Fuse blown on HGM

[Xytrell]

I moved recently, and when I went to start up my HGM for the first time, it lit down the return bore like it does sometimes. It appears the spark gap was knocked out of whack on the trip. I adjusted it and started the laser up again. The fans turned, the cathode heated, but the LEDs on the control board didn't light, and neither did the laser. I found out later the fuse (F3 on the drive board, see below, bottom left) had blown. This hasn't happened the other few times it lit down a return bore. I've replaced the fuse, but before I try again, I wanted to be sure it wasn't indicating some other underlying problem I need to fix first. I have the schematics, but I can't really make heads or tails of them.



Thanks

[Hemlock Mike]

Xytrell --

What you show here appears to be a basic low voltage DC power supply board. The filter caps are rated at 25 VDC.
There nust be a bunch more circuitry somewhere and I'd start by looking at the circuit part powered by that blown fuse.
Sometimes, fast blow fuses just fail because they have seen too many "starts".

Mike

[mixedgas]

Xytrell --

What you show here appears to be a basic low voltage DC power supply board. The filter caps are rated at 25 VDC.
There nust be a bunch more circuitry somewhere and I'd start by looking at the circuit part powered by that blown fuse.
Sometimes, fast blow fuses just fail because they have seen too many "starts".

Mike

Thats a floating transistor driver, yes, its a unregulated DC PSU, but that little transistor in the metal can switches the bases of the pass transistors, based on the signal from a optocoupler. When that board pops, usually something in the passbank was very unhappy.

Check the passbank transistors for collector to emitter shorts or base to emitter shorts

Usually this is very obvious as they become slags of shorted metal inside.
I've pmed you with the contact info for a hgm engineer.
Steve

Steve

[Xytrell]

I contacted the guy Steve referred me to. He told me to check the zener diode on the control board as well as the heat sinked bridge rectifier on the drive board - both tested fine. I started it up just now and it fired first time! I shall have to call it Laserus... or was that Lazarus? I guess it was just a surge or a bump or something that blew the fuse. OR... or maybe it'll die again next month. Who knows . As long as it doesn't become reminiscent of Mr. Gus's fight with his HeCd.

He also recommended I eliminate the spark gap alltogether, reverse the polarity on the starter, and move the thermal interlock to the anode. Also, my 30A breaker didn't blow even at 34A tube current (for a few seconds or course).

So THANK you Steve and THANK you HGM engineer who shall remain nameless.

[mixedgas]

So THANK you Steve and THANK you HGM engineer who shall remain nameless.[/QUOTE]

Your welcome.

steve