Intermittent Rhythm/Solo on Crate GLX1200H

[kms0521]

Jon, is there some way I can send you an excel file that has my measurements for A, B, B1, C and D as well as the other components you suggested I check. It doesn't format well for me and I don't have attachment permission.

Thanks,

Kurt

[g1]

The footswitch jack contains 2 'switches' that must close for the amp to work and change channels properly when NOT using the footswitch.
If we had that section of the schematic it would be a lot clearer.
If the jack contacts do not close properly when not using footswitch, the panel switch will not work. And intermittent faults can also be caused by oxidized contacts in the jack.

[Jon Snell]

Warming could be a cold joint opening up then closing when cool.

nosaj

All we are looking for is unstable changing voltages on those points, ref the truth table. They will be either 10volts or 0volts.
The little transistor is my worry; I think it was Peavey had an issue with a similar circuit and their transistor was against a resistor that was getting hot. Just an idea.
If the pedal is not connected, there are no links for dodgy contacts within sockets to worry about.

[kms0521]

One of my voltage readings, like across R67 (B1) and R32 (D) on all channels, are 16.3V. Others are only 2.8V like D25 and R74 with Channel 1? Man this tough. I'm not sure I know what I am doing, but when I do go to a repair tech, I'll at least have some good background if it saves time. Thanks Jon.

Kurt

[Enzo]

A good tech never assumes the previous tech made no mistakes. He will always start from scratch and make his own measurements. What he wants is a clear and concise description of the complaint.

regarding the footswitch jacks. The contacts may seem clean, but MEASURE them with an ohm meter. The closed contacts need to have less than half an ohm resistance. They might measure 3 or 4 ohm and work, but the fact they are not pristine - as in half an ohm - is evidence they are not right. Your problem in intermittant, so iffy contacts can well be the issue or involved at least.

[g1]

If the pedal is not connected, there are no links for dodgy contacts within sockets to worry about.

The footswitch jack is a stereo switching jack. It is not shown on the schematic.
If you look at the footswitch 'ribbon' cable (J21) shown on the schematic, it's a dead end. The front panel switches can not function without the 'switching' connections made by the jack which are not shown.

You could hardwire some connections on J21 to make the amp work without the footswitch jack.

[Enzo]

Oh sorry, I just been skimming, not really getting into this.

[g1]

There we go. J3 connects to J21 of the switching circuit.
What you can try for a test is solder a jumper from pin 1 to 2, and another jumper connecting pins 3 & 4.
Then the amp should work without the footswitch, even if the jack is bad. Now if it still does not work right, you can continue with the other troubleshooting. But at least you have eliminated the simple, common fault.

[kms0521]

Thanks all. I'll give it a shot and let you know. Decided not to get to a technician since I've already spent $80 without a diagnosis and any future diagnosis is likely to exceed the value of the head. Might look into getting a new or reputable used head. Kind of like the solid state sound (and effects) but would consider tube amp. I play a Les Paul and an early 70s SG. Any recommendations?

KMS

[TomCarlos]

KMS:

I found a video where a guy is repairing the Crate 3 Button Footswitch. Take a look - Crate Service, Repair, and Demo. Watch the first 10 minutes.