated by virtue of the miniscule 100's of millivolt levels
:::being involved. This not a situation like a power rectifier diode being reversed in its installation
:::......a la..... ka-BOOM on power up..
:::However, in such a situation, the one thing that would be INSTANTLY recognizable in case of a
:::reversed diode installation would be the reverse produced video, wherein the picture would
:::resemble a photographic negative. Along with an improper creation of sync with an adjunct
:::tearing, bending and fluttering of the resultant picture being created.
:::Sould your test equipment access include an audio generator it would be possible to start
:::at the kine cathode/or/1st grid (I don't know your model...to schema reference...so, almost
:::universally the 1st grid where video drive is injected). There you would inject, thru a .1 ufd/
:::400VDC paper/poly isolation capacitor, a ~400 cycle 15 VP/P sine which should swamp
:::the kine and produce a nice gradiated black series of hoz lines for its video display.
:::(Should the generator have square wave capability, switching to that signal output mode
:::would produce a very distinct black white transition between the lines). I still prefer the sine,
:::as some degree of stage gain can be discerned in the transitional shading of the pattern
:::from grey to black. From that point it is just a matter of working back thru the video output
:::plate stage and its coupling component elements and then on to the first grid stage of that
:::tube ( progressively decreasing signal input level as required) until a inpointing of a loss or
:::severe weakening of stage gain shows up.
:::Some sets even used a tandem of two tubes in their video output circuitry, but eventually you
:::should end up at the video's derivation point, the video detector diode ( The majority of sets
:::utilizing the then popular 1N60 series of "geranium" diodes). Two other common things to
:::watch for would be a contrast control problem or an aged / dried out / low capacitance cathode
:::bypass electrolytic capacitor.
:::This signal injecton technique should present you with a sledge hammer to tack hammer signal
:::variance in troubleshooting of even the worse of video conditions.
:::Sir Norms extraction of raw composite video from a VCR'uh's back RCA jack ( Still utilizing
:::the isolation capacitor for injection) should suffice if you had a modicum of video gain through
:::lower level stages.
:::However, nowadays, my preference is the utilization of a Video DVD player, they almost
:::universally generate an internal ROM accessed test pattern (manufacturers propoganda
:::oriented) the instant the unit is powered up from out of standby. No DVD being required, until
:::the point whereyou really want / need to evaluate with some changing video.
:::
:::73's de Edd
:::
:::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:::
::::Hi All
:::: Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
::::Mark
::::Hi Edd
:: Thank you so much for the very detailed info, this is what I've been hoping someone would reply with, you have given me a very good idea as too what might be going on, I'm printing off this page for refernence, the model I'm working with is a Zenith G2322, not sure of the chassis # off hand, but if you would like I can send you a copy of the SAMS schematic I have for it, let me know, in the mean time I'm taking you advice to heart, thank you so much! sounds like you really know these old TV's:)
::Mark
:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:Rgr….Rgr…. Take the info that I have supplied and proceed, considering that you have access to an AF audio sig generator…in the interim I will dig deeeeeeep into the “Dust Bin” ....may take awhile...and extract Sir Samuels Folder 98 # 17 and research the circuitry to further refine the troubleshooting technique specific to that chassis....
:73’s de Edd
:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Hi Edd
Will do, I have also replaced the contrast control, just on an outside chance, also I must tell you I have in the past tence already gone through and replaced all capacitors and resistors that were bad or way out of tolerance, let me know if you find this SAMS and any other info relating to this problem will be greatly appreciated:)
Mark

::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::::I only see two threads relevant to the det diode topic, with no further reference relating to the
::::particular brand and chassis that you are working with. However, with that specific kinescope
::::number utilized, it would have to go back to day one of B& W televison receivers.
::::As for your fear of possible reverse installation of the detector diode, don't even think about it,
::::as any damaging effect would be negated by virtue of the miniscule 100's of millivolt levels
::::being involved. This not a situation like a power rectifier diode being reversed in its installation
::::......a la..... ka-BOOM on power up..
::::However, in such a situation, the one thing that would be INSTANTLY recognizable in case of a
::::reversed diode installation would be the reverse produced video, wherein the picture would
::::resemble a photographic negative. Along with an improper creation of sync with an adjunct
::::tearing, bending and fluttering of the resultant picture being created.
::::Sould your test equipment access include an audio generator it would be possible to start
::::at the kine cathode/or/1st grid (I don't know your model...to schema reference...so, almost
::::universally the 1st grid where video drive is injected). There you would inject, thru a .1 ufd/
::::400VDC paper/poly isolation capacitor, a ~400 cycle 15 VP/P sine which should swamp
::::the kine and produce a nice gradiated black series of hoz lines for its video display.
::::(Should the generator have square wave capability, switching to that signal output mode
::::would produce a very distinct black white transition between the lines). I still prefer the sine,
::::as some degree of stage gain can be discerned in the transitional shading of the pattern
::::from grey to black. From that point it is just a matter of working back thru the video output
::::plate stage and its coupling component elements and then on to the first grid stage of that
::::tube ( progressively decreasing signal input level as required) until a inpointing of a loss or
::::severe weakening of stage gain shows up.
::::Some sets even used a tandem of two tubes in their video output circuitry, but eventually you
::::should end up at the video's derivation point, the video detector diode ( The majority of sets
::::utilizing the then popular 1N60 series of "geranium" diodes). Two other common things to
::::watch for would be a contrast control problem or an aged / dried out / low capacitance cathode
::::bypass electrolytic capacitor.
::::This signal injecton technique should present you with a sledge hammer to tack hammer signal
::::variance in troubleshooting of even the worse of video conditions.
::::Sir Norms extraction of raw composite video from a VCR'uh's back RCA jack ( Still utilizing
::::the isolation capacitor for injection) should suffice if you had a modicum of video gain through
::::lower level stages.
::::However, nowadays, my preference is the utilization of a Video DVD player, they almost
::::universally generate an internal ROM accessed test pattern (manufacturers propoganda
::::oriented) the instant the unit is powered up from out of standby. No DVD being required, until
::::the point whereyou really want / need to evaluate with some changing video.
::::
::::73's de Edd
::::
::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::::
:::::Hi All
::::: Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
:::::Mark
:::::Hi Edd
::: Thank you so much for the very detailed info, this is what I've been hoping someone would reply with, you have given me a very good idea as too what might be going on, I'm printing off this page for refernence, the model I'm working with is a Zenith G2322, not sure of the chassis # off hand, but if you would like I can send you a copy of the SAMS schematic I have for it, let me know, in the mean time I'm taking you advice to heart, thank you so much! sounds like you really know these old TV's:)
:::Mark
::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::Rgr….Rgr…. Take the info that I have supplied and proceed, considering that you have access to an AF audio sig generator…in the interim I will dig deeeeeeep into the “Dust Bin” ....may take awhile...and extract Sir Samuels Folder 98 # 17 and research the circuitry to further refine the troubleshooting technique specific to that chassis....
::73’s de Edd
::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Hi Edd
: Will do, I have also replaced the contrast control, just on an outside chance, also I must tell you I have in the past tence already gone through and replaced all capacitors and resistors that were bad or way out of tolerance, let me know if you find this SAMS and any other info relating to this problem will be greatly appreciated:)
:Mark
:Hi Edd
I have discovered a problem in doing what you state, there is a harness that connects between the TV Chassis and the Radio, when disconnected and the TV chassis is out of the cabinet, I cannot power up the TV chassis by itself, I'm not sure, but would assume way back when, they must have had a dummy plug they connected too this harness in order to work on the TV chassis by itself, stand alone, out of the cabinet, maybe you can enlighten me as too how too go about this so I can make the test you state in the previous, let me know, thanks:)
Mark

:::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:::::I only see two threads relevant to the det diode topic, with no further reference relating to the
:::::particular brand and chassis that you are working with. However, with that specific kinescope
:::::number utilized, it would have to go back to day one of B& W televison receivers.
:::::As for your fear of possible reverse installation of the detector diode, don't even think about it,
:::::as any damaging effect would be negated by virtue of the miniscule 100's of millivolt levels
:::::being involved. This not a situation like a power rectifier diode being reversed in its installation
:::::......a la..... ka-BOOM on power up..
:::::However, in such a situation, the one thing that would be INSTANTLY recognizable in case of a
:::::reversed diode installation would be the reverse produced video, wherein the picture would
:::::resemble a photographic negative. Along with an improper creation of sync with an adjunct
:::::tearing, bending and fluttering of the resultant picture being created.
:::::Sould your test equipment access include an audio generator it would be possible to start
:::::at the kine cathode/or/1st grid (I don't know your model...to schema reference...so, almost
:::::universally the 1st grid where video drive is injected). There you would inject, thru a .1 ufd/
:::::400VDC paper/poly isolation capacitor, a ~400 cycle 15 VP/P sine which should swamp
:::::the kine and produce a nice gradiated black series of hoz lines for its video display.
:::::(Should the generator have square wave capability, switching to that signal output mode
:::::would produce a very distinct black white transition between the lines). I still prefer the sine,
:::::as some degree of stage gain can be discerned in the transitional shading of the pattern
:::::from grey to black. From that point it is just a matter of working back thru the video output
:::::plate stage and its coupling component elements and then on to the first grid stage of that
:::::tube ( progressively decreasing signal input level as required) until a inpointing of a loss or
:::::severe weakening of stage gain shows up.
:::::Some sets even used a tandem of two tubes in their video output circuitry, but eventually you
:::::should end up at the video's derivation point, the video detector diode ( The majority of sets
:::::utilizing the then popular 1N60 series of "geranium" diodes). Two other common things to
:::::watch for would be a contrast control problem or an aged / dried out / low capacitance cathode
:::::bypass electrolytic capacitor.
:::::This signal injecton technique should present you with a sledge hammer to tack hammer signal
:::::variance in troubleshooting of even the worse of video conditions.
:::::Sir Norms extraction of raw composite video from a VCR'uh's back RCA jack ( Still utilizing
:::::the isolation capacitor for injection) should suffice if you had a modicum of video gain through
:::::lower level stages.
:::::However, nowadays, my preference is the utilization of a Video DVD player, they almost
:::::universally generate an internal ROM accessed test pattern (manufacturers propoganda
:::::oriented) the instant the unit is powered up from out of standby. No DVD being required, until
:::::the point whereyou really want / need to evaluate with some changing video.
:::::
:::::73's de Edd
:::::
:::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:::::
::::::Hi All
:::::: Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
::::::Mark
::::::Hi Edd
:::: Thank you so much for the very detailed info, this is what I've been hoping someone would reply with, you have given me a very good idea as too what might be going on, I'm printing off this page for refernence, the model I'm working with is a Zenith G2322, not sure of the chassis # off hand, but if you would like I can send you a copy of the SAMS schematic I have for it, let me know, in the mean time I'm taking you advice to heart, thank you so much! sounds like you really know these old TV's:)
::::Mark
:::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:::Rgr….Rgr…. Take the info that I have supplied and proceed, considering that you have access to an AF audio sig generator…in the interim I will dig deeeeeeep into the “Dust Bin” ....may take awhile...and extract Sir Samuels Folder 98 # 17 and research the circuitry to further refine the troubleshooting technique specific to that chassis....
:::73’s de Edd
:::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Hi Edd
:: Will do, I have also replaced the contrast control, just on an outside chance, also I must tell you I have in the past tence already gone through and replaced all capacitors and resistors that were bad or way out of tolerance, let me know if you find this SAMS and any other info relating to this problem will be greatly appreciated:)
::Mark
::Hi Edd
: I have discovered a problem in doing what you state, there is a harness that connects between the TV Chassis and the Radio, when disconnected and the TV chassis is out of the cabinet, I cannot power up the TV chassis by itself, I'm not sure, but would assume way back when, they must have had a dummy plug they connected too this harness in order to work on the TV chassis by itself, stand alone, out of the cabinet, maybe you can enlighten me as too how too go about this so I can make the test you state in the previous, let me know, thanks:)
:Mark

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Initially, in responding to your octal chassis-interconnecting plug. I always liked to take readings from the top...especially with that cumbersome pic tube weight also being considered. You might possibly have some of the mini 7-9 pin adapter sockets to plug a tube into and then be able to have topside access to the test tabs that are arranged around that unit's top periphery. If not then take a short length of #26 insulated solid wire (Freebie....100 pair telephone trunk line wire..or also... common Telco attic wiring) and bare 1/4 in on each end. One end is twirled 3 times around the tube pin(s) concerned...easy with surgical tweezers.......then press them in against the glass end. The wire is then dressed up vertically to the tube side so that the other bared end is accessible for metering / sig injection / sig access. This technique doesn't fly at the RF strata...but we're only into audio and the video spectrum.... so it will be permissible.
OK, I now have the schematic in hand and looks like your video section is processed thru two triode sections of a 12AU7 schematically assigned as V8 . Initially take a voltage reading of pin 1 at ~110 Vdc, pin3 at ~1 Vdc, pin 6 at ~330 Vdc and pin 8 at ~18Vdc. If those are in the ballpark move on to look at the schema where you will see the 1N64 det diode...as prophesized... series feeding thru L10 then L11 coils and on into the 1st grid of V8a pin 2. At this same point a reference is also fed down to the V9 AGC triode. At this time get your best picture possible on the set and then move down and find R134....your sets AGC control. Take a fine point blue Sharpie and make a reference "tick" mark on both the shaft and its adjunct collar so that the control could precisely be reset to its initial position if required. Now, adjusting the control should result in producing a progressively weaker and washed out gray picture in one direction, while the other direction should produce a more contrasty video and then the pic will overload and start producing a tearing, out of sync picture. Typically the control is properly adjusted by being just back from that instability threshold back to where a stable contrasty picture is acquired on the strongest station to be received. That adjustment could possibly even be your sole contrast/ weak video problem, had it been misadjusted by a prior, unknowledgeable person in turning all the set controls helter-skelter.
That possibility covered, we are now considering the plate signal of V8a where the sound info is extracted via tranfo L15, and you are saying that the sound is strong and clear. Considering that we will assume that stage as being OK. Video is then fed into the 1st grid stage of V8b. Note the cathode...pin 8...is bypassed with C2 "D" section of a canned electrolytic, if that cap is bad you will be getting no contrast..Low Freq gain thru that stage...and a washed out picture and minimal contrast control action. I like to see that unit be replaced with a modern axial / radial leaded 47 ufd 25 WVDC single unit, right across its R 50 (680 ohm) shunting resistor. The next place of interest would be the companion plate circuitry of V8b at pin 6 where series wired peaking coil L13 and plate load inductor L14 reside. Coils in the video amp circuitry are abject to failures, particularly in the fine ga wire that is wound upon forms (sometimes , a resistors body)
On this particular chassis check L10, L12, and L13 and see if they fall in that category. Then, system powered down and afterburners off, check those coils resistances, they should be low coil range ohmmages vice the shunt resistor value. E.G. take L13 if it was reading 22k you would know that coil is open and that would also produce a very weak gray picture performance ..case closed. However, you really should have caught the side effect of decreased passage of supply voltage to pin 6 when measuring it back at initial voltage tests. But, as you can see, the same variants being possible at the other shunted inductors mentioned. That encompasses your complete video sequence from det to the injection to kine... pin 2.... 1st grid circuit. The cathode...pin 11... is where the sets brightness parameters are established. If brightness control range is normal, the only thing of any importance with that area being the C53 .022 ufd (no DC level leakage tolerated) cap feeding in a vert pulse from the vertical circuit for blanking out and the creation of vertical retrace blanking for the created video display.
If none of these sequences were your problem, then the injection of Audio in for a video signal is in order, as was earlier mentioned.

BTW...attached herewith is a relative reference thumbnail Zenith schema for any popcorn spectators in the peanut gallery.

Location: http://img476.imageshack.us/img476/8455/zenagcvideo22ns.jpg

73's de Edd
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

::::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::::::I only see two threads relevant to the det diode topic, with no further reference relating to the
::::::particular brand and chassis that you are working with. However, with that specific kinescope
::::::number utilized, it would have to go back to day one of B& W televison receivers.
::::::As for your fear of possible reverse installation of the detector diode, don't even think about it,
::::::as any damaging effect would be negated by virtue of the miniscule 100's of millivolt levels
::::::being involved. This not a situation like a power rectifier diode being reversed in its installation
::::::......a la..... ka-BOOM on power up..
::::::However, in such a situation, the one thing that would be INSTANTLY recognizable in case of a
::::::reversed diode installation would be the reverse produced video, wherein the picture would
::::::resemble a photographic negative. Along with an improper creation of sync with an adjunct
::::::tearing, bending and fluttering of the resultant picture being created.
::::::Sould your test equipment access include an audio generator it would be possible to start
::::::at the kine cathode/or/1st grid (I don't know your model...to schema reference...so, almost
::::::universally the 1st grid where video drive is injected). There you would inject, thru a .1 ufd/
::::::400VDC paper/poly isolation capacitor, a ~400 cycle 15 VP/P sine which should swamp
::::::the kine and produce a nice gradiated black series of hoz lines for its video display.
::::::(Should the generator have square wave capability, switching to that signal output mode
::::::would produce a very distinct black white transition between the lines). I still prefer the sine,
::::::as some degree of stage gain can be discerned in the transitional shading of the pattern
::::::from grey to black. From that point it is just a matter of working back thru the video output
::::::plate stage and its coupling component elements and then on to the first grid stage of that
::::::tube ( progressively decreasing signal input level as required) until a inpointing of a loss or
::::::severe weakening of stage gain shows up.
::::::Some sets even used a tandem of two tubes in their video output circuitry, but eventually you
::::::should end up at the video's derivation point, the video detector diode ( The majority of sets
::::::utilizing the then popular 1N60 series of "geranium" diodes). Two other common things to
::::::watch for would be a contrast control problem or an aged / dried out / low capacitance cathode
::::::bypass electrolytic capacitor.
::::::This signal injecton technique should present you with a sledge hammer to tack hammer signal
::::::variance in troubleshooting of even the worse of video conditions.
::::::Sir Norms extraction of raw composite video from a VCR'uh's back RCA jack ( Still utilizing
::::::the isolation capacitor for injection) should suffice if you had a modicum of video gain through
::::::lower level stages.
::::::However, nowadays, my preference is the utilization of a Video DVD player, they almost
::::::universally generate an internal ROM accessed test pattern (manufacturers propoganda
::::::oriented) the instant the unit is powered up from out of standby. No DVD being required, until
::::::the point whereyou really want / need to evaluate with some changing video.
::::::
::::::73's de Edd
::::::
::::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::::::
:::::::Hi All
::::::: Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
:::::::Mark
:::::::Hi Edd
::::: Thank you so much for the very detailed info, this is what I've been hoping someone would reply with, you have given me a very good idea as too what might be going on, I'm printing off this page for refernence, the model I'm working with is a Zenith G2322, not sure of the chassis # off hand, but if you would like I can send you a copy of the SAMS schematic I have for it, let me know, in the mean time I'm taking you advice to heart, thank you so much! sounds like you really know these old TV's:)
:::::Mark
::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::::Rgr….Rgr…. Take the info that I have supplied and proceed, considering that you have access to an AF audio sig generator…in the interim I will dig deeeeeeep into the “Dust Bin” ....may take awhile...and extract Sir Samuels Folder 98 # 17 and research the circuitry to further refine the troubleshooting technique specific to that chassis....
::::73’s de Edd
::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Hi Edd
::: Will do, I have also replaced the contrast control, just on an outside chance, also I must tell you I have in the past tence already gone through and replaced all capacitors and resistors that were bad or way out of tolerance, let me know if you find this SAMS and any other info relating to this problem will be greatly appreciated:)
:::Mark
:::Hi Edd
:: I have discovered a problem in doing what you state, there is a harness that connects between the TV Chassis and the Radio, when disconnected and the TV chassis is out of the cabinet, I cannot power up the TV chassis by itself, I'm not sure, but would assume way back when, they must have had a dummy plug they connected too this harness in order to work on the TV chassis by itself, stand alone, out of the cabinet, maybe you can enlighten me as too how too go about this so I can make the test you state in the previous, let me know, thanks:)
::Mark
:
:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:
:Initially, in responding to your octal chassis-interconnecting plug. I always liked to take readings from the top...especially with that cumbersome pic tube weight also being considered. You might possibly have some of the mini 7-9 pin adapter sockets to plug a tube into and then be able to have topside access to the test tabs that are arranged around that unit's top periphery. If not then take a short length of #26 insulated solid wire (Freebie....100 pair telephone trunk line wire..or also... common Telco attic wiring) and bare 1/4 in on each end. One end is twirled 3 times around the tube pin(s) concerned...easy with surgical tweezers.......then press them in against the glass end. The wire is then dressed up vertically to the tube side so that the other bared end is accessible for metering / sig injection / sig access. This technique doesn't fly at the RF strata...but we're only into audio and the video spectrum.... so it will be permissible.
:OK, I now have the schematic in hand and looks like your video section is processed thru two triode sections of a 12AU7 schematically assigned as V8 . Initially take a voltage reading of pin 1 at ~110 Vdc, pin3 at ~1 Vdc, pin 6 at ~330 Vdc and pin 8 at ~18Vdc. If those are in the ballpark move on to look at the schema where you will see the 1N64 det diode...as prophesized... series feeding thru L10 then L11 coils and on into the 1st grid of V8a pin 2. At this same point a reference is also fed down to the V9 AGC triode. At this time get your best picture possible on the set and then move down and find R134....your sets AGC control. Take a fine point blue Sharpie and make a reference "tick" mark on both the shaft and its adjunct collar so that the control could precisely be reset to its initial position if required. Now, adjusting the control should result in producing a progressively weaker and washed out gray picture in one direction, while the other direction should produce a more contrasty video and then the pic will overload and start producing a tearing, out of sync picture. Typically the control is properly adjusted by being just back from that instability threshold back to where a stable contrasty picture is acquired on the strongest station to be received. That adjustment could possibly even be your sole contrast/ weak video problem, had it been misadjusted by a prior, unknowledgeable person in turning all the set controls helter-skelter.
:That possibility covered, we are now considering the plate signal of V8a where the sound info is extracted via tranfo L15, and you are saying that the sound is strong and clear. Considering that we will assume that stage as being OK. Video is then fed into the 1st grid stage of V8b. Note the cathode...pin 8...is bypassed with C2 "D" section of a canned electrolytic, if that cap is bad you will be getting no contrast..Low Freq gain thru that stage...and a washed out picture and minimal contrast control action. I like to see that unit be replaced with a modern axial / radial leaded 47 ufd 25 WVDC single unit, right across its R 50 (680 ohm) shunting resistor. The next place of interest would be the companion plate circuitry of V8b at pin 6 where series wired peaking coil L13 and plate load inductor L14 reside. Coils in the video amp circuitry are abject to failures, particularly in the fine ga wire that is wound upon forms (sometimes , a resistors body)
:On this particular chassis check L10, L12, and L13 and see if they fall in that category. Then, system powered down and afterburners off, check those coils resistances, they should be low coil range ohmmages vice the shunt resistor value. E.G. take L13 if it was reading 22k you would know that coil is open and that would also produce a very weak gray picture performance ..case closed. However, you really should have caught the side effect of decreased passage of supply voltage to pin 6 when measuring it back at initial voltage tests. But, as you can see, the same variants being possible at the other shunted inductors mentioned. That encompasses your complete video sequence from det to the injection to kine... pin 2.... 1st grid circuit. The cathode...pin 11... is where the sets brightness parameters are established. If brightness control range is normal, the only thing of any importance with that area being the C53 .022 ufd (no DC level leakage tolerated) cap feeding in a vert pulse from the vertical circuit for blanking out and the creation of vertical retrace blanking for the created video display.
:If none of these sequences were your problem, then the injection of Audio in for a video signal is in order, as was earlier mentioned.
:
:BTW...attached herewith is a relative reference thumbnail Zenith schema for any popcorn spectators in the peanut gallery.
:
:Location: http://img476.imageshack.us/img476/8455/zenagcvideo22ns.jpg
:
:73's de Edd
:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:Hi Edd
Oky doky, I will proceed with the outlined voltage checks and coils etc... will let you know what I come up with, and thanks for the info at the below address will get it a print it off, thanks so much for the excellent detailed information.
Mark

::::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::::::I only see two threads relevant to the det diode topic, with no further reference relating to the
::::::particular brand and chassis that you are working with. However, with that specific kinescope
::::::number utilized, it would have to go back to day one of B& W televison receivers.
::::::As for your fear of possible reverse installation of the detector diode, don't even think about it,
::::::as any damaging effect would be negated by virtue of the miniscule 100's of millivolt levels
::::::being involved. This not a situation like a power rectifier diode being reversed in its installation
::::::......a la..... ka-BOOM on power up..
::::::However, in such a situation, the one thing that would be INSTANTLY recognizable in case of a
::::::reversed diode installation would be the reverse produced video, wherein the picture would
::::::resemble a photographic negative. Along with an improper creation of sync with an adjunct
::::::tearing, bending and fluttering of the resultant picture being created.
::::::Sould your test equipment access include an audio generator it would be possible to start
::::::at the kine cathode/or/1st grid (I don't know your model...to schema reference...so, almost
::::::universally the 1st grid where video drive is injected). There you would inject, thru a .1 ufd/
::::::400VDC paper/poly isolation capacitor, a ~400 cycle 15 VP/P sine which should swamp
::::::the kine and produce a nice gradiated black series of hoz lines for its video display.
::::::(Should the generator have square wave capability, switching to that signal output mode
::::::would produce a very distinct black white transition between the lines). I still prefer the sine,
::::::as some degree of stage gain can be discerned in the transitional shading of the pattern
::::::from grey to black. From that point it is just a matter of working back thru the video output
::::::plate stage and its coupling component elements and then on to the first grid stage of that
::::::tube ( progressively decreasing signal input level as required) until a inpointing of a loss or
::::::severe weakening of stage gain shows up.
::::::Some sets even used a tandem of two tubes in their video output circuitry, but eventually you
::::::should end up at the video's derivation point, the video detector diode ( The majority of sets
::::::utilizing the then popular 1N60 series of "geranium" diodes). Two other common things to
::::::watch for would be a contrast control problem or an aged / dried out / low capacitance cathode
::::::bypass electrolytic capacitor.
::::::This signal injecton technique should present you with a sledge hammer to tack hammer signal
::::::variance in troubleshooting of even the worse of video conditions.
::::::Sir Norms extraction of raw composite video from a VCR'uh's back RCA jack ( Still utilizing
::::::the isolation capacitor for injection) should suffice if you had a modicum of video gain through
::::::lower level stages.
::::::However, nowadays, my preference is the utilization of a Video DVD player, they almost
::::::universally generate an internal ROM accessed test pattern (manufacturers propoganda
::::::oriented) the instant the unit is powered up from out of standby. No DVD being required, until
::::::the point whereyou really want / need to evaluate with some changing video.
::::::
::::::73's de Edd
::::::
::::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::::::
:::::::Hi All
::::::: Well I determined which way the diode went in, but ufortunately I still have the same result, weak picture, the sound seems to be ok, but thats about it, honestly at this point I'm just about to throw in the towel on this one, just don't know where too go from here, any ideas would be very much appreciated:)
:::::::Mark
:::::::Hi Edd
::::: Thank you so much for the very detailed info, this is what I've been hoping someone would reply with, you have given me a very good idea as too what might be going on, I'm printing off this page for refernence, the model I'm working with is a Zenith G2322, not sure of the chassis # off hand, but if you would like I can send you a copy of the SAMS schematic I have for it, let me know, in the mean time I'm taking you advice to heart, thank you so much! sounds like you really know these old TV's:)
:::::Mark
::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::::Rgr….Rgr…. Take the info that I have supplied and proceed, considering that you have access to an AF audio sig generator…in the interim I will dig deeeeeeep into the “Dust Bin” ....may take awhile...and extract Sir Samuels Folder 98 # 17 and research the circuitry to further refine the troubleshooting technique specific to that chassis....
::::73’s de Edd
::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Hi Edd
::: Will do, I have also replaced the contrast control, just on an outside chance, also I must tell you I have in the past tence already gone through and replaced all capacitors and resistors that were bad or way out of tolerance, let me know if you find this SAMS and any other info relating to this problem will be greatly appreciated:)
:::Mark
:::Hi Edd
:: I have discovered a problem in doing what you state, there is a harness that connects between the TV Chassis and the Radio, when disconnected and the TV chassis is out of the cabinet, I cannot power up the TV chassis by itself, I'm not sure, but would assume way back when, they must have had a dummy plug they connected too this harness in order to work on the TV chassis by itself, stand alone, out of the cabinet, maybe you can enlighten me as too how too go about this so I can make the test you state in the previous, let me know, thanks:)
::Mark
:
:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:
:Initially, in responding to your octal chassis-interconnecting plug. I always liked to take readings from the top...especially with that cumbersome pic tube weight also being considered. You might possibly have some of the mini 7-9 pin adapter sockets to plug a tube into and then be able to have topside access to the test tabs that are arranged around that unit's top periphery. If not then take a short length of #26 insulated solid wire (Freebie....100 pair telephone trunk line wire..or also... common Telco attic wiring) and bare 1/4 in on each end. One end is twirled 3 times around the tube pin(s) concerned...easy with surgical tweezers.......then press them in against the glass end. The wire is then dressed up vertically to the tube side so that the other bared end is accessible for metering / sig injection / sig access. This technique doesn't fly at the RF strata...but we're only into audio and the video spectrum.... so it will be permissible.
:OK, I now have the schematic in hand and looks like your video section is processed thru two triode sections of a 12AU7 schematically assigned as V8 . Initially take a voltage reading of pin 1 at ~110 Vdc, pin3 at ~1 Vdc, pin 6 at ~330 Vdc and pin 8 at ~18Vdc. If those are in the ballpark move on to look at the schema where you will see the 1N64 det diode...as prophesized... series feeding thru L10 then L11 coils and on into the 1st grid of V8a pin 2. At this same point a reference is also fed down to the V9 AGC triode. At this time get your best picture possible on the set and then move down and find R134....your sets AGC control. Take a fine point blue Sharpie and make a reference "tick" mark on both the shaft and its adjunct collar so that the control could precisely be reset to its initial position if required. Now, adjusting the control should result in producing a progressively weaker and washed out gray picture in one direction, while the other direction should produce a more contrasty video and then the pic will overload and start producing a tearing, out of sync picture. Typically the control is properly adjusted by being just back from that instability threshold back to where a stable contrasty picture is acquired on the strongest station to be received. That adjustment could possibly even be your sole contrast/ weak video problem, had it been misadjusted by a prior, unknowledgeable person in turning all the set controls helter-skelter.
:That possibility covered, we are now considering the plate signal of V8a where the sound info is extracted via tranfo L15, and you are saying that the sound is strong and clear. Considering that we will assume that stage as being OK. Video is then fed into the 1st grid stage of V8b. Note the cathode...pin 8...is bypassed with C2 "D" section of a canned electrolytic, if that cap is bad you will be getting no contrast..Low Freq gain thru that stage...and a washed out picture and minimal contrast control action. I like to see that unit be replaced with a modern axial / radial leaded 47 ufd 25 WVDC single unit, right across its R 50 (680 ohm) shunting resistor. The next place of interest would be the companion plate circuitry of V8b at pin 6 where series wired peaking coil L13 and plate load inductor L14 reside. Coils in the video amp circuitry are abject to failures, particularly in the fine ga wire that is wound upon forms (sometimes , a resistors body)
:On this particular chassis check L10, L12, and L13 and see if they fall in that category. Then, system powered down and afterburners off, check those coils resistances, they should be low coil range ohmmages vice the shunt resistor value. E.G. take L13 if it was reading 22k you would know that coil is open and that would also produce a very weak gray picture performance ..case closed. However, you really should have caught the side effect of decreased passage of supply voltage to pin 6 when measuring it back at initial voltage tests. But, as you can see, the same variants being possible at the other shunted inductors mentioned. That encompasses your complete video sequence from det to the injection to kine... pin 2.... 1st grid circuit. The cathode...pin 11... is where the sets brightness parameters are established. If brightness control range is normal, the only thing of any importance with that area being the C53 .022 ufd (no DC level leakage tolerated) cap feeding in a vert pulse from the vertical circuit for blanking out and the creation of vertical retrace blanking for the created video display.
:If none of these sequences were your problem, then the injection of Audio in for a video signal is in order, as was earlier mentioned.
:
:BTW...attached herewith is a relative reference thumbnail Zenith schema for any popcorn spectators in the peanut gallery.
:
:Location: http://img476.imageshack.us/img476/8455/zenagcvideo22ns.jpg
:
:73's de Edd
:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:Hi Edd
In reference too R134? the only AGC Control I see on my SAMS is AGC DELAY R13, is this the control you are refering too? there is no R134 according too my SAMS.