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Ok so I found a shorted jfet. Q1 in the mute section between the last opamp and the PA.
I removed all power transistors from PA2 to see if it had any effect. Doesn't seem to.
I now still have these conditions with the bulb limiter in place.
PA1
Negative 12-16 DCmv on output no load
Connecting load results in hum
All PA Vbe look GOOD. Very symmetrical around +/- 590mv.
213mvAC on output no load
Eliminated the bulb and used variac.
-1.5vDC on output as turn up all the way... turned it off quickly and things smell hot.
So I'm quite stuck...again. it's very challenging as the transistor voltages look good.
Oh and -27mv on Q1/2 jfet drains. (Between last opamp and PA).
And U100 (last opamp)
Pin7 -21mv
Pin6 -3mv
Pin5 -3.3mv
I removed all power transistors from PA2 to see if it had any effect. Doesn't seem to.
I now still have these conditions with the bulb limiter in place.
PA1
Negative 12-16 DCmv on output no load
Connecting load results in hum
All PA Vbe look GOOD. Very symmetrical around +/- 590mv.
213mvAC on output no load
Eliminated the bulb and used variac.
-1.5vDC on output as turn up all the way... turned it off quickly and things smell hot.
So I'm quite stuck...again. it's very challenging as the transistor voltages look good.
Oh and -27mv on Q1/2 jfet drains. (Between last opamp and PA).
And U100 (last opamp)
Pin7 -21mv
Pin6 -3mv
Pin5 -3.3mv
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