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I lifted the legs on d9 and d10. No change

Working on a PL400 (different than the one with the DBt issue) and would like to replace the Q1 and Q2 TIS97 transistors as recommended by the manual to correct high DC offset. Mouser and Digikey both list the TIS97 as obsolete. Although Mouser lists a substitute, the specs for the sub don't...

Good thought, that would explain the problem being on both channels. I'll give it a shot, Thanks for the idea!

Has me befuddled too.

I tried that when I removed the pots... I also checked the jacks, and they test fine as for grounding and connectivity.. sigh, I've hunted the schematic, and don't find any clue. Another cup of coffee, another pondering session.

Thanks George!

Done. No change... I even swapped out the bottom row with tested and matched 410's. I'm at a loss.

I taught myself everything I know... and I still don't know anything! I brought it up that way, but I did not have the speakers hooked up, so I had no indication of trouble. I'll try it in reverse as you suggested, this time with speaker testing. Thx Gene.

Well, that wasn't the problem. dbt still lights up with speaker hooked up.

nice!

One further consideration. The previous owner wired in a couple of input potentiometers ala Series 2. I didn't mention them as I assumed the Amp was working prior to losing some transistors. Here are some pictures, I somewhat wonder if the input/output wiring is incorrect? I would remove them...

it is not channel specific, a does it with either left or right speaker connected individually or together

no sir

OK, I brought the Variac up to 45V, and the output reading was at 7 volts. It was rising as I increased the voltage from the variac. Just to double check, I disconnected the speakers, and the out put voltage dropped to .05V with the variac all the way up to 120V. BTW, I have a volt meter inline...

I'll do that if you think it's ok to run it with the bulb lit? The variac wont do above 70 Volts due to the draw when the speakers are hooked up.

Well, still the same. hmmm

I'll give that a shot. I haven't installed the Output Relay yet. I am hoping to have the unit sorted out before making changes.

nope To simplify the issue...whenever I hookup speakers, the DBT lights up.

Still wondering if anyone has suggestions.. grounding seems fine

Thanks for the idea, I'll check that out. Long term I might WOPL this one, but the board looks nice for now. With every measurement checking out that I described, I'm willing to bet it is something simple. Too simple for me. LOL