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Gallien-Krueger MB500 is dying?

Evanforbass

Evanforbass

Feb 3, 2016
558
1,213
38
Denver, CO
#1
I got a used MB500, and it has been working well. At the gig tonight, the signal starting sputtering in and out, half the time not present at all, then fading in very broken/weak, distorted and quiet.

Anyone experience this? Repair ideas? Or repair cost guess?
 
#3
Evanforbass said:
I got a used MB500, and it has been working well. At the gig tonight, the signal starting sputtering in and out, half the time not present at all, then fading in very broken/weak, distorted and quiet.

Anyone experience this? Repair ideas? Or repair cost guess?
Click to expand...
Try connecting Effects Send to Effects Return with a standard shielded cable. If it works, see here for an explanation.

EDIT: Sorry, Jim... didn't see your post.
 
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#5
Try cleaning it with canned air. I had a similar issue with my MB200. Opened it up and found the label that was affixed under the lid came loose and was floating around the cavity possibly touching things. I removed it and then used canned air to blow out any dust and debris that may be touching and or affecting components. The amp has been working flawlessly for the last few years.
 
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#7
This is my collection of GK amps over the years. I feel qualified to speak on this issue. My biggest problem with their equipment are dirty pots, which are very difficult to clean properly, if at all. This will absolutely affect all aspects of performance. The other thing that happens is that small jumpers inside the electronics become loose and not well connected. I’ve had component failures as well. I am well trained in electronics, but the surface mount technology is difficult or impossible to work on. GK will fix it for, in my opinion, a reasonable price, compared to replacing it with something small and light.
IMG_1256.jpeg
 
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#9
Not to change the subject exactly, but I used my Ampeg shown in the photo for many years. Was very reliable. I bought a Walter Woods 100 watt head in the mid 1980’s, which worked ok until it just died on a mall gig. I sent it back to Walter, who said he’d never seen this problem before. I told him to just keep it. I then stayed with GK and Polytone, and bought a high powered Carvin amp as well. My advice is to always carry a backup amp. I carry a spare GK speaker cabinet as well, since I play low volume jazz and Latin gigs.
 

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#10
I'm a GK loyalist too, but I admit that I've replaced scratchy pots. The ones in the newer amps aren't clean-able. Fortunately I'm a good tech, because this is beyond what I'd feel comfortable calling a DIY-able repair.

It's not a big enough deal for me to give up on the amps, but if I did, I'd probably be thinking of something designed by a fellow TB'er. ;)
 
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#14
bass player 53 said:
GK will fix it for, in my opinion, a reasonable price,
View attachment 7307203
Click to expand...


GK MB series of heads fan-boy here also!

FYI: Due to parts availability. GK is only making available factory service/repairs for their Legacy and Fusion S series of heads.

MB, RB and older GK amps no longer have factory repairs available, you'll have to find a qualified service tech for service.

20250413_121341.jpg
 
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#15
JimChjones said:
To be the first to state the bleedin' obvious, before you get into anything more sophisticated try different leads and put a jumper cable across the send/return loop. See if its misbehaving with headphones too.
Click to expand...
I used to have an 800RB and currently have an MB500. Love the sound on both of them but had the same effects send/return problem as has been alluded to at various points in this thread. Being a lifetime achievement award cheapskate, I went with the jumper cable solution on both of them and they worked fine after that. Judging from what I'm hearing here plus my own experiences, this has been an ongoing problem with GK bass heads. I find it very surprising that GK never addressed it.

As long as we're discussing this effects send/return flaw in GK bass heads I thought I'd mention this ... I used to play with a drummer who worked for Drums Unlimited which was (and maybe still is) the premier backline provider in the MD/DC/VA area. I went to their warehouse with him one time and they had quite a few of each of the popular bass heads at the time (the mid-90's). I asked him what was the most requested bass head and he said GK 800RB - by far so I guess that besides the effects send/return thing they are probably real battle-axes overall. I've played quite a few shows with the backline provided and besides a few SVT w/8x10 rigs (always a treat), the GK 800RB w/Hartke 4x10 was very often what was provided.
 
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#18
Bob Coldwell said:
I had a similar problem with my 10 year old MB500. I thought for sure that it was an effect loop issue. But I called GK support, who said it was probably the wiring harness.

Anyway, I ended up sending it to GK for a flat rate repair, and got it back in two weeks. GK customer support is top notch, in my opinion.
Click to expand...
Speaking of harness, here are 2 partial gut shots of an old China-made MB200. I use it mostly as an ICEpower test bed now. First image, note the strain on the cable I marked with a yellow dot. Second image, look for my yellow dot again and note how the strain prevents one end of the connector from fully seating. This sort of thing may be why production was moved back to the USA -- excessively long supply chain. Couple thousand of these in the pipeline at any given time and it's a bit late (and expensive) to fix the production line. I congratulate the company for doing the right thing and pulling production back "home".

harness1-marked.jpg


harness1a-marked.jpg
 
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#19
Evanforbass said:
Can I ask what the repair rate was?
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It was $150 plus parts and shipping. The amp is pretty light and small, thus not expensive to ship. I think the total bill was $208. It might have been less.

GK doesn't do repairs on all out of warranty gear, but they did mine. It could depend on how busy/backlogged they are. I don't know, but I'm very happy with the service.
 
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#20
I have had one of these forever. The power amp died in mine and I REPLACED THE ICE MODULE MYSELF! I had absolutely no idea what I was doing. I bought it off Full Compass, popped it in, connected the ribbon cables, and it's worked ever since.
I do NOT recommend doing this, however. I lucked out.

All the advice here is great.
1. Don't spray anything in it.
2. Run cables in and out of all of the jacks a few times.
3. The effects loop is usually the culprit.
 
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