[Amps] Alpha 87A - strange power related issue

[Eric Dobrowansky]

I did some further troubleshooting last evening. After ruling out the power switches and the adhesive under the 1000uf cap on the ac input board,  I determined the return path of the relay was not being opened. I then moved on to the control board.

Sure enough, after some measurements, I determined the negative return path at the control board connector was not switching properly upon power down. I suspected the transistor or optoisolator on the AC relay's return (-) side, but while doing some troubleshooting measurements, I must have disturbed something, and the issue resolved itself. No apparent cold solder joints were found. I suspect either there was some leakage via dust buildup, or possibly one of the ferrite beads on the leads of the transistor was conducting. I did move the transistor slightly while testing it.   

So far, as of today, after repeated cycles of connecting the AC power cord, and power cycling the amp, everything is working normally. Worse case, if it occurs again, I will look to replace the opto and transistor.

Thanks again for all the suggestions.

PS - If the Alpha 87A IO list moderator is monitoring this thread, maybe you can approve my membership request. It's been pending approval for a few days now.


Eric
K2CB