pioneer a717 help please

mibag6

AK Subscriber
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Hello Pioneer guys. I usually dabble in the tube world but a friend brought over a Pioneer model A717 which has at least one issue, a steady pop, pop, pop on the right channel after 10-15 minutes warm up. I checked DC offset at 2mv on the left and -9mv on the right but beyond that, I'm a little outside my comfort zone here. Any advice on what to look for? There does not appear to be any bias/offset adjustment pots so I'm guessing that's managed by ICs on the amp board.
Thanks in advance for any help you can provide.
 
popping is mostly put down to a bad transistor .
wait for detailed instructions from someone more knowledgeable
 
That's what I was thinking, just hoping to narrow it down a bit. If it helps, he did say that it may have been turned on briefly with the volume control all the way up prior to this behavior.
 
Disconnect the amp from the preamp with the back panel switch. That'll narrow it down a bit.
 
I don't see a switch on the back panel. It does have jumpers in a section labelled ADPT 2 with the RCA inputs on back, I believe these are removed for installing a graphic equalizer. Are they the same as Pre out / Main in jacks?
 
Photos of the main amp, everything else is pretty well buried.
 

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I think I've narrowed it down a bit. It actually goes goofy on both channels but if I defeat the tone controls, all is well, which should narrow it down to the tone amp board. If I read the schematic correctly, ICs 301 and 302 are the only devices common to both channels. 301 is the tone amp and 302 is muting.
Am I on the right track here?
 
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