This is a thread I borrowed off a mailing list for the Roland GP-100. The GP-100 is one of the first digital amp modeling effects units. I have two of them, and was getting an annoying hum in one of them, so I spent some time this evening taking the "Broken" unit apart.

This thread is from the Roland GP-100 mailing list dated March 2003 between Rex and Kevin. I have no idea who Rex and/or Kevin are. The pictures are Kevin's, though.

Who knows but I'm glad I had it tonight.

Rex Started:

Did you ever wrestle with a GP-100 that had a jittery PARAMETER or NUMBER/VALUE knob? You know -- where you turn the knob in one direction and the display jumps two or three steps in the other direction? It's the most annoying "feature" of many Geeps, and those who must live with it curse it loudly. If this sounds like you, relax...your problems are solved. Most likely, the culprit is the knob itself. I've experienced this problem on both of my Geeps, and in each case, the problem was a small crack in the core of the knob (the central part that grips the encoder shaft). This flaw is hidden from view unless you remove the knob and look at its backside. There is one fairly wide, very uniform split that's supposed to be there. If you find two cracks or splits, that's one too many. The split causes slop in the knob-to-shaft coupling, which causes switch bounce, which causes...well, you know the rest. So do yourself a favor: go to the and get Roland's US tech support number (unless you live outside the USA, in which case you can go to and find the number that's closest to you). Then call that number and order up a couple of new knobs at US$ 2.00 each. Then install the knobs, sit back, and enjoy Geeping as it was meant to be. That's what I did, and now my Geep never jitters at all.

Rex //Computer Guide

At this point, I have no idea if those knobs are still available. My unit was in fact having the jitters. I took it apart to try to diagnose a huge humming noise making it unusable, but while I had it opened I went ahead and took a look at the jitter problem.

Just a quick how-to (this may be old news, disregard if it is and a couple pics of how to fix the encoder problem the best you can without replacing them..

Blowing air or contact cleaner will most likely make the problem worse then it is. These are not optical encoders, what happens to these usually is the grease they use to lubricate the little ratchet thingy gets all over, contact cleaner and compressed air makes it a bigger mess usually. Also what happens is the ratchet teeth get worn and it doesn't 'center' properly on the clicks. Anyhow, a phillips screwdriver, small jewelers screwdriver and a pair of needle nose pliers are all you need. I used some contact cleaner sprayed on a q-tip to clean everything, used a pencil eraser to 'burnish' the wheel and contacts, one more cleaning with the cleaner and a dab of silicone grease on the teeth - a very small dab with a toothpick.

Also, the reason I even bought a GP100 (paid 100.00 for it), is the previous owner was quoted 150.00 to replace the backup battery - its a common $3.00 CR2032 battery available at radio shack in a slip in holder as you can see by the pic. This one had the 'replace battery' screen up and the owner freaked out. If you replace it powered up you probably wont lose your presets (I don't have a schematic so I say probably), just be careful not to drop the battery on the main PCB or on the 110v mains wires/terminals that are exposed on the PS board - or you could just back up your presets on a computer and change it with it unplugged/power off I guess. Be careful when working with this plugged in, the AC wires are exposed and easy to lay your arm on by accident - trust me on that

This is probably old news but I was bored tonight and got sick of the 'jitters.' Back to the way it should be now, took ~15 minutes to do.. If you want these pics for a web page or whatever grab them now - they wont be up for long..


Thanks Kevin, I did snag those photos and have reposted them here, 6 years later give or take a few days. Unlike Kevin's prowess, it took me about 2 hours to get the GP open; and then additional time to figure out how to get the knobs off and stuff. Before searching out the original e-mail; I used quite a bit of compressed air blowing. But, nevertheless that seems to have fixed my problem; at least for the moment. My hum went away once I had the whole thing apart; no idea why. It stayed away while when I got the thing back apart.