Zenith SF2023H TV - no sound

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

Reply to
William R. Walsh
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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.

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Reply to
Anonymous

  1. > (The service number is SF2023H2.) The previous owner must have taken perf=

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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????

Reply to
hrhofmann

Hi!

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

Reply to
William R. Walsh

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