Peavey Mega Bass SS Rackmount - Low Output

[earache]

Hi Yall

Gotta Peavey Mega Bass SS rackmount head circa '91 that has way lower output than expected.

It's recent history is that, for many years it lived in a 19" rackmount road case and was schlepped around from gig to gig, working quite happily despite the fact that all of its considerable weight was supported only by the front screws, leaving a big load cantilevered in back unsupported.

One day it stopped working after having sat for a while - no output whatsoever. The front panel was a bear to remove as all of the sheet metal pems had worked loose and the front screws were stripped. So....I had to cold chisel off the screw heads to gain access to the electronics. Then I proceeded to touch all of the connections and solder joints with a hot soldering iron.

I thought I was good because I plugged it into a speaker cab and got some output. However at practice (where I could turn up the volume considerably, not like at home) it has very low volume. Not distorted at all...just low volume.

What should I look at here? There is a stack up of circuit boards that are interconnected by by connectors and cables. I had them all apart once and tried to hit every connection with the soldering iron.
What could cause low distorted output?

Thanks in advance.....earache

[52 Bill]

...Not distorted at all...just low volume.

What could cause low distorted output?

Which is it?

Have you tried cleaning the break jacks? How about taking the preamp signal out to another amp or inputting a signal directly to the power amp?

[earache]

Which is it?

Have you tried cleaning the break jacks? How about taking the preamp signal out to another amp or inputting a signal directly to the power amp?

Woops it should read, "low UNDISTORTED output"...my bad

[earache]

So I found what the problem was with this amp. The large blue device in the attached picture, marked "U6" on the schematic, had bad solder joints which began to make lots of loud pops and subsequent volume drops whenever the circuit boards or the front of the amp was tapped/touched.



The top of this device is very close to the front metal panel of the amp...and the lip of the metal chassis lid comes very close to it also. Too much rough handling of this relatively heavy amp must have caused the solder joint to crack. A touch up with the soldering iron took care of the problem.

Thanks for your help and interest everyone!

[J M Fahey]

You were lucky that it was just a soldering problem.

That mystery part if of course unobtanium, unless Peavey happens to have a few left for servicing.

[The Dude]

Just an observation: The large electrolytic directly behind U6 looks bulged. It could simply be the plastic cover on top and not a problem at all. Or the top could be split. Or the picture could be deceptive because of the reflection. If you have any filtering or hum problems, give that a closer inspection.

[earache]

Good eyes on you Dude...but it is just as you thought it might be, which is the reflection off of the top cover plastic on the capacitor, which appear fine and not bulged.