Peavey xr600B

[Deenahrae]

I just got a xr600B not working,well sorta. Would like to repair this unit but not sure where to start. Not much of a story about it, and I don’t know the history of the previous owner.
when I got it the fuse cap was missing(replaced) the ground pin was pulled out of the plug(yikes) and there appears to be some type of dried liquid residue on one of the power transistors and a bit on the side of the big blue caps. I cleaned it up the best I know how.

the symptom is when I applied power the power and compression led light solid and then it pops the fuse. The transformer is a bit noisy too, but it is 42 years old.
Any suggestions on where to start? I would like to avoid taking it to the shop for repair if possible, but have allotted $100 for repair costs.
my knowledge is limited with electronics so keep that in mind

[glebert]

Hi! Welcome to MEF!

First thing I would say is do not hook a speaker up to this until it is closer to working. Also, do a few minutes research on safety with regard to electronics repair. No sense killing yourself on any amp. Since it is popping fuses you have something that is drawing too much current. Often that will be the power transistors. With amp unplugged (and check there is no DC voltage on big caps or transistor legs), check the transistors with the meter to see if any of them are shorted out (reads close to 0 volts with multimeter in diode test mode). Test all the legs of the transistors relative to each other, then flip the test leads around and test again (this reverses the polarity of the test).

You may want to build yourself a light bulb limiter to help with testing. It will keep it from popping fuses and prevent further damage to the amp as you work on it. If you google it you will find instructions on how to build one for $10 or so out of common parts.


Do you have a schematic that corresponds to your amp? Post it here if you do.

[Deenahrae]

Thanks for the information. I don’t have the schematic but I emailed peavey, not sure if they will respond. I have schematic but not sure if this is correct

[DrGonz78]

I have seen that schematic online at a couple of sites. There is one right here on MEF... It's the schematic posted on the thread below first posting.

https://music-electronics-forum.com/...xr600b-repairs

[Deenahrae]

Thanks for that information. So I removed all transistors and tested them. Out of 8 I have 2 bad and a very questionable one. I was looking for replacements but the only place that has something good is mouser, and those are the mj15003 for $10 a piece and I would want to replace at least 4 so they are matched.
any other places or people have these for a reason price? eBay wants way to much and they are probably fake. Anyone know the difference between the mj15003 and the mj15003G.

progress

[TomCarlos]

Welcome to the Forum....

For good measure, check each of the resistors that are connected to the Emitters of your output transistors. There are six .33 ohm and two 1 ohm resistors. Also check Q2 and Q12 to make sure those are ok.

You mentioned two are bad and a questionable one? Can you tell us by Q numbers which ones we are talking about?

By the way, how are you "checking" these transistors?

[Enzo]

Mj15003 and MJ15003G are the same part. The G is for "green" meaning that is the lead-free version of the part.

[The Dude]

FWIW: Newark has them for $3.73.

https://www.newark.com/multicomp-pro...-Private-Label

[Deenahrae]

I pulled all the transistors and check them in diode mode. I wrote down the numbers and looked at what ones are close or within 10%. Tomorrow I’m taking the board into my amp tech I use for my bass equipment. He said he would check and verify for free.
I also pulled out the cement ones(sorry I forgot what you guys call them) and at least 3 of them are way out of range and I have one that is cracked. The diodes I pulled too and one is dead. The components next to them seem fine but again this board is going in tomorrow to get checked as I’m finding to much wrong and I need to be sure I’m doing this correct. I’m kinda flying in the dark and the schematic I have the writing is not legible. Peavey emailed me asking for the serial number so I’m waiting for there reply.

the amp tech said he has new transistors @$10 a piece. He cross reference the part number(after I asked about the mj15003’s and has ones with the numbers 484140…not sure what those are.
anyway, progress but there is a lot wrong with this unit. I thoroughly cleaned the board so at least the spilled drink mess is gone.

[Enzo]

70484140 is a Peavey house part number for the transistors we are discussing.

[Deenahrae]

Thanks for clarifying Enzo.

[glebert]

If you are replacing output transistors it is often a good idea to replace the driver transistors as well. Those are the medium size ones that feed the power transistor. Sometimes the problem is that one of those will go and send an output transistor into full current conduction until it blows too.

[TomCarlos]

Here is the schematic in pdf: XR600B_Schematic.pdf

[Deenahrae]

Just leaving the tech’s now, he checked over the output board and the only thing blown is 4 transistors. I’m kinda amazed it he checked everything 4 times.
im going to reassemble shortly. I also had him chec the power board and all is good there. Once I get it all together I’ll make the lightbulb thing(he showed me how) and I guess it will be the magical moment. Does it smoke or fire up… I think I’m going to put a 2 amp fuse in in replace of the 8 amp for safety reasons.
if it does power up then I’m told to check for DC on the output. I’ll have to figure that out. I’m excited to see it come alive once again. If all goes well I’ll connect speakers and let it rip. Wish the xr600 luck

total cost at the moment $42

[TomCarlos]

Edited:

Let's start with ...

Replace t the AC Power Cord and make sure you properly ground the amp.

Which transistors are blown?

And when you plan to apply power once again, do you intend on having replacement transistors installed? And what about the emitter resistors you said are out of spec?

As a tip, it is recommended to not mix and match the output transistors. They should be of the same type.