tabpat
Member
I took on a project (pardon the pun) for a friend of mine who is trying to get his brother's old Project One Mark III stereo working again and surprise him with it. He initially told me it was "blown." Honestly, I couldn't find any issues other than really grubby switches and frozen meters. Anyway, I recapped the PS and amp/preamp, deox'd it and it sounded reasonably good. Then it sat for a few weeks until he could pick it up. He was on his way over and I plugged it in to make sure everything was OK. After a few minutes, it started to make very loud shot noises. I decoupled the preamp from the amp and it continued to do it. So, out comes the amp boards. I figured that it was most likely one of the small transistors on the board - (2SA750) which I replaced with KSA992s. The good news is that it took care of the shot noise issue. The bad news is that it now goes into protection mode at anything above 5 watts or so where as before it would crank pretty loud.
There are no manuals for this so I'm flying blind. I checked the bias across the resistors and set them at 15ma. The DC voltage is wandering a bit, but is hugging real close to 0mv +/- 3mv - checked at the speaker terminals which I'm not sure is the correct way. Any ideas?? I'm just guessing at this point!
There are no manuals for this so I'm flying blind. I checked the bias across the resistors and set them at 15ma. The DC voltage is wandering a bit, but is hugging real close to 0mv +/- 3mv - checked at the speaker terminals which I'm not sure is the correct way. Any ideas?? I'm just guessing at this point!
