Hello All,
I have been working on this tv on and off for about a year now. I have tried many things but the sound stays strong and there is virtually zero contrast. The picture can just barely be seen. When I turn the contrast control down, the audio is affected too. There is less audio when the contrast control is turned down. I have taken out the tuner and examined everything thoroughly. I believe it is working fine.
I have removed and examined the solder side of the pc board and found a few little things but nothing major. All paper and filter capacitors were replaced. I am wondering if this could be the video detector diode. That doesn't seem to make any sense.
If I have sound, then why is the contrast so weak? It just doesn't make any sense. If I have sound, doesn't that mean that the video is fine? DC restoration is great I the brightness control works fine. There is a picture but it's so weak that it's unwatchable.
Please help. I am about to give up on this set.

Thanks,

Dave...

Hi Dave

What happens when brightness is turned up? If the picture tube is good contrast is determined by Vidio amplifiers & video IF stages. Yes, video detector could be the problem. In older TV's it was a 6AL5, later ones germanium diode.

Sound is taken off after vidio IF stages in later TV's. Vidio IF's could still be weak and some sound would come through.

Norm

:Hello All,
: I have been working on this tv on and off for about a year now. I have tried many things but the sound stays strong and there is virtually zero contrast. The picture can just barely be seen. When I turn the contrast control down, the audio is affected too. There is less audio when the contrast control is turned down. I have taken out the tuner and examined everything thoroughly. I believe it is working fine.
: I have removed and examined the solder side of the pc board and found a few little things but nothing major. All paper and filter capacitors were replaced. I am wondering if this could be the video detector diode. That doesn't seem to make any sense.
: If I have sound, then why is the contrast so weak? It just doesn't make any sense. If I have sound, doesn't that mean that the video is fine? DC restoration is great I the brightness control works fine. There is a picture but it's so weak that it's unwatchable.
: Please help. I am about to give up on this set.
:
:Thanks,
:
:Dave...

Norm,
When I turn up the brightness, the raster gets bright but the picture can no longer be seen. This is a Hot Chassis set with very few stages. It is an 8AW8 sync sepapator/video amp tube. The contrast and brightness are connected after the output of the video amp. The signal goes through a an r-l-c network and then through a capacitor to the cathode of the picture tube. There's not much there. There are no video stages past that, just the audio IF and amp.
There is a diode diode detector. I'll use one of my 1N34As.
So the video detector can be defective, yet sound can get through? Interesting. The sound is quite good. I will try replacing the diode and get back to you later. I want to be through with this set before the week-end is over.

Thanks very much,

Dave...

:Hi Dave
:
: What happens when brightness is turned up? If the picture tube is good contrast is determined by Vidio amplifiers & video IF stages. Yes, video detector could be the problem. In older TV's it was a 6AL5, later ones germanium diode.
:
: Sound is taken off after vidio IF stages in later TV's. Vidio IF's could still be weak and some sound would come through.
:
:Norm
:
::Hello All,
:: I have been working on this tv on and off for about a year now. I have tried many things but the sound stays strong and there is virtually zero contrast. The picture can just barely be seen. When I turn the contrast control down, the audio is affected too. There is less audio when the contrast control is turned down. I have taken out the tuner and examined everything thoroughly. I believe it is working fine.
:: I have removed and examined the solder side of the pc board and found a few little things but nothing major. All paper and filter capacitors were replaced. I am wondering if this could be the video detector diode. That doesn't seem to make any sense.
:: If I have sound, then why is the contrast so weak? It just doesn't make any sense. If I have sound, doesn't that mean that the video is fine? DC restoration is great I the brightness control works fine. There is a picture but it's so weak that it's unwatchable.
:: Please help. I am about to give up on this set.
::
::Thanks,
::
::Dave...

Hi Dave

That's good news. Since the screen does get bright your picture tube should be ok. I would work on replacing that diode and the checking 8AW8 circuit.

A 1N34 diode will work but the original was probably a diode rated as a video detector?

Norm

:Norm,
: When I turn up the brightness, the raster gets bright but the picture can no longer be seen. This is a Hot Chassis set with very few stages. It is an 8AW8 sync sepapator/video amp tube. The contrast and brightness are connected after the output of the video amp. The signal goes through a an r-l-c network and then through a capacitor to the cathode of the picture tube. There's not much there. There are no video stages past that, just the audio IF and amp.
: There is a diode diode detector. I'll use one of my 1N34As.
:So the video detector can be defective, yet sound can get through? Interesting. The sound is quite good. I will try replacing the diode and get back to you later. I want to be through with this set before the week-end is over.
:
:Thanks very much,
:
:Dave...
:
::Hi Dave
::
:: What happens when brightness is turned up? If the picture tube is good contrast is determined by Vidio amplifiers & video IF stages. Yes, video detector could be the problem. In older TV's it was a 6AL5, later ones germanium diode.
::
:: Sound is taken off after vidio IF stages in later TV's. Vidio IF's could still be weak and some sound would come through.
::
::Norm
::
:::Hello All,
::: I have been working on this tv on and off for about a year now. I have tried many things but the sound stays strong and there is virtually zero contrast. The picture can just barely be seen. When I turn the contrast control down, the audio is affected too. There is less audio when the contrast control is turned down. I have taken out the tuner and examined everything thoroughly. I believe it is working fine.
::: I have removed and examined the solder side of the pc board and found a few little things but nothing major. All paper and filter capacitors were replaced. I am wondering if this could be the video detector diode. That doesn't seem to make any sense.
::: If I have sound, then why is the contrast so weak? It just doesn't make any sense. If I have sound, doesn't that mean that the video is fine? DC restoration is great I the brightness control works fine. There is a picture but it's so weak that it's unwatchable.
::: Please help. I am about to give up on this set.
:::
:::Thanks,
:::
:::Dave...

Norm,
All I have are 1N34As on hand and I want to get done this weekend. If it works, that should be fine. There's so little in that 8AW8 video output circuit, I could replace it all, except for the coils. I don't see anything wrong with anything, however I have seen strange things before in other radios and TVs.

Thanks again,

Dave...
:Hi Dave
:
: That's good news. Since the screen does get bright your picture tube should be ok. I would work on replacing that diode and the checking 8AW8 circuit.
:
: A 1N34 diode will work but the original was probably a diode rated as a video detector?
:
:Norm
:
::Norm,
:: When I turn up the brightness, the raster gets bright but the picture can no longer be seen. This is a Hot Chassis set with very few stages. It is an 8AW8 sync sepapator/video amp tube. The contrast and brightness are connected after the output of the video amp. The signal goes through a an r-l-c network and then through a capacitor to the cathode of the picture tube. There's not much there. There are no video stages past that, just the audio IF and amp.
:: There is a diode diode detector. I'll use one of my 1N34As.
::So the video detector can be defective, yet sound can get through? Interesting. The sound is quite good. I will try replacing the diode and get back to you later. I want to be through with this set before the week-end is over.
::
::Thanks very much,
::
::Dave...
::
:::Hi Dave
:::
::: What happens when brightness is turned up? If the picture tube is good contrast is determined by Vidio amplifiers & video IF stages. Yes, video detector could be the problem. In older TV's it was a 6AL5, later ones germanium diode.
:::
::: Sound is taken off after vidio IF stages in later TV's. Vidio IF's could still be weak and some sound would come through.
:::
:::Norm
:::
::::Hello All,
:::: I have been working on this tv on and off for about a year now. I have tried many things but the sound stays strong and there is virtually zero contrast. The picture can just barely be seen. When I turn the contrast control down, the audio is affected too. There is less audio when the contrast control is turned down. I have taken out the tuner and examined everything thoroughly. I believe it is working fine.
:::: I have removed and examined the solder side of the pc board and found a few little things but nothing major. All paper and filter capacitors were replaced. I am wondering if this could be the video detector diode. That doesn't seem to make any sense.
:::: If I have sound, then why is the contrast so weak? It just doesn't make any sense. If I have sound, doesn't that mean that the video is fine? DC restoration is great I the brightness control works fine. There is a picture but it's so weak that it's unwatchable.
:::: Please help. I am about to give up on this set.
::::
::::Thanks,
::::
::::Dave...

Norm,
I found the problem in between the 3rd IF amp and video output tube. I now have a very strong picture.

Thank very much for your help,

Dave...
:Norm,
: All I have are 1N34As on hand and I want to get done this weekend. If it works, that should be fine. There's so little in that 8AW8 video output circuit, I could replace it all, except for the coils. I don't see anything wrong with anything, however I have seen strange things before in other radios and TVs.
:
:
:Thanks again,
:
:Dave...
::Hi Dave
::
:: That's good news. Since the screen does get bright your picture tube should be ok. I would work on replacing that diode and the checking 8AW8 circuit.
::
:: A 1N34 diode will work but the original was probably a diode rated as a video detector?
::
::Norm
::
:::Norm,
::: When I turn up the brightness, the raster gets bright but the picture can no longer be seen. This is a Hot Chassis set with very few stages. It is an 8AW8 sync sepapator/video amp tube. The contrast and brightness are connected after the output of the video amp. The signal goes through a an r-l-c network and then through a capacitor to the cathode of the picture tube. There's not much there. There are no video stages past that, just the audio IF and amp.
::: There is a diode diode detector. I'll use one of my 1N34As.
:::So the video detector can be defective, yet sound can get through? Interesting. The sound is quite good. I will try replacing the diode and get back to you later. I want to be through with this set before the week-end is over.
:::
:::Thanks very much,
:::
:::Dave...
:::
::::Hi Dave
::::
:::: What happens when brightness is turned up? If the picture tube is good contrast is determined by Vidio amplifiers & video IF stages. Yes, video detector could be the problem. In older TV's it was a 6AL5, later ones germanium diode.
::::
:::: Sound is taken off after vidio IF stages in later TV's. Vidio IF's could still be weak and some sound would come through.
::::
::::Norm
::::
:::::Hello All,
::::: I have been working on this tv on and off for about a year now. I have tried many things but the sound stays strong and there is virtually zero contrast. The picture can just barely be seen. When I turn the contrast control down, the audio is affected too. There is less audio when the contrast control is turned down. I have taken out the tuner and examined everything thoroughly. I believe it is working fine.
::::: I have removed and examined the solder side of the pc board and found a few little things but nothing major. All paper and filter capacitors were replaced. I am wondering if this could be the video detector diode. That doesn't seem to make any sense.
::::: If I have sound, then why is the contrast so weak? It just doesn't make any sense. If I have sound, doesn't that mean that the video is fine? DC restoration is great I the brightness control works fine. There is a picture but it's so weak that it's unwatchable.
::::: Please help. I am about to give up on this set.
:::::
:::::Thanks,
:::::
:::::Dave...

Norm,
More specifically it was between the output from the video detector and the video output tube. All is well. Now is the difficult part, re-assembling the TV.

Thanks,

Dave...
:Norm,
: I found the problem in between the 3rd IF amp and video output tube. I now have a very strong picture.
:
:Thank very much for your help,
:
:Dave...
::Norm,
:: All I have are 1N34As on hand and I want to get done this weekend. If it works, that should be fine. There's so little in that 8AW8 video output circuit, I could replace it all, except for the coils. I don't see anything wrong with anything, however I have seen strange things before in other radios and TVs.
::
::
::Thanks again,
::
::Dave...
:::Hi Dave
:::
::: That's good news. Since the screen does get bright your picture tube should be ok. I would work on replacing that diode and the checking 8AW8 circuit.
:::
::: A 1N34 diode will work but the original was probably a diode rated as a video detector?
:::
:::Norm
:::
::::Norm,
:::: When I turn up the brightness, the raster gets bright but the picture can no longer be seen. This is a Hot Chassis set with very few stages. It is an 8AW8 sync sepapator/video amp tube. The contrast and brightness are connected after the output of the video amp. The signal goes through a an r-l-c network and then through a capacitor to the cathode of the picture tube. There's not much there. There are no video stages past that, just the audio IF and amp.
:::: There is a diode diode detector. I'll use one of my 1N34As.
::::So the video detector can be defective, yet sound can get through? Interesting. The sound is quite good. I will try replacing the diode and get back to you later. I want to be through with this set before the week-end is over.
::::
::::Thanks very much,
::::
::::Dave...
::::
:::::Hi Dave
:::::
::::: What happens when brightness is turned up? If the picture tube is good contrast is determined by Vidio amplifiers & video IF stages. Yes, video detector could be the problem. In older TV's it was a 6AL5, later ones germanium diode.
:::::
::::: Sound is taken off after vidio IF stages in later TV's. Vidio IF's could still be weak and some sound would come through.
:::::
:::::Norm
:::::
::::::Hello All,
:::::: I have been working on this tv on and off for about a year now. I have tried many things but the sound stays strong and there is virtually zero contrast. The picture can just barely be seen. When I turn the contrast control down, the audio is affected too. There is less audio when the contrast control is turned down. I have taken out the tuner and examined everything thoroughly. I believe it is working fine.
:::::: I have removed and examined the solder side of the pc board and found a few little things but nothing major. All paper and filter capacitors were replaced. I am wondering if this could be the video detector diode. That doesn't seem to make any sense.
:::::: If I have sound, then why is the contrast so weak? It just doesn't make any sense. If I have sound, doesn't that mean that the video is fine? DC restoration is great I the brightness control works fine. There is a picture but it's so weak that it's unwatchable.
:::::: Please help. I am about to give up on this set.
::::::
::::::Thanks,
::::::
::::::Dave...

Congratulations. I just wanted to mention something about contrast controls. I don't have too much experience with televisions. I know how they work. I've adjusted many (picture size, convergence, etc.), but I've only worked extensively on a few, primarily my RCA 630TS. Regarding the contrast control, on many more modern sets (not necessarily your's), the contrast control only controls the gain of the video circuits. However, on my 630TS (and possibly your television), the contrast control controls the gain of the primary RF stages which do the work for both the audio and the video. This explains why the audio is affected when the contrast control is adjusted. In the case of my set, what should have been done is to put an AGC (automatic gain control) circuit in the primary RF stages and leave the contrast control for just the video stages. They didn't do this, though, so you must adjust the contrast for each channel on my set, and adjusting the contrast affects the audio. You may have a similar problem, though not necessarily as drastic. I would hope that some sort of AGC was manufactured into your set.

Thomas