GK MB500 Problem FIXED !!!!!

Discussion in 'Amps and Cabs [BG]' started by Duncantein, Jun 14, 2019.

  1. Duncantein

    Duncantein Supporting Member

    Aug 28, 2011
    If you've ever had that annoying problem of your GK MB500 losing that brilliant sound that becomes scratchy, hissy, dull, crashy, etc. then this might be the fix for you.

    Disclaimer: My best advice to you is NOT to try this. Get it taken care of the right way by the manufacturer or a certified / licensed technician.

    However... If this works for you... GOOD. If it doesn't, go and BUY ANOTHER GK MB500. Gallien Krueger products or nothing!!!

    Watch the vid... before and after.
  2. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Nice for the disclaimer but this is a good way to ruin an otherwise easily repaired amp. Especially if that's WD-40 in the can.

    Spraying anything over the high voltage section introduces conductive debris attracting residue which can result in catastrophic failure down the road.

    This is something every qualified service tech should cringe at.
    Last edited: Jun 14, 2019
    BassmanPaul likes this.
  3. Duncantein

    Duncantein Supporting Member

    Aug 28, 2011
    I agree with you wholeheartedly, but promise to report how things have held up over the next 12 months. I was so frustrated with my GK MB500 for years, I tried to fix it myself and was willing to take the risk of breaking it. If I couldn't fix it, my next purchase would have been a Mesa D 800+. This looks likes a solid piece of equipment you guys at Mesa are building. Definitely will give it a try one day. Thanks.
    agedhorse likes this.
  4. Wolf


    Jan 30, 2004
    This works! Thank you thank you thank you thank you! My hero!

    I got this amp new in the beginning of 2018, and it started failing on me about a year and a half later. Sound would cut off completely within about 10 minutes of turning on the amp. Took it back to the dealer. They were merciful and didn't charge me for the fix, seeing as how it was very close to the warranty period. Said it was dirty contacts and that they cleaned it up. About 20 minutes into the next gig the sound dropped and became muffled and fuzzy (guess I got the fix I paid for). Turning the gain up and smacking the strings would eventually make it POP back to life, only for the problem to return after another few minutes.

    Needless to say I couldn't gig with it like that. For the past year and a half I've been playing direct or borrowing a friend's Markbass head. Now, after Duncantein's fix, I left it running for two and a half hours, occasionally noodling, and the problem's gone.

    These heads sound great, so it's a real shame about the reliability. I've seen a bunch of posts here about this problem. I think I know what caused it in my case: I'd use a hand-cart to drive my cab to gigs, and I'd put the head in small laptop case on top of it, and then use a ratchet strap to secure both of them to the cart's base. I think the strap pushing against the top of the head's chassis may have caused the PCB to flex, and combined with the holes in the roads and sidewalks it must've bumped some of the plastic connectors ever so slightly out of their sockets.

    Still, if I could fix it in under 10 minutes with pliers and a few drops of deoxit, there must be some way to make these connections more sturdy in production. Wonder if the new Legacy heads are also prone to this.

    Anyway, so very glad this is fixed. Will definitely be more gentle with it from now on.
    And don't try this at home. It will kill you.
  5. Bob McAlister

    Bob McAlister 6tzguy Supporting Member

    Aug 22, 2004
    Orange County, Ca.
    So glad that worked for you! I hope your wife didn’t see you doing all that on a glossy cabinet with no towel or something. I’m glad her crystal sugar bowls ok too! Gee wait! Now I’m sounding like a wife!
  6. DWBass

    DWBass The Funkfather

    I had an issue with my MB200 cutting out and the volume dropping. I put it to the side for a few months and just used my other amps. Decided to open it up and clean it with canned air. Found the label from the underside of the top had come loose and was floating around inside possibly touching stuff. Put everything back together and so far, the amp has been working fine.
    Al Kraft likes this.