Peavey session 500 (400 B/Gmodule)

[Sandwich]

Wait, moving back a few posts. You were not trying to power up the board without the large power transistors connected, I hope. Were you? That might explain the 47 ohm resistors if so.

Otherwise those 47 ohm resistors are in series with the 5331/5332 pre-driver transistors.
And that often means they are damaged.

L1 is a small inductor, it will look like a resistor.

The rows of power transistors MUST be connected to the main power amp board.

they were powered up with the powertransistors everything was connected when i power up.

what is it that damages transistors when new have been replaced.

yes i know that small indicators look like resistors but where do you see the difference. i tried to get some pics outa tha komponent that was instead the indicator so you could get a closer look but like my luck is the camera runs outa batteries.

the only difference i see is the form of the thing
http://www.vekoy.com/product_info.php?products_id=8347

[Enzo]

The amp should function without it at least for testing.


When amps blow up, you can quickly find the bad output transistors. You then need to check the drivers. The drivers are the end transistor in each row of four on the power transistor strips. You need to verify that all those large cement power resistors are OK. Check them for open, they won;t be wrong, just OK or open. The predrivers - the ones on the small heatsinks are often stressed by output failures. Those 47 ohm resistors around the 5332/5331s MUST be checked for opens. Make sure R19,20 are not burnt open. MAke sure CR9,CR14 are not shorted or open. CR9 has a 33 ohm resistor in parallel, so that is what an ohm meter will read. You may have to unsolder it to test. CR14 is a dual diode and on diode test, it shows twice the normal diode reading. Again, check for not shorted or open.

When it keeps burning up parts, it is because the repair was not completely done.

Work without a speaker. Once the unit no longer blows fuses, and doesn;t draw excess current from the wall, look at the DC voltages on the schematic and verify them on your unit.

Q1, Q7 are limiting transistors, and CR10,15 arewhat connects them to the circuit. Check the transistors. Unsolder one end of each diode and lift it from the board, that eliminates those two circuits as trouble. We reconnect them later after testing.

Once all that stuff is OK, the amp output should be stable. Not blowing fuses. Hopefully no DC in the output. If that is the case, then we send a signal thro0ugh and see what happens.

[Sandwich]

The amp should function without it at least for testing.


When amps blow up, you can quickly find the bad output transistors. You then need to check the drivers. The drivers are the end transistor in each row of four on the power transistor strips. You need to verify that all those large cement power resistors are OK. Check them for open, they won;t be wrong, just OK or open. The predrivers - the ones on the small heatsinks are often stressed by output failures. Those 47 ohm resistors around the 5332/5331s MUST be checked for opens. Make sure R19,20 are not burnt open. MAke sure CR9,CR14 are not shorted or open. CR9 has a 33 ohm resistor in parallel, so that is what an ohm meter will read. You may have to unsolder it to test. CR14 is a dual diode and on diode test, it shows twice the normal diode reading. Again, check for not shorted or open.

When it keeps burning up parts, it is because the repair was not completely done.

Work without a speaker. Once the unit no longer blows fuses, and doesn;t draw excess current from the wall, look at the DC voltages on the schematic and verify them on your unit.

Q1, Q7 are limiting transistors, and CR10,15 arewhat connects them to the circuit. Check the transistors. Unsolder one end of each diode and lift it from the board, that eliminates those two circuits as trouble. We reconnect them later after testing.

Once all that stuff is OK, the amp output should be stable. Not blowing fuses. Hopefully no DC in the output. If that is the case, then we send a signal thro0ugh and see what happens.

one dumb question: does a open resistor mean that there comes out more ohms than its ment to be?

R 19 and 20 are OK. R19 was 1.9k ohm and R 20 also 1.9k ohm. so both were very close to 2k ohms.

where can i find a CR14 i dont find it anywhere?

[Enzo]

Electricity needs a complete path. For example from a battery current comes out one end, flows through wires and whatever and back in the other end. That makes a circuit - like a circle. If that path is broken, we have an open circuit.

Turn your meter to ohms, don;t connect the probes to anything. The reading you see is an open circuit. Now you connect a resistaor across the probes and the circuit is closed, and a resistance reading results.

If you read a resistor and the reading acts like there is no resistor there - like your probes were detached - that is open. if the part is soldered onto the boasrd, then other parts on the board offer paths for the current. SO sometimes you must remove the part to truly measure it.

1.9k is more than close enough to 2k.

CR14 is on the heat sink, probably sticking through a little hole.


And if a resistor shuol;d be 100 ohms but measures out at 500 ohms, it isn't open, but might as well be, it is certainly not right.

[phylomatic]

Hey man, check this thread. It could very well be the old peavey speaker if your still using the original Black Widow. My amp didn't work for years and I have a Session 500 and all that was the problem was this stupid issue with the speaker. Easy, easy, easy fix for me, but you may have some serious issues since you've been changing out parts. But definitely check this because the speaker is so easy to maintenance.

http://music-electronics-forum.com/s...ead.php?t=7948

[Sandwich]

thanks for the reply.

My black widow is ok and living. its the preamp 400 b/g module that i have the issue with and its transistor 5331 that i have to change cause it propably has been damaged trough heat. so ill go and get some new ones and mount them in heat sinks before i solder them. it always was the resistor before the transistor that fried. But its a shame that you cant get exact the same transistors anymore, you only get replacing parts.

[Enzo]

Well, the amp is 30 years old after all. Peavey no longer has 5331/5332?

One beauty of solid state amplifiers is that you can substitute transistors VERY liberally and they still work just fine.

[Sandwich]

Well, the amp is 30 years old after all. Peavey no longer has 5331/5332?

One beauty of solid state amplifiers is that you can substitute transistors VERY liberally and they still work just fine.

thats very true

[Sandwich]

Ok some progress...
i found out that the half of the outputboard is active wich means that those 10w resistors on the one side gets hot (R65 R64 R61 R63). Also R 45 and R 46 go hot to on the 400 B/G module. also R61 on the 400 B/G module fries as usuall but not so bad as i use to in the begining.
So ideas are very much welcome.

[Sandwich]

everything works now except when the autoformer is connected then i start to smell something frying

[Enzo]

Nothing wrong with running without the autoformer, after all most models using the 400B/G didn't include it.

Meanwhile, the autoformer may well be shot.

test it like any other transformer for shorted turns and for turns shorted to frame.

Go over to RG's Geofex site and look at his transformer tester. Very simple to make.

[Sandwich]

yes the autoformer is D E A D.

so time stands still until some ideas come up how to bypass the autoformer or get it repaired or ... get a new autoformer.

[Enzo]

COntact the parts department at Peavey and ask them if they still have the autoformer. Get the part number from the schematic. Looks like DG117.

Or don;t use it. COnnect the speakers direct to the amp.

[Steve Conner]

You probably have a DC offset, and that's what fried the autoformer and resistors. Transformers like getting DC shoved through them about as much as cats like getting a bath.

Unless the amp had a big DC block capacitor before the transformer that would block any offset. There are quite a few SS amps that just refuse to drive a transformer without this cap, but it's the kind of thing I'd have expected Peavey to engineer out.

[Enzo]

Or when the amp was blown it destroyed the autoformer, which now objects when you connect it to a working circuit.

The 400B/G is extremely similar to the 400BH, and PV used them in many amps models. The autoformer was only an option added in certain amp models. No output cap, just a straight basic quasi-comp output stage. The only consideration on the circuit board for this is there are two sets of speaker connection posts in parallel, with a idler jumper between two otherwise unused pins. Plug a speaker across the two live pins, or plug an autoformer on there and add an impedance tap wire for another speaker jack.