We had some exciting fireworks at our annual SOARA Field Day this year! One of our generators had a failed regulation circuit and presented 160 VAC at the output. The victim of the high voltage spike was Dana, K6NR’s Powerwerx SS-30DV switching power supply.
Powerwerx does not repair them or provide schematics, but they do offer a trade-in for a discounted price with a 3-year warranty. Their warranty would obviously not cover generator abuse!
I decided to repair the power supply myself. Upon opening the case, you could clearly see the witness marks from the damaged parts. It was clear that the first section bridge rectifier had blown up. One zinc oxide varisistor (essentially a MOV) was clearly obliterated and the other one was found to be defective once I removed the protective heat shrink tubing. MOVs are designed to provide a low resistance short-circuit when their voltage rating is exceeded.
After using some rubbing alcohol on the fried MOV I was able to determine that the part number was “07D201K” – A 200V 10% 250pF MOV. I removed one of the two 300V electrolytic capacitors to gain access to the blown rectifier and MOV. While I had it out, I tested it with my component tester and found the ESR readings to be within spec. The blown bridge rectifier was part #GBU-1006. I did not have either of these parts, so I ordered them and a few spares from Mouser.
Mouser delivered the parts in a couple of days. I covered the MOVs with heat shrink like the original parts to prevent them making a mess if they ever receive an over-voltage again and then reinstalled them. After reinstalling the bridge rectifier, reusing the ferite beads from the blown part, I carefully reassembled the supply.
It powered up fine and the output voltage was 14.1 Volts as it should be. To put some load on the supply, I attached an Icom mobile transceiver and it handled that load just fine.
The total cost of the repair was $9.20 in parts, $8 for shipping, and about an hours time.
Leave a Reply