Sony FD-230 audio

[dtvmcdonald]

I have two Sony FD-230 Watchman TVs (about 2"). One works perfectly.
The other has perfect picture and no sound, except rarely a little
noise upon turn-on for a second or so.


The receiver part generates proper audio which makes it to the volume control.
The signal does not make it through the audio amp IC. I have the manual and the datasheet for the IC, which is still (barely ... last shipment Dec 31 2020) readily available.

The B+ voltage on the IC is one volt rather than 5 as the manual says.
There is an 18 ohm resistor in series with the B+ to the IC and an
electrolytic filtering the IC pin. Other pins have similarly low voltages.

What protocol should I follow in diagnosing and fixing this? The electrolytics
are tiny radials, the resistors and smaller caps are surface mount, tiny but easily accessible.

Edit: I realize that the correct protocol is "buy another working one real cheap", which I already did once,
but that's no challange for occupying <forbidden subject> boring days.

[zeno]

Odds are the IC is shorted. If so it & the 18 ohm should get hot to the feel.
Anything else on that pin is suspect next ( cap to GND )
Next is the output pin. Normally its apx 1/2 of the B+ voltage
to the IC then cap coupled to the head jack & SPKR.
On thru hole IC's its simple to lift pins to test BUT with SMD's a PIA
so if you have good eyes & steady hands change the chip.

73 Zeno
LFOD !