Please help.
Thanks,
Dave...
I hope this helps, if other questions let me know.
Poston
:Hello All,
: I replaced all paper and filter capacitors. All tubes test good. However I don't have any idea what the correct values for the resistors should be on the 12AT7. There were two open resistors and the 2 micro-henry coil seems to be open too. It is probably not oscillating. Absolutely zero reception. Beautiful raster though. Its in SAMs 121-10. I have a lot of folders from set 121 but not 10 unfortunately.
:
:Please help.
:
:Thanks,
:
:Dave...
Thanks,
Dave...
:Hi Dave,
:I have the SAMS 121-10. On the oscillator side of the 12AT7, at pin 6 (Plate) there is an 1800 ohm resistor to B+. Between pins 7 and 8 (grid-cathode) there is a 10K resistor. On the mixer side of the 12AT7 there is a 1200 ohm resistor from pin 3 (cathode) to ground. That cathode choke coil from pin 8 is specified at 2.2 microhenries, with 1.8 ohms DC resistance. All these resistors are 1/2 watt.
:Here are the voltages shown for the 12AT7:
:Pin 1: 120VDC
:Pin 2: 0V
:Pin 3: 2VDC
:Pin 4: 6.3VAC
:Pin 5: 6.3VAC
:Pin 6: 220VDC
:Pin 7: -5.2VDC (measured with VTVM)
:Pin 8: 0V
:Pin 9: 0V
:
:I hope this helps, if other questions let me know.
:Poston
:
:
::Hello All,
:: I replaced all paper and filter capacitors. All tubes test good. However I don't have any idea what the correct values for the resistors should be on the 12AT7. There were two open resistors and the 2 micro-henry coil seems to be open too. It is probably not oscillating. Absolutely zero reception. Beautiful raster though. Its in SAMs 121-10. I have a lot of folders from set 121 but not 10 unfortunately.
::
::Please help.
::
::Thanks,
::
::Dave...
Pin 1: 7.3K ohms (measured from +320VDC point)
Pin 2: 5.6K ohms
Pin 3: 1.2K ohms
Pin 4: .3 ohm
Pin 5: .3 ohm
Pin 6: 2K ohms (measured from +320VDC point)
Pin 7: 10K
Pin 8: 1.8 ohms
Pin 9: 0 ohms
Regarding connections, pin 1 (plate) and pin 2 (grid) would be the mixer portion of the 12AT7. Pin 1 connects directly to the 1st Video IF. Connected to pin 2 (grid) would be the following:
1) A 3.3 microhenry grid choke coil and thence through a 5600 ohm resistor to common negative.
2) An 8 MMF cap and thence to pin 5 (plate) of the 6CB6 RF amp.
3) A 2 MMF cap, and thence to pin 7 (grid) of the osc. section of the 12AT7.
I can't see how any resistor (let alone one which you describe) should be connected to pin 2 of the 12AT7. The resistor connected to pin 7 should be 10K ohms, which also connects to pin 8, as I mentioned in my earlier post.
Dave, I am trying my best to help but it is very difficult to describe a SAMS Photofact and schematic in words in a forum like this. You really need to have a copy of this Photofact, it is hard to believe you have proceeded thus far through this Motorola without one (I know I could not have done so). If you cannot find one through some other source, send me an email and I will see if I can xerox the necessary information and mail it to you.
Poston
:Poston,
: Thanks for your response. These resistors are really messed up in this tv. From pin 7 to 8 I measure 69 ohms. From Pin 3 to the chassis is no resistor at all. But there is a .4 ohm resistor connecting pin 3 to somewhere else. Yes, I disconnected it and measured it and its .4 ohms. There are two bands on it yellow and violet, for 4 7. There is a space between the bands. I doubt that this resistor was supposed to have such a low value. Other people added resistors in parallel with resistors. It's a big mess. It's difficult to find the pins with all those resistors there.
: Also, what is connected to pins 1 and 2? From pin 2 I have a resistor with two orange bands on it, with a space in between "3 3". This resistor measures 1.8K. There is another resistor connected to pin 7. It measures 23K ohms and has three bands "white, white white" (999? Not possible). I think it faded a little.
: When I clean up this "mess" (this mass of messy resistors), I'm sure it will work fine. Do you think anyone wants to see this? I can take a picture of it.
:
:Thanks,
:
:Dave...
::Hi Dave,
::I have the SAMS 121-10. On the oscillator side of the 12AT7, at pin 6 (Plate) there is an 1800 ohm resistor to B+. Between pins 7 and 8 (grid-cathode) there is a 10K resistor. On the mixer side of the 12AT7 there is a 1200 ohm resistor from pin 3 (cathode) to ground. That cathode choke coil from pin 8 is specified at 2.2 microhenries, with 1.8 ohms DC resistance. All these resistors are 1/2 watt.
::Here are the voltages shown for the 12AT7:
::Pin 1: 120VDC
::Pin 2: 0V
::Pin 3: 2VDC
::Pin 4: 6.3VAC
::Pin 5: 6.3VAC
::Pin 6: 220VDC
::Pin 7: -5.2VDC (measured with VTVM)
::Pin 8: 0V
::Pin 9: 0V
::
::I hope this helps, if other questions let me know.
::Poston
::
::
:::Hello All,
::: I replaced all paper and filter capacitors. All tubes test good. However I don't have any idea what the correct values for the resistors should be on the 12AT7. There were two open resistors and the 2 micro-henry coil seems to be open too. It is probably not oscillating. Absolutely zero reception. Beautiful raster though. Its in SAMs 121-10. I have a lot of folders from set 121 but not 10 unfortunately.
:::
:::Please help.
:::
:::Thanks,
:::
:::Dave...
Thanks,
Dave...
:Dave
:If it will help, here are the resistance measurements (per SAMS Photofact) from the 12AT7 socket. All measured resistances are from the socket pin to common negative unless otherwise noted:
:
:Pin 1: 7.3K ohms (measured from +320VDC point)
:Pin 2: 5.6K ohms
:Pin 3: 1.2K ohms
:Pin 4: .3 ohm
:Pin 5: .3 ohm
:Pin 6: 2K ohms (measured from +320VDC point)
:Pin 7: 10K
:Pin 8: 1.8 ohms
:Pin 9: 0 ohms
:
:Regarding connections, pin 1 (plate) and pin 2 (grid) would be the mixer portion of the 12AT7. Pin 1 connects directly to the 1st Video IF. Connected to pin 2 (grid) would be the following:
:
:1) A 3.3 microhenry grid choke coil and thence through a 5600 ohm resistor to common negative.
:2) An 8 MMF cap and thence to pin 5 (plate) of the 6CB6 RF amp.
:3) A 2 MMF cap, and thence to pin 7 (grid) of the osc. section of the 12AT7.
:
:I can't see how any resistor (let alone one which you describe) should be connected to pin 2 of the 12AT7. The resistor connected to pin 7 should be 10K ohms, which also connects to pin 8, as I mentioned in my earlier post.
:
:Dave, I am trying my best to help but it is very difficult to describe a SAMS Photofact and schematic in words in a forum like this. You really need to have a copy of this Photofact, it is hard to believe you have proceeded thus far through this Motorola without one (I know I could not have done so). If you cannot find one through some other source, send me an email and I will see if I can xerox the necessary information and mail it to you.
:Poston
:
:
::Poston,
:: Thanks for your response. These resistors are really messed up in this tv. From pin 7 to 8 I measure 69 ohms. From Pin 3 to the chassis is no resistor at all. But there is a .4 ohm resistor connecting pin 3 to somewhere else. Yes, I disconnected it and measured it and its .4 ohms. There are two bands on it yellow and violet, for 4 7. There is a space between the bands. I doubt that this resistor was supposed to have such a low value. Other people added resistors in parallel with resistors. It's a big mess. It's difficult to find the pins with all those resistors there.
:: Also, what is connected to pins 1 and 2? From pin 2 I have a resistor with two orange bands on it, with a space in between "3 3". This resistor measures 1.8K. There is another resistor connected to pin 7. It measures 23K ohms and has three bands "white, white white" (999? Not possible). I think it faded a little.
:: When I clean up this "mess" (this mass of messy resistors), I'm sure it will work fine. Do you think anyone wants to see this? I can take a picture of it.
::
::Thanks,
::
::Dave...
:::Hi Dave,
:::I have the SAMS 121-10. On the oscillator side of the 12AT7, at pin 6 (Plate) there is an 1800 ohm resistor to B+. Between pins 7 and 8 (grid-cathode) there is a 10K resistor. On the mixer side of the 12AT7 there is a 1200 ohm resistor from pin 3 (cathode) to ground. That cathode choke coil from pin 8 is specified at 2.2 microhenries, with 1.8 ohms DC resistance. All these resistors are 1/2 watt.
:::Here are the voltages shown for the 12AT7:
:::Pin 1: 120VDC
:::Pin 2: 0V
:::Pin 3: 2VDC
:::Pin 4: 6.3VAC
:::Pin 5: 6.3VAC
:::Pin 6: 220VDC
:::Pin 7: -5.2VDC (measured with VTVM)
:::Pin 8: 0V
:::Pin 9: 0V
:::
:::I hope this helps, if other questions let me know.
:::Poston
:::
:::
::::Hello All,
:::: I replaced all paper and filter capacitors. All tubes test good. However I don't have any idea what the correct values for the resistors should be on the 12AT7. There were two open resistors and the 2 micro-henry coil seems to be open too. It is probably not oscillating. Absolutely zero reception. Beautiful raster though. Its in SAMs 121-10. I have a lot of folders from set 121 but not 10 unfortunately.
::::
::::Please help.
::::
::::Thanks,
::::
::::Dave...
What was wrong to cause no sound/no picture?. Pin 6 had a resistor going to B+, it was open. The tube can't work if its not powered up. A choke was open due to someone putting a resistor across a capacitor that looks just like a resistor. It's small like a resistor but it's a 2 pf capacitor. This capacitor is connected from pin 6 to pin 8. So, with that resistor there, it caused a problem. The resistor was removed. The other things that resemble resistors are coils. One is .47 ohms, from pin 4 connecting to the filament circuit. This is only on the original service data, not in the SAMs photofact. The other choke has a 3.3 ohm resistance according to the service data. I measure 15. But everything works. Also, pin 1 was connected to pin 2. I don't think it could work well like that at all. It works quite well now.
Now to solve my horizontal problem. It's off frequency but after a few seconds, the picture shuts off. I have a funny feeling that the HV fuse adapter is loose and keeps disconnecting. It has to be something that simple.
Dave...
:Poston,
: I just receved the service data for this tv. I have both the original service data and the SAMs Photofact. The Motorola service data shows the .47 ohm resistor (actually a coil that looks like a resistor). Two other resistors are actually capacitors, each are 2pf. The both look like resistors. So this is a case of the old capacitor inside the resistor case trick. It was common back then to use this case. I had thought that that's what it was but until I received the schematic, I couldn't tell. I just removed a previous "repair" that someone did. They put a low value resistor across one of the 2pf capacitors.
::Poston,
:: I have ordered a copy of the entire set 121. I did before your first reply because I could see that someone had been in this tv before me and really made a mess of things.
:: There is a resistor running from pin 3 of the 12AT7 to the a terminal strip. If the tuner is in the lower right, then this connection is the left most on the terminal strip. The resistor measures .4 ohms. I believe that this resistor, in changing values, is the culprit. Or something drew excessive amounts of current through in, resulting in the open inductor.
:: I wish we had somewhere we could post pictures of what discussions are about. What if I create a Yahoo group for that purpose, for members only. Which means that before people can become members, I would have to check to see if they're actually posting messages here in this forum. I think it could work only if the owners of this forum approve.
:: I would like to show the picture of this mess in this tv. It's quite interesting. Thanks for your resistance values. Maybe I can solve this before I receive the SAMs set.
::
::Thanks,
::
::Dave...
:::Dave
:::If it will help, here are the resistance measurements (per SAMS Photofact) from the 12AT7 socket. All measured resistances are from the socket pin to common negative unless otherwise noted:
:::
:::Pin 1: 7.3K ohms (measured from +320VDC point)
:::Pin 2: 5.6K ohms
:::Pin 3: 1.2K ohms
:::Pin 4: .3 ohm
:::Pin 5: .3 ohm
:::Pin 6: 2K ohms (measured from +320VDC point)
:::Pin 7: 10K
:::Pin 8: 1.8 ohms
:::Pin 9: 0 ohms
:::
:::Regarding connections, pin 1 (plate) and pin 2 (grid) would be the mixer portion of the 12AT7. Pin 1 connects directly to the 1st Video IF. Connected to pin 2 (grid) would be the following:
:::
:::1) A 3.3 microhenry grid choke coil and thence through a 5600 ohm resistor to common negative.
:::2) An 8 MMF cap and thence to pin 5 (plate) of the 6CB6 RF amp.
:::3) A 2 MMF cap, and thence to pin 7 (grid) of the osc. section of the 12AT7.
:::
:::I can't see how any resistor (let alone one which you describe) should be connected to pin 2 of the 12AT7. The resistor connected to pin 7 should be 10K ohms, which also connects to pin 8, as I mentioned in my earlier post.
:::
:::Dave, I am trying my best to help but it is very difficult to describe a SAMS Photofact and schematic in words in a forum like this. You really need to have a copy of this Photofact, it is hard to believe you have proceeded thus far through this Motorola without one (I know I could not have done so). If you cannot find one through some other source, send me an email and I will see if I can xerox the necessary information and mail it to you.
:::Poston
:::
:::
::::Poston,
:::: Thanks for your response. These resistors are really messed up in this tv. From pin 7 to 8 I measure 69 ohms. From Pin 3 to the chassis is no resistor at all. But there is a .4 ohm resistor connecting pin 3 to somewhere else. Yes, I disconnected it and measured it and its .4 ohms. There are two bands on it yellow and violet, for 4 7. There is a space between the bands. I doubt that this resistor was supposed to have such a low value. Other people added resistors in parallel with resistors. It's a big mess. It's difficult to find the pins with all those resistors there.
:::: Also, what is connected to pins 1 and 2? From pin 2 I have a resistor with two orange bands on it, with a space in between "3 3". This resistor measures 1.8K. There is another resistor connected to pin 7. It measures 23K ohms and has three bands "white, white white" (999? Not possible). I think it faded a little.
:::: When I clean up this "mess" (this mass of messy resistors), I'm sure it will work fine. Do you think anyone wants to see this? I can take a picture of it.
::::
::::Thanks,
::::
::::Dave...
:::::Hi Dave,
:::::I have the SAMS 121-10. On the oscillator side of the 12AT7, at pin 6 (Plate) there is an 1800 ohm resistor to B+. Between pins 7 and 8 (grid-cathode) there is a 10K resistor. On the mixer side of the 12AT7 there is a 1200 ohm resistor from pin 3 (cathode) to ground. That cathode choke coil from pin 8 is specified at 2.2 microhenries, with 1.8 ohms DC resistance. All these resistors are 1/2 watt.
:::::Here are the voltages shown for the 12AT7:
:::::Pin 1: 120VDC
:::::Pin 2: 0V
:::::Pin 3: 2VDC
:::::Pin 4: 6.3VAC
:::::Pin 5: 6.3VAC
:::::Pin 6: 220VDC
:::::Pin 7: -5.2VDC (measured with VTVM)
:::::Pin 8: 0V
:::::Pin 9: 0V
:::::
:::::I hope this helps, if other questions let me know.
:::::Poston
:::::
:::::
::::::Hello All,
:::::: I replaced all paper and filter capacitors. All tubes test good. However I don't have any idea what the correct values for the resistors should be on the 12AT7. There were two open resistors and the 2 micro-henry coil seems to be open too. It is probably not oscillating. Absolutely zero reception. Beautiful raster though. Its in SAMs 121-10. I have a lot of folders from set 121 but not 10 unfortunately.
::::::
::::::Please help.
::::::
::::::Thanks,
::::::
::::::Dave...