Peavey CS400 repair

[ret7772u]

I have this OLD CS400 with one channel out & blowing fuses when I hook up the power to that board. I read here that it is prolly a shorted power transistor & I should be able to replace them.

My question is: there are 3 different numbers on the transistors:

SJ6344 (2 of them)
2N3773 (2 of them)
SJ6337 (4 of them)

Basically I know how to solder real good - so I don't know if all of these are different part #'s for the same transistors or if they each are different in design & function.
After a search on the internet - I could only find any info on the 2N3773's & a noticible lack of info on the others.

I would appreciate some info on these issues from one of you brilliant minds out there - so far your advice has got me to the prob - now I need to fix it.

Thanks

[Jazz P Bass]

Remove all output transistors on the failed side. They are in parallel. Check each one with a DVM on diode check. Find the shorted one(s).
Those SJ numbers are Peavey internal part #'s.
Call Peavey. They have the right parts, schematics & tech help.
ps: I repaired one of these where a capacitor on the bottom of the output board was shorted.
I still had to remove all the output transistors to find it.
Happy hunting!

[Steve Conner]

I'm no expert on these amps, but I don't believe they should have 2N3773s in them. They're 140 volt transistors, which is a bit too low for a 200 watt amp. Someone probably bodged it, and the 2N3773s blew up after a while. The Peavey house numbers are just Motorola (now ONSemi) power transistors, I believe they're MJ15024 and MJ15025, or MJ21194, MJ21195 or whatever. Even if only one device in a bank has shorted, it wouldn't hurt to replace all four.

But don't take my word for it, take Enzo's This has been discussed before so try searching the forum. And watch out for fake transistors when you're buying.

[ret7772u]

Hmmmm... the 2 2N3773's are marked Toshiba & all the rest are indeed Motorola transistors. Looks like the 2 Toshiba have been replaced. If these are underpowered - what is a good replacement?

[Steve Conner]

Oh, my bad, I dug around a bit and found the Peavey cross reference guide. SJ6344 is some sort of driver transistor, which is supposedly obsolete, but it crosses to peavey part # 70481140, which is a 140v NPN driver transistor.

So that leaves you with two 2N3773s and four SJ6337s that are presumably the output devices. SJ6337 isn't even in the peavey guide, but you probaly read it wrong. Read this thread on diyaudio carefully from top to bottom

diyAudio Forums Archive - Peavey CS-400 Schematics Wanted

and get back to us.

Executive summary: I think Enzo said somewhere in that thread that you can replace the whole lot with MJ15024s.

But anyway, you might as well get all the transistors out and check them with the diode test on your meter to find any shorted ones. Check to see if the amp has the crowbar triac and whether that's shorted, too.

[ret7772u]

Yup..read it wrong - it's SJ6357 not 6337. I found a cross reference number that is 'sposed to be the sub for it 12701785 (actually it first said 70484140 - then gave me the 12701785 as the sub for it).

I'd like to replace all 16 or at least the 8 for that channel - but I don't have a clue where I could get them - not the sort of stuff i order very often.

[Steve Conner]

Well, this thread and the DIY Audio thread already mentioned several sources.

First off, you may still be able to buy them direct from Peavey. Supposedly their support is pretty good, and if you do this you know you're getting the right parts. Peavey say that they select transistors for beta and so on.

Second, most big electronics distributors should carry the MJ15024. Allied, Mouser, Digikey, and so on, for 4 dollars each or so. It's not an exact replacement for the trannies in the CS400: it's an extra burly part that's actually overkill for the job.

[ret7772u]

Thanks guys - I'll let ya'll know how it works out. This forum is a goldmine of info!

(That's right - I said ya'll - it's true...I'm from Texas!)

My grandfather always said: "Never ask a man where he's from - if he's from Texas, he'll tell you; if he's from anywhere else...don't embarrass him!"

[Enzo]

Hi. I know I posted the PV semiconductor cross reference before. Search for it here.

AS mentioned above, the end transistor in each row is a driver, not a output. If you look at the traces on the board you will see that one is different. That is the SJ6344. PV crosses it to their 70481180. The SJ6357 is the cross to the 70484140. ALL of those are Peavey house numbers, not industry types. You won;t find a data sheet for SJ6357, but you will find it for MJ15003.

The 6357/84140 is an MJ15003. I buy them from Allied myself - I get most all my Moto transistors there. In a pinch you could replace a 6344 with the 15003 as well. But the 6344 is really an MJ13330.

The power rails in this thing are +/-59VDC, so 120v across the output. 140v parts would be just OK. But it is what PV used.

On each module, there are 8 power transistors. They are not all in parallel. There are two rows of four. One row is for the +59v rail , and the other row for the -59V rail. In each row, the end part is a 6344, with three 6357s in more or less parallel. I agree with taking each out and checking for shorts. Most times it will be one shorted one on each polarity row. But sometimes more than one. Gotta find out.

Take them off the board for testing, ther are low value resistors across them that will fool your meter.

Once you have weeded out the shorted ones, see what is left. If a driver is bad, replace it. Any good outputs can be reused.

Here is a caution. The three parallel output transistors on each side must share current, and track thermally - they have to work together. TO do that, they must all be the same part. And they need to come from the same manufacturer. PV did use some 2N3773 as 84140s, and they were Motorola(which is now called On Semiconductor). 2N3773 from two different companies - like Moto and Toshiba - may have similar specs, but they are made on different lines by different processes. They will not be the same.

What you don;t want to do is mix parts. You want all three on a row to be the same thing. Now the Moto MJ15003 and the Moto SJ6357 ARE the same part. But the 2N3773 is not the same as a 6357. And the Moto and Toshibas are not the same either. You can use any part you want that meets the spec, just use three of them. DON'T MIX.

It really doesn;t matter if the ones in the positive row match the ones on the negative side. SO three of one on one side and three of the other on the other. Just make the three on a side match. SOmetimes we pull a good one from the other side to make three, and replace all three on the other side.

And yeah, I do think of the MJ15024 as the sort of Swiss Army Output transistor.

PV will sell parts direct, and their prices are not outrageous.