The Story

Back in December I bought a new 24V 5A switch-mode power supply from a seller on our local Trademe auction site for NZ$45 delivered. When it arrived I tested it and nothing, no output.

The options were to send it back or fix it. The risk is that if it’s not easily repaired I may not be able to send it back under warranty. Since it was mid December and it wasn’t that expensive, I decided to have a go at fixing it.

NOTE: these power supplies contain dangerous high voltages – don’t try this at home.

Repairs

The case had a dent suggesting that maybe the courier package had been dropped or had something heavy dropped on it. The first step was to open it up, then a general inspection and panel-beat the case back into shape.

It didn’t look too bad inside. There is a fuse and mains filter, and inductive filter on the output. Construction and soldering looked pretty good.

Removing the board and a closer inspection quickly identified the fault. The output rectifier diode which was attached to the metal case for heatsinking had 3 broken solder joints.

I suspect it had been dropped, the circuit board with all the heavy components had moved but the diode attached to the case stayed put. Resulting in broken solder joints.

The repair was simple. Re-solder the diode and put it all back together.

It was now working correctly.

Conclusion

In this case the repair was simple and it saved the hassle of sending it back, saved the supplier time and effort, and got my job done before Christmas. If I had sent it back, I probably wouldn’t have received a replacement until after Christmas.