grayn Posted November 7, 2022 Share Posted November 7, 2022 I've owned and used this MB500 for around 3 years. It's been great until recently. When I switch it on, it starts off very loud, far too loud for the settings. Then after approx 5 mins it settles down to normal. It stays OK unless I re-plug my bass back in, when the problem re-occurs. I have tried changing the speaker cable but no change. Any ideas what the problem may be? Cheers. Quote Link to comment Share on other sites More sharing options...
Downunderwonder Posted November 7, 2022 Share Posted November 7, 2022 I am no tech, but that sounds like a dodgy pot, either input or master vol, that is shorting. You could audition the fx send somehow and if that is blowing out at the same time then the problem is in the preamp, otherwise it's in the output section. Save your tech 10 minutes of checking time. Quote Link to comment Share on other sites More sharing options...
Davebassics Posted November 7, 2022 Share Posted November 7, 2022 When it "settles down" does it snap back to normal volume or does it fade back to normal volume gradually? Quote Link to comment Share on other sites More sharing options...
grayn Posted November 7, 2022 Author Share Posted November 7, 2022 4 hours ago, Davebassics said: When it "settles down" does it snap back to normal volume or does it fade back to normal volume gradually? It snaps back, straight to normal. Quote Link to comment Share on other sites More sharing options...
Davebassics Posted November 7, 2022 Share Posted November 7, 2022 Could be a connection problem or a bad relay. I'm no expert Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted November 7, 2022 Share Posted November 7, 2022 I would first check the ground soldered lug on the volume or gain pots. Quote Link to comment Share on other sites More sharing options...
grayn Posted November 7, 2022 Author Share Posted November 7, 2022 Thanks guys. Looks like I am going to have to find a good, local tech. Good job I kept hold of my old GK Backline 600. Quote Link to comment Share on other sites More sharing options...
grayn Posted November 8, 2022 Author Share Posted November 8, 2022 I emailed GK and they replied with this advice: "This sounds like it may be one of two things: Pots or the Wire Harnesses. I can tell you that most likely it will be the wire harnesses then the pots." Cheers. Quote Link to comment Share on other sites More sharing options...
bassbloke Posted November 8, 2022 Share Posted November 8, 2022 +1 for pots. My MB500 Fusion has this issue. No harm getting amp overhauled by a local tech for a few quid. You'd be amazed at the difference Quote Link to comment Share on other sites More sharing options...
grayn Posted November 10, 2022 Author Share Posted November 10, 2022 Amp with local tech, I hope it's back for a gig on Saturday. Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted November 10, 2022 Share Posted November 10, 2022 Let us know the results. Quote Link to comment Share on other sites More sharing options...
41Hz Posted November 10, 2022 Share Posted November 10, 2022 Sometimes you can sort out a dodgy pot by twiddling it from min to max 20-30 times, worth a try, though from your description it sounds like something else. Quote Link to comment Share on other sites More sharing options...
msb Posted November 10, 2022 Share Posted November 10, 2022 I had my MB200 develop the pink ring of doom, I looked around at other similar amps and decided there was a reason I loved that little MB200. I got the MB to a qualified repair guy , and it runs like a charm again. My problem turned out to be the fan , and when it didn’t work the power module burned out. Still , the repair was much cheaper than buying a new amp. And once again it’s a reliable little workhorse. Quote Link to comment Share on other sites More sharing options...
grayn Posted November 13, 2022 Author Share Posted November 13, 2022 I got my amp back, yesterday morning. The local tech had cleaned up the pots. Took it to a gig last night and it performed excellently. Tiny amount of cash and it's all OK. Great stuff. The band had a rehearsal the day before (Friday) and I used my GK Backline 600, which had been doing nothing for a couple of years and it worked just fine. Nice to have a backup. Cheers for everyone's advice.😀 2 Quote Link to comment Share on other sites More sharing options...
Lozz196 Posted November 13, 2022 Share Posted November 13, 2022 Nice to hear of a good ending re amp issues 1 Quote Link to comment Share on other sites More sharing options...
msb Posted November 13, 2022 Share Posted November 13, 2022 Some say that Class D amps can’t be repaired , but as long as you can find a good qualified tech you’re fine. Good to hear it’s running normally and wasn’t an expensive fix. 2 Quote Link to comment Share on other sites More sharing options...
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