Re: TOA 900 series ii Amplifier P-912MK2

Update: The secondary problem (faint volume level) was due to a bad integrated circuit M204 in the "'remote master control circuit" of the preamp (a dual OpAmp: NJM4558DD). I detected it using freeze spray. Bought, installed, works, done. The only remaining problem is that I had already purchased a used / identical amp from eBay because we needed it for our church PA system ... so now I have a spare unit that I don't need! Guess I'm headed back to eBay or Craig's list or something.

Re: TOA 900 series ii Amplifier P-912MK2

I wanted to thank you guys for your insights, and perhaps return the favor by relaying my recent experience.

My TOA A-912MK2 amplifier died after a power surge. It was stuck in “protect mode”. Based on Post #2, I found that the idle voltage was +6 Volts instead of Zero (thanks “redwire”!), so the protection circuit was working as designed. Post #6 provided a schematic showing the expected voltages at various transistor leads (thanks “Bterrier”!). So, I worked backwards from the output transistors in the Power...