gonzothegreat
Super Member
This was an amp I found in the dumpster many years ago and after patching up the broken traces, unbending the faceplate and replacing a pile of transistors, its still not quite right.
One channel is fine but the other puts out -53vDC (i.e. the negative rail for the outputs). I've checked every component with an ohmmeter/transistor check function against its mate in the working channel w/o any clue.
I even swapped transistors in the input diff amp with the good channel when I thought the problem might be there (nope). Then I realized the negative feedback line was throwing off my readings. I can't keep it on for too long to do voltage measurements since the driver stages get warm fast.
So here's my question - how can I troubleshoot this kid? Do I stick a cap in the feedback line to filter out the DC or can I disconnect feedback entirely? Or does somebody have a different plan of attack?
Virtu-Al
One channel is fine but the other puts out -53vDC (i.e. the negative rail for the outputs). I've checked every component with an ohmmeter/transistor check function against its mate in the working channel w/o any clue.
I even swapped transistors in the input diff amp with the good channel when I thought the problem might be there (nope). Then I realized the negative feedback line was throwing off my readings. I can't keep it on for too long to do voltage measurements since the driver stages get warm fast.
So here's my question - how can I troubleshoot this kid? Do I stick a cap in the feedback line to filter out the DC or can I disconnect feedback entirely? Or does somebody have a different plan of attack?
Virtu-Al
here is the Service Manual
take care to have a good ground...
