[TechAssist] CTC169BG5 Audio problem additional info

Recap"
This set has a great picture, but the sound would
go off in about 5 seconds.
List members were generous in providing schematics.
One tech suggested opening up the DC sense line to
see if that was the problem.
I unsoldered pin 16 of JS1900.
The audio stays on longer now, but still shuts off.
There is a slight thump in the speakers at turn on,
but nothing unusual at all when the sound
disappears.
I got out my trusty Radio Shack audio signal tracer
and I have sound on pin 7 of U1901 and U1902 at all
times.
This can be varied with the sets volume control as
it should.
Pins 2 and 4 have the required +17 and -17.
Pin 3 shows -12.3 on the schematic.
there is -17 there at plug in.
That goes to -13 when sound is present, then goes
to app. -15 when the sound disappers.
The afore mentioned pin 16 JS1900 is still
unsoldered.
This might be a clue.
When I was testing the voltages the probe slopped
and I temporally shorted Pin 5 to 3 on U1901, and
the sound returned briefly.
I have to admit that I don't understand this
mute/DC sense circuit.
Anyone got any clues at this point?
TIA
Walter 

=====
Walter Wood                  
Future Tech Home Center        
2786 Hwy. 43 N.
Lawrenceburg Tn. 38464
931-829-3337
Fax 931-829-4044
mailto:wwood_38478@xxxxxxxxx

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