Teaching Myself How To Troubleshoot Variable DC & Arc Lamp Power Supplies


Sep 25, 2004
For the last couple of years or so, it seems as though I've been "collecting" Variable DC and Short Arc power supplies. It all started when I fried my very first, relatively new Mastec 30V/50A Variable supply. The Mastec's are not very forgiving of minor short circuits or connection arcs. I was simply touching a hot wire to an automotive style HID ballast to power it up for bench testing and she blew. Tried a second Mastec and pretty much the same thing but this time it was an unstable 25 Watt, cylindrical flashlight ballast with lamp that took it out.

I finally got smart and started to buy industrial/telecom grade Sorensen supplies made in the 1980's. The first one was a 40V/50A. It lasted me quite a while until I wanted to get one of the Sorensen 40V/70 Amp units. If 50 Amps is good, then 70 must be better. So I gave the old one to a buddy and bought the 40/70. It's only 125 lbs so I had to crane it into position on top of my tool box. She worked great until…..I was test running one of my newer ORC 500 Watt Gunfire Simulator Short arcs – not the lamp, just the cooling fan. The fan requires 200 Volt AC, 3 Phase, 400 Hz power and I had just hooked up my new VFD to power the fan. The searchlight 28 VDC system must also be powered up to close some relays. Well…..I didn't see a tiny AC short to 28VDC frame ground and my poor Sorensen gave out its' last breath.

I really liked the old, heavy Linear supplies but I was tired of lifting them around so I decided to convert to the newer, much lighter Switching Supplies. I watched Ebay for a while unit one of the Sorensen DCS40/75E's came up at a reasonable price. It was not guaranteed so I took a chance in buying it. As luck was with me, it fired right up and I still use it today. I liked it so much that I wanted to buy a non-working unit to give me some spare parts. I picked up a unit for real cheap. As soon as it arrived, I opened it up and looked around for any obvious problems. After a few minutes, I noticed that a plastic 2-pin header connector had backed off of a PC board connection because the contact pins had melted off the PC board. As a result, the main controller board was not receiving power. I hard-soldered the wires back in-place and she started up and ran just fine under nearly full load. So now I have 2 perfect 40V/75A supplies.

I had so much fun doing that, I decided to find another unit that was not working to see if I could fix it. I picked up another one very cheap. As soon as I popped the cover, two things were noticeable. An input filter capacitor had literally sheared off a PC board and was laying on the case floor and the plastic input power header that clips into the case had its' ears torn off so it was flopping. I bought identical replacement parts for less than $30.00, installed them and she fired right up and worked fine at nearly full load.

This is too much fun! Last week, I came across a 100- 300 Variable Watt Short Arc Power Supply that was "for parts". Got it to my door for $85.00. It came with a nifty little 300 Watt Short Arc Fiber Optic Illuminator attachment with a 4', very heavy duty fiber optic cable with a "pancake turner" style fiber optic diffuser at the end. It looks like you would use this for inspecting very small, dark and hard to get at areas. When I plugged it in and turned it on, the power LED lit but nothing else happened. I pulled the cover, looked around for anything obvious, but did not see anything wrong. I probed to make sure power was getting through the main switch/breaker. It was. Despite being 25 to 30 years old, all the components looked like they were only a couple years old. The ignitor is built-into the power supply but there is no separate ignitor switch. It simply ignites a few moments after the "On" switch is turned on. The switch was On and I was moving around the signaling cable (not the 40KW insulated high Voltage cable) on the back of the PS and all of a sudden, it fired up and ran perfectly! So I've spent all morning cleaning and polishing up the PS and illuminator. My intent is to find these "non workers", repair them and sell them to make a few extra dollars. But this system is such a neat little "very tight places flashlight" that I might just keep it. I really just wanted some troubleshooting experience.

I've also recently picked up a brand new and unused 350 – 1200 Watt Newport Universal Xenon and Mercury Xenon Short Arc power supply to replace my very old equal Wattage but very heavy Linear SA supply. The new one is only 20 lbs and runs off of 120V instead of 240V that the old one runs from.

I just seem to be collecting DC and Short Arc power supplies for some unknown reason. I can't seem to get rid of them.

Here's the Fiber Optic Illumination System. EDIT: I just listed this For Sale on the MarketPlace.

Can someone tell me if the tip of the wand is supposed to be smooth and polished for better light transmittal? If so, what can I use to do this work?

I just had to break out the SemiChrome Polish and polish up the nice Aluminum finned lens holder assembly.

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JP Labs

Newly Enlightened
Oct 14, 2005
Nice insight to common repairs you have managed, thanks.

I always fear that failed electronics will have dead, but visibly intact, components that I will never find. The fact that you have found, and repaired, several fairly evident mechanical failures to bring these back to life is encouraging. Good work!

Then again, you did smoke a couple, too. Win some, lose some. And you seem to be on a winning streak.