Peavey 260c Assistance/Insight needed.

[Jaxn]

Ive gotten as far as i could using the other posts on here, but have run into a wall.

I got a peavey bass combo off a friend who was going to throw it out.
The amp turned on but made no noise, no hiss or hum.

R23 was burnt out so i replaced it.
Turned on, burnt out again.
Checked and found the v+ and v- were way out.
Replaced the large filter caps
V+ and v- back to normal (+/- 42v with no AC ripple), still burnt out r23

Ive got 23v DC on the output with no speaker connected. Ive gone through and checked all the resistors for opens or shorts. The large .33ohm 10w resistors give me a reading of 620 ohms while in the circuit, but i'll desolder to check thoroughly.

I have a couple years experience with guitar effects and modular synth circuits but this is my first attempt to repair an amp, other than replacing pots and jacks.

[R.G.]

When solid state amps die, they often leave a trail of destruction as the failing part makes something else fail, and that makes even more things fail.

I don't know what "R23" is in that amp, not having the schematics.

If you have DC on the output, and a 0.33 ohm resistor that measures 620 ohms, there is something still seriously wrong. With SS amps, it's not as easy to pinpoint problems as with tube amps. In general, you're probably going to have to measure or replace almost every part. This is not a disaster - there are only 20-30 parts in there. It would be good to make and use a light bulb limiter to keep faults from being destructive while you measure, along as you have the skills to make/use one of those safely. And don't hook a load to it until you think it's working OK without a load.

[Jaxn]

Thanks for the quick reply. I just looked up light bulb limiters and that looks simple to do. After i test some parts removed from the circuit i'll post any findings. Also the schematic is the same one floating around on here for the 260c but i can repost if it helps.

[Jazz P Bass]

10:1 you have a shorted output transistor(s).
That is what is frying R23 (47 ohm on NPN base output transistor) & placing Vdc on the output.
Remove them all.
If you check them with a DVM diode check you will know which ones went south.
Peavey can supply any replacement parts that you will need.
Test the power supply first with the lamp limiter.
There are voltages marked all over the schematic. (Thankyou Peavey!)

[Jaxn]

I checked the output transistors and replaced 2 of them that were fried. I also tested the 10watt resistors and 2 were open, getting replacements in Australia was a mission to say the least.

When i reassemble everything and start it up with the lightbulb limiter the test voltages will be the same and it is the current that is limited? Or is there going to be a uniform drop in voltage across the entire amp?

[Jazz P Bass]

All of the voltages will be lower.
Use at least a 60 watt lamp bulb.
At idle, the amp should not pull more than 60 watts if everything is hunky dory.
That will be indicated by the limit lamp.
Bright until caps charge.
Then a (it all depends on the current draw) relatively dim glow.
I try to monitor whatever I can.
The high voltage rails are a good start.
The more volt meters the merrier.