What voltage do you have on pin 27 of U3101 (speakers off)? It should be .02 on and 2.29 off. Also, check the external speaker switch to see if it has gotten "dusty" over time. It seems there was also a muting transistor that was a culprit on this chassis, but I can't remember which one.
Good luck,
Joe
walter wood wrote:
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:[EMAIL PROTECTED]
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