I have this amp and its starting to have me chase a little tail. This amp being the last of a pile of Orions I've been working through; cant imagine why this one I'm getting stuck on.
TO start, this amp has the most resistors that are slightly discolored. Some opened up as well. Most of the darkened resistors changed only about 10% so I'm leaving those in for now until I find the real fault still at hand.
I had to replace 6491s on one channel and 6488s on the other channel. The channel with the 6491s I replaced is causing excessive draw across those 6491s.
I'm seeing 0.006vDC across the new 6491 emitter resistors (Three bottom/middle of photo). and 0.000-0.001vDC across ALL other emitters of both channels.
Tracing back through the circuit I tested but still replaced several MPSA06/56 drivers still nothing solved.
I then found both 5.7ohm 1w resistors on that channel failed near the new 6491s (Bottom left of photo). One opened up and the second was measuring 100kohms, so I replaced both of those with temporary 3ohm series pairs to 6ohms 1/2w to keep troubleshooting for now. That didn't help.
I then replaced the one 6491 and the 6488 nearest to the front of the amp (Bottom left of photo). I'm presuming those are being used as in the output section as drivers/bias and/or voltage regs.
To compare I also have a working XTR250 I've been referencing but so far everything is measuring well.
I'm a bit stumped at the moment. Any pointers perhaps?
TO start, this amp has the most resistors that are slightly discolored. Some opened up as well. Most of the darkened resistors changed only about 10% so I'm leaving those in for now until I find the real fault still at hand.
I had to replace 6491s on one channel and 6488s on the other channel. The channel with the 6491s I replaced is causing excessive draw across those 6491s.
I'm seeing 0.006vDC across the new 6491 emitter resistors (Three bottom/middle of photo). and 0.000-0.001vDC across ALL other emitters of both channels.
Tracing back through the circuit I tested but still replaced several MPSA06/56 drivers still nothing solved.
I then found both 5.7ohm 1w resistors on that channel failed near the new 6491s (Bottom left of photo). One opened up and the second was measuring 100kohms, so I replaced both of those with temporary 3ohm series pairs to 6ohms 1/2w to keep troubleshooting for now. That didn't help.
I then replaced the one 6491 and the 6488 nearest to the front of the amp (Bottom left of photo). I'm presuming those are being used as in the output section as drivers/bias and/or voltage regs.
To compare I also have a working XTR250 I've been referencing but so far everything is measuring well.
I'm a bit stumped at the moment. Any pointers perhaps?
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Fixed. Ultimately some of the new parts were getting fried as I was finding more failed parts. Eventually (And about about ~4 MPSA56 burn-outs) I found the culprit. In fact it was everything listed out in post #1, I had just failed to re-check some of the newly replaced/poped MPSA56.