Peavey XR-400 Amp section burned circuit indentify

[Darindanford]

Hey guys, wondering if anyone could help identify the resistors and other circuits fried on this board.
And any advise on what to swap out so this doesn't happen again.

[Jazz P Bass]

And any advise on what to swap out so this doesn't happen again.

What a statement!
The amp was built in 1979.
There is a long list of possibilities of what happened to this amp.
None of them includes faulty design.

Anyway, I have attached the power amp schematic.
What you have there is the 200H Rev A.
I do not have the board "Layout' diagram, so you will have to trace things out to see exactly what blew up.
It appears that you had one or more output transistors fail (for whatever reason) & the driver transistors also went up.
You will have to check all of the associated resistors & diodes in that area as the failure current appears as if it was pretty severe.
Also, all of the carbon will have to be scraped off before you install new parts.

[Darindanford]

What a statement!
The amp was built in 1979.
There is a long list of possibilities of what happened to this amp.
None of them includes faulty design.

Anyway, I have attached the power amp schematic.
What you have there is the 200H Rev A.
I do not have the board "Layout' diagram, so you will have to trace things out to see exactly what blew up.
It appears that you had one or more output transistors fail (for whatever reason) & the driver transistors also went up.
You will have to check all of the associated resistors & diodes in that area as the failure current appears as if it was pretty severe.
Also, all of the carbon will have to be scraped off before you install new parts.

Thanks for the schematics.
Sad to say that I wish I was an electronics engineer, so without a diagram of the parts and what they are, I am lost.

[Jazz P Bass]

Peavey 200H A Schematic

I searched further and found a layout diagram.
I have also included the cross reference for Peavey's part numbers.
Identify what is torched & we will take it from there.

[Darindanford]

ROCKIN!!
Thanks that's just what I needed!
I don't know where you found that, I looked everywhere!

[Enzo]

I bet you didn't look at customer service at Peavey. They have it, and will always send it to anyone who asks.

[Darindanford]

Ok, I just received the parts that I ordered from various places.
What I replaced:

Q7, 8, 9,10
Q4 (which was fried)
CR3, 4,8
R12 (which was fried)
R13 (which was fried)
R16 (which was fried)
R17
R19, 20,22,23,24

And plugged everything back in la low and behold,
R21 and CR10 lit up like a blaze!

What did I miss?

[Enzo]

You missed the part about looking up light bulb limiter, then making one and using it. I know, we hadn't mentioned it, not your fault.

Always work WITHOUT a speaker load until the amp is stable.

Look at the amp in vertical stripes. Recheck the four outputs for shorts, Q7,8,10,11. and the five resistors for opens. The two clamping diodes CR10 CR11 almost never fail, but you can check them for shorts..

Now move a step left, drivers Q6 Q9. Recheck them for shorts. Well check them in general, opens can be just as harmful as shorts. I see a 10 ohm and three 47 ohm resistors. They OK? If E21 burnt then almost certain either Q9 or Q10 is bad, they are the only paths current has through that resistor. CR9 runs between Q9 and Q10. is it OK?

Now check the 100 and 120 ohm resistors in the middle.

Next Q4 Q5. They are limiters. We do not need them during test. Disable them by lifting each ones diode from the circuit. CR4 CR8.

Left more and e have the extremely important bias string. Four diodes CR3,5,6,7. Note CR5,6 are really one part - a dual diode. I am not so worried any of them are shorted. If one shorts, it makes the amp run cooler and increases distortion a bit. But it won't blow fuses. But if they go open, then the amp can burn up. SO check them all, and the 1.5k R11 below. And see 2.7k R26 nearby? Check it. CR7 has a parallel 22 ohm resistor so will appear shorted. Note CR5,6 is poked through a little hole in the heat sink. make sure it is not touching the leads to anything.

While we are on this bias circuit, don't overlook the top end, Q3 R9 and CR1,2.

I canbelieve R21 burnt up, but it is right next to CR10, but totally unrelated. Are we sure CR10 wasn;t just a bystander?

At this point, anything farther left can send the output over to one of the DC extremes, but without a speaker load, they won't cause things to burn up. SO your problems I believe are from the CR3,5,6 point to the right side.

And way over to the right at the output is 22 ohm R25. Check it for open.

[johnagape@comcast.net]

Where did you order diodes and resistors from can't find parts anywhere

[johnagape@comcast.net]

This thread has helped alot but can't find where to order parts from.

[The Dude]

You might think about adding your location to your profile so we know what part of the world you're in. It's hard to recommend parts sources without that information.

[Enzo]

Comcast is a USA ISP, as far as I know, so likely USA.

You can get any part for Peavey product from Peavey. The special dual diodes (13886?) is best got from them, though other Peavey parts suppliers probably sell them. Anything else is common. Peavey puts house numbers on lots of transistors, so SJ6357 is a MJ15003 or some such, and hte little 5332 are some generic I forget at the moment. Peavey has a master semiconductor cross reference they will send you.

Or here;

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

[HardyKefes]

Hello, I have XR400 and got the diagrams. However, My amp is equipped with 4x2N5633, the diagram calls out for SJ6392. Did I get an amp whith wrong transistors? BTW, all transistors are bad, I replaced them and they went bad again, need to do more thorough testing.

[The Dude]

The SJ-6392/MJ15003 is a 140V 20A device. Your 2N5633 is an 80V 10A device, so they are not rated nearly as high. I would replace with the correct parts or a better cross. That said, there may be other causes of the failure. You should start a new thread for your unit as this one is 7 years old.