Evil Twin question

[drewl]

In the low power mode of this amp, it doesn't seem to be channel switching properly: IE: both channels are active instead of switching between the two.
( yes I'm using the switching inputs not the parallel inputs)
Am I correct in thinking this ain't right?

just curious before I crack her open
Any schematics floating around for this?
---got the schematic---
I promise to look befor asking next time.

Thanks.

[Mark Black]

I've got a .gif file, the only one I've ever found, and it's not too bad.

Too big to upload here apparently. Send me a PM with your email addy and I'll send it to you...

[Rob Mercure]

Drewl,

I haven't been into one of these in a while but if we're referring to the same model - red knob? - the PS PCB in the center has two large resistors, cylindrical, not square and perhaps 20W, that provide the low voltages for the semiconductors and such. Unfortunately these resistors "brute force" large dissipation and too much of this dissipation occurs in the resistors leads and they "unsolder" themselves from the board. If you've got the unit open - unpowered - and you can wiggle these then that's part of your overall problems if not the answer to the specific. After working and reworking one particular amp that liked returning to the shop I wound up folding a piece of sheet copper over each resistor's lead - they're quite long to provide air flow - and after soldering these heat sinks to the leads I popped a rivet in there just in case that my copper heat sink unsoldered itself. The amp never came back so "no news is good news."

Rob

[drewl]

Thanks Rob, I figured it has to be something like that, pretty common.
I thought it odd that in high power mode it's fine, but after looking at the print, lo pwr mode lowers the voltage, which is prolly screwing with the power supply for the switching circuits.

thanks again.