View Full Version : Power supply troubleshooting - hissing noise.

Rich Harman
07-28-2017, 12:40 AM
My laser developed a problem today. It still makes full power but only after about 1/2 second during which time a hissing noise is heard from the power supply, during this half second the ammeter reads only about 10 to 15 mA and the laser output is low. After this half second of hissing has passed it goes quiet and the tube fires normally. This happens almost every time the tube is fired. Occasionally the tube will fire with full power immediately but not often.

There is no arcing anywhere that I can see. I had the machine opened up and the room dark, peered everywhere I could but there is no arcing to be found. The hissing noise is definitely coming from within the power supply.

I took the cover off the power supply to search for an obvious problem. All I found was the HV line laying next to a large capacitor and some marks that may indicate it had been arcing to it. I put silicone tubing over the HV line and tried again - same result as before.

It looks like I will be swapping back to one of my 80W tubes. I don't have a spare power supply for the larger tube.

I would appreciate any advice on how to troubleshoot my power supply.

Dave Sheldrake
07-28-2017, 2:31 AM
Flyback transformer is dying Rich, the hiss is internal arcing between the windings

Matt McCoy
07-28-2017, 10:19 AM
Is the capacitor bulging?

Rich Harman
07-28-2017, 6:09 PM
Capacitors looked fine, no swelling at all.