My fender stage 185 amp won't power up

[spindarec]

so i got to change both before testing if there's more than 1Volt on the main speaker output with a light bulb limiter ?

[Jazz P Bass]

You need to check the transistors for shorts.

Q21 would not blow fuses.
Q15 might if it failed short Collector to Emitter.

[spindarec]

Ok, can i test Q15 still on the board or I've got to remove it ?

[Jazz P Bass]

Look at the schematic.
You tell me.

As there is no direct connection between B C E, probably yes.

It also will depend on the fact that other transistors may be bad.

At this point we still do not know why the fuses are going.

[spindarec]

Look at the schematic.
You tell me.

Noob I am, sorry . Schematic is a bit hard to read for me but I'll try to do my best.
I'll check it tomorrow now, time to sleep for me now. Thank's ´gain for your precious answers and advices.
It really helps.
See ya.

[g1]

a piece of Q21 is broken too. look at the picture.[ATTACH=CONFIG]34011[/ATTACH]

Yeah, it's hard to see from the pic, but his "head is blown clean off" . Not sure what could possibly do that, but that one for sure needs to be replaced.

[Enzo]

Q21 is a mute, and I also cannot think of anything that would do that to it.

On the other hand, just remove it for now, the amp will work without it, well as long as the rest of teh amp is OK. I mean you don't have to wait to order Q21 to finish the repair. Replace Q21 later.

[spindarec]

Hey,
I've changed Q15 by a new one with a good soldering' now.
The main output to speakers shows 0,67V. I build my own light bulb limiter and nothing blows…
What should i do ?
Can I test ?
Thanks.

[Jazz P Bass]

Does the lamp limiter glow when the amp is at idle?

If not, ditch it.
Put a 1 amp fuse in the main fuse holder for now.
If that holds, you will want to make a few CAREFUL measurements.

The main output transistor Base leads (+ & -) should sit at about 0.5 to 0.6 volts.
Measure the output voltage again.
It should be lower.
670 millivolts is high.

Edit: Have you removed Q21?

[spindarec]

what do you mean by " at idle" ? The lamp limiter doesn't glow when the amp is turned off.
I haven't removed Q21.where is the main output transistor ? sorry i'm really a beginner.

[Jazz P Bass]

Well, yeah, the lamp will not glow with the amp off.

Idle is idle.
Like a car.
It's how much current the output section draws without a signal.
The schematic indicates 28 millivolts across R168.

The output transistors (there are 4) are the big silver thingies bolted to the heat sink.
You cannot get to the base pin unless you flip the board over.

So go on Q15's Emitter lead.
You want to see 0.5 to 0.6 Vdc.

Likewise, Q16's Collector lead.

If you are not sure of the lead assignments, look up the transistor datasheet.

[spindarec]

it hold with a one amp fuse.
So i got to put one pin of my volt tester on the base pin of the output transistor and the other pin of my tester to Q15's Emitter lead and then with Q16's Collector lead ? That's it ?
Thanks

[Jazz P Bass]

All voltages are referenced to Ground.

The Red meter lead is the probe.
The Black meter lead can be attached to the chassis.

[Jazz P Bass]

All voltage readings that I mentioned are referenced to Ground.

The Red meter lead is the probe.
The Black meter lead can be attached to the chassis.

[spindarec]

I tested Q15 and Q16 and i got nothing, the same thing for the base pin of the output transistor…
The main output shows 0,76V now…
What happened if i've badly connected CP10 and CP12 ? if i've reversed the wires ?