Well since I can't narrow the problem down it looks like I'll get a new power supply and tube. I need my machine running Yesterday, can't even get communication from the folks who I bought it from (2 year warranty, only had it 6 months).... I've tried everything that was suggested here. So my question is, just how much do I have to worry about the red power cable, I see so much online about...don't touch it. If it's been shut down for days will the capacitors still hold a dangerous charge. (50 watt Chinese laser)... When I worked on TV's 35 years ago I just jumped everything to ground. Do I need to worry about this? Also any tips and tricks about installing. Does that huge ceramic resistor or whatever it is in power line open up, or is it solid?..... And just in case anyone has any other ideas here is my scenario. 50 watt Chinese laser, working fine one minute, the next no power to tube. Everything else works fine. Bypasses the flow switch with no change, disconnected line into power supply and hit test....nothing. No noise came from tube b4 it quit firing, no visible problems with tube or anything else for that matter, I tightened all connections, fuse in power supply is OK, The only online instructions for testing the power supply make no sense so if anyone has a suggestion about that, I'm listening eagerly. HELP.... Gotta get this thing working.