peavey xr600b buzzing

[checkedgoldtop]

I just got a peavey xr600b today and it buzzes much like a shorted guitar cable sounds. The mixer section works fine when ran into an amplifier through the front but when I plug a speaker into the speaker jack it buzzes at the same volume regardless of volume settings and the compression light stays on. I tried different cables and different speakers. Fuse is correct and good. Any help appreciated.

[Enzo]

Is there DC voltage across the speaker output? A simple method is to plug a cord into the amp output jack, and measure for voltage at the other end of the cord.


Most likely either the output section is blown putting DC on the speaker - loud hum. Or you have lost one of your main filter caps - loud hum.

[checkedgoldtop]

Thanks Enzo, how do I set up my meter? I am not too savvy, I got ac and dc but the sky could be brown for all I know.

[Enzo]

You are looking for DC voltage - and hoping to find none.

[checkedgoldtop]

I set the meter at 1000 DCV and got fluctuation between -.4 and 38. I also set to 200 ACV and got fluctuation between 41 and 98.

[Enzo]

Looks like you might not be getting good contact between your meter probe tips and the test points you are using.

If you are getting 38VDC on the output, then something serious is wrong in there. If you are really mnot getting DC but lots of AC, then I would be looking at either a bad main filter cap or broken solder to one of the main filter caps.

[checkedgoldtop]

Would a transformer swap be a possible place to start? Then caps? Money pit? I tried a different cable, tried unscrewing the end and going directly to the cable wire, pushed hard, still fluctuation.

[Enzo]

Transformers are the LEAST likely thing to fail in an amp, yet everyone puts them at the top of the list.

I would measure DC voltage right at the main caps and see if that is stable. And I realize I am probably leaving you behind here, but I would get out my scope and see what was going on in the circuit.

[checkedgoldtop]

I tested at the 2 capacitors (long d battery sized metal tubes?) and got fluctuation from one but not the other.

[Enzo]

The whole purpose of those two large filter caps is to provide smooth even DC power. ANy one that doesn;t is suspect.

[checkedgoldtop]

Where do I find those? I have been searching but no luck.

[Enzo]

You can always order Peavey parts right from PV.

If you are looking for 5000uf 55v caps, you won;t find them. They were a custom part and not standard value. You can find plenty of the 4700uf 63v caps as standard values. That is what PV sends out in their place. You may have to carefully drill a hole or two for the leads of the new cap to fit ionto the board. If your caps are mounted by themselves in the cabinet, then the leads don;t matter.

[checkedgoldtop]

I really appreciate all of your help so far I am getting an education for sure. Do I have to change both caps, or just the suspect one?

[Enzo]

I myself would replace the bad one to see if it solved my problem. I would then go back and replace the other one if I felt the amp needed fresh parts. My personal philosophy is to finish the repairs before doing any mods or upgrades.

[epping16]

I have the exact same problem with this amp I am trying to fix, it has a loud buzzing sound.
I checked the two large capacitors and from one I have 114V AC and 52V DC, the other has 38V AC and 16.5V DC Are these suspect faulty? Should they only have AC or DC and if so at what voltage, thanks.