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In Reply to: RE: Help with Rotel RB-990BX! posted by Roypercy on October 18, 2016 at 11:25:58
I fear you've taken out a channel on the amp.
As for the preamp, swap cables left to right and vice versa to the power amp - this time with everything powered down!
Does the missing channel change or does it stay the same? If it stays the same, chances are the problem exists with the power amp.
Follow Ups:
Hey, thanks for the response E-Stat!
Yeah, I tried that. It stays the same. There's no sound coming from the left speaker output on the amp, regardless of the orientation of the outputs from the pre.
So if I've taken out the left channel, what kind of repair are we talking about? Is it outputs, or something more complicated?
Do any of the .22 ohm resistors look burned? If you have a voltmeter, check the DC voltages to ground on the fuses that blew. Looks like 10 output transistors per channel, separate windings and associated protection and rectification diodes for each channel. You might have gotten lucky and diode went before the output transistors, or some outputs failed and one of the diodes...
10 output transistors!!! Wow. If you blow one are you going to have to buy a matched set of 10 new ones?
Good question. Times have changed, semiconductor processes have improved, variances are typically a lot less. Order the same brand as the transistors that are in there and you should be fine. This isn't universally true, but the service manual for this amplifier is very good and there is nothing noted about selecting or matching these devices.
if the fuses remain intact, then I suspect you'll need to service it.
FWIW, I found the following thread about someone else who lost their left channel with one over at the Polk forums. Don't know if any information presented there might be helpful.
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