Need Help! Channels Switching Automatically?

[timcanhit]

I have an interesting problem that I'm hoping someone here might know something about. I have 2 amps (a crate gxt 100 combo and a crate gx-900h head) that have started behaving very strangely. the channel selector switch on the gxt 100 doesn't function at all, but after a few minutes of playing, it will start to either: cut in and out, fade in and out, or switch between channels automatically. The gx-900h acts similarly, but when it cuts out, you can faintly still hear the guitar. They were both being used in my band in a basement, so my only guesses to go on are either dampness or the power source they were plugged into. I've since tested both at a different location, but the same problems remain. I'd just like to get an idea whether it's worth having it fixed or not, or if it'd be a generally simple fix I'd be able to do myself. Any help is much appreciated.

thanks,
tim

[Don Moose]

The thing to look at is the low-voltage supplies that run the switching circuits. Something there isn't happy - suspect bad solder joints and/or failing filter caps. I don't have ant crate shematics, so I can't be more specific.

Try a search on CRATE and CHANNEL or SWITCH and see if this problem has come up before and had a clean solution.

Hope this helps!

[Don Moose]

Another half-idea - if you're not using the footswitch jack (if any) ... or even if you are, I wonder if the contacts have gotten dirty enough to occasionally dis/connect.

If it's/they're regular 1/4" jacks, try plugging a plug in a couple of times (power off!)

[Gtr_tech]

If theres zeners that regulate the low v supply I'd start there first. They have a tendency to heat up enough to partially desolder themselves from the board. Another thing to check would be the jack that is for the footswitch.....clean the shorting contacts and verify the solder to be ok on the underside of the board.

[Enzo]

I'm with DOn and Gtr here. All those symptoms sound like jack problems to me. For some reason the Crates seem more inclined to them. The little cutout contacts on the jacks get dirty or oxidized.

The foot switch jack contacts are grounded by these contacts until you plug into the jack. If they don't come together, you get problems. Same thing with external speaker jacks and headphones jacks. The contact that cuts out the internal speaker connection fails.

I use a GC 9337 burnisher to clean them. It is 1/8 wide so it fits down inside the sections of a CLiff style jack. MCM sells them for a couple bucks. There is a wider one that is great for open frame jacks like the Switchcrafts in all the older Fenders.



Also check the solder under all the jacks as well as the controls along the panel. ANd under all the large 10 watt cement power resistors.

[timcanhit]

Thanks so much guys, I think you're onto something. I'm going to look into this when I get some time this weekend. I'll let you know how it all pans out.

cheers,
tim