I have an old Phase 90 that I need to get repaired. I know...well...pretty much nothing about repairing effects. I'd prefer not to send it to someone to get it fixed. I want to take the quickest, and of course the cheapeast route. I emailed MXR about it but they said they didn't repair older units.

But anyways...I'll get to the point. Right know I'm trying to figure out what is wrong with it. How would I know if the switch is bad or not? That could very well be the problem. However, it may have gotten fried on a crappy adapter. If that's the case is it fixable?

When I plug it in, my signal is fine when it is bypassed. When I engage the switch the LED doesn't turn on and there is no sound. Also the battery tends to get hot when I put a cord in the input. I've been told that that may be a sign of a bad switch. So if anybody could help me out here, I'd greatly appreciate it.

If the battery is getting hot, that's a pretty good sign that there is a short somewhere between the power supply (battery) and ground.
It's doubtful that the switch has anything to do with it.

It sounds as though there has been a poor power supply plugged in at some time. I see this problem often (hot battery) and I'll bet that it is the zener diode in the power supply that is shorted. If you're handy with a soldering iron and want to fix it, I'd be glad to send a Jpeg of the culprit...