Ampeg SVT-6 Pro No Output

[g1]

Sorry but I don't think I will be able to contribute any useful ideas on this one. I don't work on them.

[ca7922303]

Sorry but I don't think I will be able to contribute any useful ideas on this one. I don't work on them.

You did say that in the beginning I remember. I appreciate you helping me get this far. I think I'm about there, just gotta get 2nd amp right. Thanks.

[nosaj]

I will say I'm not super versed in transsistors but when you have the same voltage across all 3 legs its not a good sign. Check q1 and q18 out of circuit.
nosaj

[ca7922303]

I will say I'm not super versed in transsistors but when you have the same voltage across all 3 legs its not a good sign. Check q1 and q18 out of circuit.
nosaj

I replaced both Q1 and Q18 previously. Today I swapped C34/37 for C6/C7 with no change in readings. I've gone all over this schematic trying to find why Ch 1(+) is now correct and Ch 1(-) is still not correct. Here are readings on IC1/IC2

IC1:
1(-1mv)
2(-1mv)
3(0mv)
4(5v)
5(243mv)
6(245mv)
7(0.5mv)
8(5v)
9(5v)
10(0.6v)
11(-7v)
12(-1mv)
13(0.5v)
14(-1mv)

IC2:
1(-4mv)
2(9v)
3(1mv)
4(-12mv)
5(1mv)
6(1mv)
7(1mv)
8(7mv)

All readings are taken with variac @ 20vac to try to prevent damage to mosfets while locating components causing voltage difference on gate busses.

[ca7922303]

I will say I'm not super versed in transsistors but when you have the same voltage across all 3 legs its not a good sign. Check q1 and q18 out of circuit.
nosaj

I've actually replaced all Q transistors except for Q3/4/16. Q3/4 have the gate busses correct on Ch 1(+) and Q16 looks like it is controlling fans.

[ca7922303]

I will say I'm not super versed in transsistors but when you have the same voltage across all 3 legs its not a good sign. Check q1 and q18 out of circuit.
nosaj

Have also replaced every diode connected with mosfets, and all resistors connected to mosfets are correct.

[nosaj]

Ok so I still suggest you pull those 2 an test them out of circuit.
nosaj

[ca7922303]

Ok so I still suggest you pull those 2 an test them out of circuit.
nosaj

Q1 Base-Collector(0.6v) Base-Emitter(OL) C-E(OL)
Leads reversed (OL/OL/0.6v)
Q18 b-c(0.6v) b-e(OL) c-e(OL)
Leads reversed (OL/OL/0.6v) diode test.

[ca7922303]

Replaced IC1/IC2 . Voltages have changed some on those two, but no change on Ch 1(-) gate busses.

[ca7922303]

Replaced all diodes associated with Ch 1(-) board, no change in gate buss voltage.

[ca7922303]

Ok so I still suggest you pull those 2 an test them out of circuit.
nosaj

What do you make of the Q1/Q18 measurements out of circuit?

[nosaj]

What do you make of the Q1/Q18 measurements out of circuit?

Let me flip it. What do you think of the measurements?
nosaj

[The Dude]

What I think is that you have the transistor legs mixed up. Otherwise, your readings make no sense at all.

[nosaj]

Is Q18 a 2n3440?
nosaj
https://my.centralsemi.com/datasheets/2N3439.PDF

[ca7922303]

Is Q18 a 2n3440?
nosaj
https://my.centralsemi.com/datasheets/2N3439.PDF

Yes, Q18 is a 2n3440.