How do I fix my crate b80xl

There is a short somewhere, check your wiring and solder points.

1. Sounds like it's the input jack., but it could be the volume knob. Have you tried turning Gain1 and Gain 2 or the Clean Channel volume? Try them first when you're plugged in to the jack on the left , then when you're plugged in the back. If none of these work, it's most likely the preamp. 2. Even if the preamp is shot, there's a quick fix - get a guitar preamp or an effects pedal - they have volume and tone controls. 3. Finally - many pros just plug into the aux jack(on the rear panel) and control the volume and tone through their instruments. Hope one of these works. Good Luck.

That is probably a momentary switch that is dirty and sticking. These onboard effects on guitar amps are usually nothing more than a computer sound card and I've found bad connections going to and from them as well. I do think that switch is dirty and sticking, though.

I don't know how you know the tubes are good... It is possible they are microphonic... try tapping them with a pencil (only need to worry about the smaller ones).
Beyond this look for cracked circuit board or bad solder... especially near the control pot leads. This is a common problem. Look for cracks near the booard mounting points.

Download it here:

http://www.crateamps.com/pdf/manuals/BX80_OM.pdf

A possible problem MIGHT be marginal switch contacts on the external foot controller cable. If you are not using the foot pedal, these contacts must maintain contact to keep the same channel selected.

You have a broken solder joint. You'll have to disassemble the amp enough to get at the soldered side of the circuit board that the controls are mounted to and touch up any suspect solder joints. Just be sure to resolder only the joints that were originally soldered or need to be soldered. Hope this helps.

Their may be a schematic on the inside of the amp.I don't remember if Crate puts one or not. And I have had several Crate amps. never needed repair except for tube replacement. If there is not one in side , go here and find what you need . http://www.crateamps.com/support/warranty/ Good luck DFD please rate me TK U

If you can solder, try resoldering any connections on the board that appear grainy or have rings. It is likely that after the unit has been working for a while, the heat is causing a marginal connection to open up.

Keep us posted.

Dan