AMPEG SVT3 Pro Fan and 12AU7 not working

[GainFreak]

Hi,

I have an SVT3 Pro where the fan and 12AU7 filaments are not working. Replacing the tube didn't change anything. Obviously if fan doesn't work the amp wouldn't start either. I didn't dig through the schematic in detail but I suspect amp's input is muted somewhere (there's slight hum at the speakers' output) to prevent overheating. You can see some voltage readings below. F1 fuse is good.
I'm not transistor guy but from what I gather Q17 (TIP32C) is not working. Or 'maybe I'm missing something?

[Jon Snell]

Check F1 and ensure D21 is OK and look at the 65v supply. Is the fan OK. Make sure the 65v is there. Both valve heaters are in series and ignore the fan speed controller as that won't stop the heaters.

[GainFreak]

Fuse is good (not open). 65V supply is there. Fan is working from external power supply.

[Jon Snell]

Voltage of pin 4 of V2?
Voltage on fuse?
Q17 dry joint?

[GainFreak]

Those voltages are on the pic above.

[Jon Snell]

So they are.
I would suggest Q17 is collector emitter open circuit as there is enough voltage to make it conduct.
Have you checked Q17 for continuity and hfe?
Take it out and measure it.

[g1]

Do you measure continuity from Q17 collector to fuse?

[GainFreak]

I checked Q17 with my DMM in diode mode with V1 and V2 out. Readings are as follows:
1 /negative probe on B
B/E and B/C ~570
2/ positive probe on B
B/E - OL (open), B/C starts from 920 and goes up to 1120 which doesn't look right.
Also C/E (-/+) 540, C/E (+/-) OL (open).

[GainFreak]

Do you measure continuity from Q17 collector to fuse?

No continuity from Q17 C to fuse but it's there from V2 pin 4 to Q17 C and from pin 5 to fuse as per schematic.

[Jon Snell]

Always remove the component from the board to test it unless you know exactly what you are looking for.
As Q17s base goes more negative with respect to the emitter, the more the collector will increase in voltage. That is all there is.
Check with another transistor.

[GainFreak]

The way I see it with the tubes out al transistor's pins can be considered "free" which should not affect the measurements unless there's some conductivity PCB problem or something.
I was hoping to avoid removing the whole power amp board but it looks like it's inevitable.

[g1]

If you don't have continuity from pin4 to pin5 it won't work. And by continuity I don't mean a dead short, just the proper expected resistance. Probably a bad solder joint at the socket, or bad socket.
If you were going by a continuity 'beeper', check on resistance range. Compare to pin 4 to 5 resistance of V1, should be similar.

[Enzo]

You mentioned "tubes out". If there is no 12AU7 in the socket there can be no continuity between the fuse and the transistor Q17.

[GainFreak]

You mentioned "tubes out". If there is no 12AU7 in the socket there can be no continuity between the fuse and the transistor Q17.

That's what I said earlier. By tubes "tubes out" I meant tubes "out of their sockets".

[Enzo]

But were the tubes out when you tried to measure the continuity?

With a 12AU7 INSTALLED in V2, is there continuity from Q17 to the fuse?