Picked up a 2238B in decent cosmetic shape with a cut power cord. After powering it up on a DBT, relay clicked. I noticed left channel distortion and loud popping, right channel is good, no distortion and good sound.
After a dioxit to all switches bias and dc offset was attempted, NO bias on left channel but DC was adjustable, right channel could be adjusted properly for bias and dc offset.
I suspected the left channel differential pair, but both left and right voltages on Q701/703 and Q702/704 seem to read ok: C= -36V, E= 0.6V, B= 0V. Found a driver PNP Q709 read open and replaced the pair with an NTE equivalent, Q701, Q703 tested ok with a diode test when I pulled them. R759 150Ω read open and was replaced.
I pulled the outputs and they all tested good with the exception of the left channel PNP 2SB541 which I replaced with a supposedly equivalent sub (ECG285) that came out of my Marantz 2245. Have an NEC 2SB541 coming.
It now has a strange pulsing/soft popping sound on left channel, a little hum present, but no loud popping still distorted. Right channel still sounds good, doesn't go into protection.
Where do I go from here? The differential pairs are still suspect.
After a dioxit to all switches bias and dc offset was attempted, NO bias on left channel but DC was adjustable, right channel could be adjusted properly for bias and dc offset.
I suspected the left channel differential pair, but both left and right voltages on Q701/703 and Q702/704 seem to read ok: C= -36V, E= 0.6V, B= 0V. Found a driver PNP Q709 read open and replaced the pair with an NTE equivalent, Q701, Q703 tested ok with a diode test when I pulled them. R759 150Ω read open and was replaced.
I pulled the outputs and they all tested good with the exception of the left channel PNP 2SB541 which I replaced with a supposedly equivalent sub (ECG285) that came out of my Marantz 2245. Have an NEC 2SB541 coming.
It now has a strange pulsing/soft popping sound on left channel, a little hum present, but no loud popping still distorted. Right channel still sounds good, doesn't go into protection.
Where do I go from here? The differential pairs are still suspect.
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