Peavey Blazer 158 Hums Huge!

[timothy]

I have a Peavey Blazer 158 that I got from my brother. It worked fine for a while, but one day I got a loud hum whenever I plug my guitar cord into it. The hum does not seem to be present with no guitar plugged in, just when I try to plug in a guitar. Any ideas on where I might start to try and fix this?

[crystaltech56]

It's the old trial/substitution of a know good device until you come to the bad part. No rocket science here. I'm totally unfamiliar with the amp,but..... First off, disconnect power then examine the input jack for a good soldered connection (a visual inspection, that's why I say I'm unfamiliar with the amp, the jack might not just be visible from the back , you might have to do 30 to 45 minutes of disassembly, which you'ill have to do if the jack itself or the soldered connection is damaged, in order to do the repair). The jack may have been mechanically damaged( it only takes one good pull on the cord in the wrong direction). If the input jack is good proceed to next step: find a known good guitar and cable( proved good on another amp, no noise,  no arc'n'spark ). Connect good cable and guitar prior to powering on the amp ( loud transient noise breaks trons, speakers and you ears. Set volume to one (don't go above two) and give the plug-in-the-jack the "wiggle test" . If you get noise you know you at least have to resolder the jack if not replace it. Maybe it's best not to re-assemble amp in case until this test is done. Good Luck.

[crystaltech56]

Hello, I don't see if you conducted the test for arc'n'spark at the in put jack. How did it go? If you did ,and there was no improvement with a) a new jack installed and b) by substituting a new,known good guitar and cable; then it's time to move on to deeper trouble shooting. Questions for you: Do you have a voltmeter or preferably a VOM meter, a small signal generator( 2 or 3 transistor) , some sandstone load resistors, an O'scope? Just asking, so I can more directly answer future questions. Do you have schematic, or is it available on web? Loud hum often means problem in power circuit because some one dropped it and knocked loose a capacitor from it's mount on circuit board, or broke a printed circuit run on the board and now there is no signal but the oscillating of 60 HZ power or another circuit (input volume control on tone), Let us know how it's going. Have you read my "Your Governtment Wants to Help You" post in the newcomers? section? Have you downloaded the manuals? They are free and they are very good. Let us know what equipment  you have to work with and your level of skill; it makes it easier to give appropriate answers.  Crystaltech56

[timothy]

Sorry, I haven't been on in a while. Actually, the problem lie with insufficient solder on the input jack. A nice little dab of solder, and Voila no more hum. Thanks for the input, I will be sure to backtrack thru the other posts and keep you guys in mind if I need to repair any other amp I may have lying around. Again, thanks, you guys rock!