Sound trouble on GE 27GT720 (Chassis CTC203AX1) -- Need help...
 

Greetings sci.electronics.repair community,

I have a GE TV that has a really weird audio problem. The TV information
is as follows:

Model #: 27GT720
Service #: 27GT720TX2
Chassis #: CTC203AX1

While watching the set, the audio will randomly disappear (from all
channels, this particular set is a low-end model with no baseband inputs, so
the only audio I can verify this with is from the internal tuner). When the
tuner sound goes away, you are left with a barely audible hiss which does
vary in intensity with the volume control, so I believe the final stage of
the output amplifier is fine.

The weird part is that once the sound goes away, it will stay away for as
long as the set is powered off, as long as it is plugged into the wall. If
I unplug the power and plug it back in, the sound will return and function
normally for a random amount of time (typically not less than 20min and not
more than 1hr). I first suspected thermal problems when observing this, but
if I unplug the set immediately after the audio goes away, it will still
return right away and may stay on for over an hour before failing again. If
the sound would disappear entirely and never come back, or at least not
return until the set cooled down, this problem would make more sense to me.

I have not fixed a television set in particular before, but I am used to
the safety issues and precautions for working around high voltage supplies
and have experience working around CRTs in devices other than televisions.
I do have respectible soldering skills and access to hot air tools for
surface mount rework if required to make a repair.

Can anyone give me a pointer as to what may be going wrong here?

Thank you!

Scott

Sound trouble on GE 27GT720 (Chassis CTC203AX1) -- Need help...
 

Scott_SS wrote:
Greetings sci.electronics.repair community,

I have a GE TV that has a really weird audio problem. The TV information
is as follows:

Model #: 27GT720
Service #: 27GT720TX2
Chassis #: CTC203AX1

While watching the set, the audio will randomly disappear (from all
channels, this particular set is a low-end model with no baseband inputs, so
the only audio I can verify this with is from the internal tuner). When the
tuner sound goes away, you are left with a barely audible hiss which does
vary in intensity with the volume control, so I believe the final stage of
the output amplifier is fine.

The weird part is that once the sound goes away, it will stay away for as
long as the set is powered off, as long as it is plugged into the wall. If
I unplug the power and plug it back in, the sound will return and function
normally for a random amount of time (typically not less than 20min and not
more than 1hr).

Can anyone give me a pointer as to what may be going wrong here?

Thank you!

Scott

Common problem with that model and the Gemstar4 module. The unit
misinterprets a Data signal which turns off the audio. There was even
a lawsuit for the problem. I have not seen one do this often and
within 20 minutes, so If you can confirm that the tv does not do it
with a proper signal generator with audio, then it is more than likely
related to the Gemstar module.

At that point you will have to confirm that the tv station you are
putting on the tv is clean, no ghosting/snow as poor antenna signal can
cause this also, and not sending out the bad data to the Gemstar
module. Then verify good sync data lines are getting to the Gemstar
module. Then troubleshoot the Gemstar mute line coming out of the
module to the audio system.

You may need a digital storage o'scope to speed along your
troubleshooting for this type of repair.

David

Sound trouble on GE 27GT720 (Chassis CTC203AX1) -- Need help...
 

I just ran into one of these recently too. check out this article.
You'll find it interesting. Lenny Stein, Barlen Electronics.

http://www.iwaynet.net/~nesda/SilentCTC.html