Peavey 400B module troubleshooting

[Emanuele]

Hi!
As suggested by Enzo I started a brand new thread in order to ask an help for my new repair project. (and yes it's not a 400BH module as I wrongly said in the other thread)

It comes with a Peavey Mark III bass head that I bought as broken on ebay, the fuse was missing and the fuse holder was bypassed by someone at some point...

After some rewiring and before I powered it for the first time I checked all the output transistors (since for my small experience that's one of the most common causes of fuse blowing) and one was shorted indeed. I put a whole set of new transistors (mj15003g) and BANG! R61 (the emitter res of the lower driver) was burnt. So I checked the drivers, they measured good, but since I broke one of them while I was putting it back on the PCB, I bought a new pair. I tried to power it up (just in case I was missing something on the old pair) but obviously, r61 went on fire again.

So, what to look at now?

I got some pics of the inside, in case I'll upload them in the next post..everything looks fine BTW and the connections on the module are matching the marks that someone made before me (dots and numbers, dunno if it's something that came straight from peavey)


THANKS,

Ciao!

E.

[TigerAmps]

Please post schematic so we are all on the same page ...

I think there were 400 BH's with and without the fuses ...

On my schematic (with the fuses mounted on the board) R23 is a 2.7K resistor. Is that what you are talking about?

[Emanuele]

Please post schematic so we are all on the same page ...

I think there were 400 BH's with and without the fuses ...

On my schematic (with the fuses mounted on the board) R23 is a 2.7K resistor. Is that what you are talking about?

No, mine is a 400 B/G, the fuse comes with a fuse holder mounted on the chassis..

[TigerAmps]

So there are no fuses on the rear board?

Is this what you have? (R23 is still a 2.7K resistor)

Bass MK III.pdf

[Emanuele]

So there are no fuses on the rear board?

Is this what you have? (R23 is still a 2.7K resistor)

[ATTACH]38549[/ATTACH]

yes! that's mine! and I was going wrong by mind, the resistor I got burned is R61!

[Enzo]

Look up light bulb limiter, make one, and use it.

Until we KNOW the amp is stable and not producing DC on its output DO NOT connect a load to the amp. I don't think the bass version of the 400B/G has that impedance transformer, but if it does, disconnect that also until we are fixed.

http://bmamps.com/Schematics/Peavey/..._Schematic.pdf

47 ohm R61 is the collector resistor of Q12 and also the base resistor of Q13

[Emanuele]

Look up light bulb limiter, make one, and use it.

Until we KNOW the amp is stable and not producing DC on its output DO NOT connect a load to the amp. I don't think the bass version of the 400B/G has that impedance transformer, but if it does, disconnect that also until we are fixed.

http://bmamps.com/Schematics/Peavey/..._Schematic.pdf

47 ohm R61 is the collector resistor of Q12 and also the base resistor of Q13

Ok! The light bulb limiter was something already on my to-do-list, so I'll make one asap.

Once I've got it, what should I do next? I suppose, i could put back R61, power up the amp (with no load as you suggest), and then check voltages safely without anything going on fire?

thanks again guys!