GK 1001RB no output

[MarkusBass]

Lowell,

I would check the other leads of D12 and D1 - there should be +-43V. If this is true, still the problem can be either in the servo or the input stage. I would check both but I suspect rather the input stage. Have you noticed that several resistors in the amp are marked as FUSE? Especially resistors in emiters of Q10, Q14, Q8 and Q11. If for example R33 (emiter of Q14) is broken, you may have symptoms like you've just measured. You also have voltages on these resistors specified on the schematic so I suggest to check them.

Marek

[lowell]

Markus I had previously replaced those "fuse" resistors and I just tested them, they're still good. the other leads of D1 and D12 are good i.e. around +-40VDC. I do however see that the voltage drops across those "fuse" resistors are not there... it reads 0v on my meter.

[lowell]

I tested D9 and D5 with regular v-drop test and D5 tests good but D9 tests good in forward biased direction and 1.9v in reverse bias direction. This is bad right?

[Enzo]

Lift it from the circuit to test it. That eliminates any false current paths fooling your meter.

[lowell]

Marek, I rechecked Q12 and it tested bad so I pulled it. Guess what I found... on the side opposite my point of view when troublshooting this amp, the other side of Q12 had a big chip missing out of it. I must've installed a bad replacement AND/OR screwed it up somewhere amidst troubleshooting this thing. Anyway D9 is fine after pulling and testing it, I threw a new Q12 in there and voila! I biased things via J5 to 10mv and am letting it sit for a while and monitoring the bias, then I will retest w/ speaker and reassemble. I already connected the woofer and tweeter, both work. I'm very excited it has taken me a YEAR to fix this thing. Enzo, Marek, everyone, thanks so much for your input. I learned alot from this amp and most of all from everyones selfless help here on the forum. Cheers!

[Enzo]

Great! COngratulations. Learning is the best part.

[MarkusBass]

Lowell,

I'm glad you fix it - congratulations. If you now try to reverse engineer the problem, it seems that the problem could be diagnosed and quickly fixed by measuring voltages accross fuse resistors in the input stage and by measuring voltages between emiter and colector of Q12 (servo). We all learn all the time .

Regards,
Marek