Zenith SF2023H TV - no sound

W

William R. Walsh

Guest
Hello all...

Another TV followed me home, this time a Zenith SF2023 model, made in 1989.
(The service number is SF2023H2.) The previous owner must have taken perfect
care of it--the thing is immaculate. And the picture quality is
excellent--focus is good, brightness and contrast also have more than enough
range. I even got the remote and it works.

But there's no sound coming out of this TV, and it "knows" this as it says
"muted" all the time. Pressing the MUTE button has no visible effect.
Pressing the volume buttons (either way) will cause the MUTED message to
disappear for a split second. I can hear some crackling in the speaker when
the TV comes on or turns off. If I put my ear up to it, I can hear a faint
hiss from the speaker, but nothing that sounds even faintly like a TV
program, even when tinkering with the volume controls.

The speaker is hooked up and tests good. The audio functionality in this TV
appears to be centered on a daughtercard mounted near the rear of the
mainboard. There's not much on this board--a capacitor, some "other stuff"
and a Philips integrated audio amplifier (of unknown type--haven't looked
yet) is it.

Any ideas? I've already checked for any speaker switches (found none), tried
the "master reset" command in the menu (seems to affect the picture only)
and gave the TV a good "shakedown" test to see if I could find cold solder
joints (it didn't change behavior in any way).

William
 
You've started with the speaker, so work backward from there.
Get the specs on the Audio and IF-Video Jungle chips. Inject a test signal into
the input of the audio chip. See if it has a mute pin and desolder and isolate,
ground or tie high... depending on the chip and what it "sees" as a unmuted
signal. With a Signal tracer, see if any audio from the IF-Video Jungle chip.
Check any and all transistors between the CPU mute out to the audio circuits as
well as any diodes in the circuit. Check for any bridges of recently killed bugs
or other material around the pins of the chips.



The speaker is hooked up and tests good. The audio functionality in this TV
appears to be centered on a daughtercard mounted near the rear of the
mainboard. There's not much on this board--a capacitor, some "other stuff"
and a Philips integrated audio amplifier (of unknown type--haven't looked
yet) is it.

Any ideas? I've already checked for any speaker switches (found none), tried
the "master reset" command in the menu (seems to affect the picture only)
and gave the TV a good "shakedown" test to see if I could find cold solder
joints (it didn't change behavior in any way).
Click to expand...

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On Sep 10, 6:02 pm, "William R. Walsh"
<newsgrou...@idontwantjunqueemail.walshcomptech.com> wrote:
Hello all...

Another TV followed me home, this time a Zenith SF2023 model, made in 1989.
(The service number is SF2023H2.) The previous owner must have taken perfect
care of it--the thing is immaculate. And the picture quality is
excellent--focus is good, brightness and contrast also have more than enough
range. I even got the remote and it works.

But there's no sound coming out of this TV, and it "knows" this as it says
"muted" all the time. Pressing the MUTE button has no visible effect.
Pressing the volume buttons (either way) will cause the MUTED message to
disappear for a split second. I can hear some crackling in the speaker when
the TV comes on or turns off. If I put my ear up to it, I can hear a faint
hiss from the speaker, but nothing that sounds even faintly like a TV
program, even when tinkering with the volume controls.

The speaker is hooked up and tests good. The audio functionality in this TV
appears to be centered on a daughtercard mounted near the rear of the
mainboard. There's not much on this board--a capacitor, some "other stuff"
and a Philips integrated audio amplifier (of unknown type--haven't looked
yet) is it.

Any ideas? I've already checked for any speaker switches (found none), tried
the "master reset" command in the menu (seems to affect the picture only)
and gave the TV a good "shakedown" test to see if I could find cold solder
joints (it didn't change behavior in any way).

William
Click to expand...
You need a scope to trace the lack of signal back from the output to
the output of the video jungle/sound card that is used in almost all
sets. Do you have a scope, do you have a schematic????
 
Hi!

You need a scope to trace the lack of signal back from the
output to the output of the video jungle/sound card that is
used in almost all sets. Do you have a scope, do you have
a schematic????
Click to expand...
I used to have a scope, but a basement flood "ate" it and I've never
looked into replacing it.

Nor do I have a schematic. However, the circuit itself seems pretty
straightforward, and with a little luck and some careful work, I think
I can get through it.

William
 
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