SMPS multi port power supply

[Revo2Maxx]

So had a friend reach out to me today because 2 of his power supplies were bad that he uses for his cameras. He bought a power box like I use for my Analog cameras that I call a PDU. Power Distribution Unit. I have some from 4 port to 18 port and range in 12vdc to 24vac.

So because his has gone bad twice now he asked if I would be willing to take a look at them for him and loaned him one of my 8 port units for now. After bringing them home and taking them apart for testing the first one had an issue with the main power capacitor AKA (Bulk Capacitor) and thought yeah that was easy and happened to have a replacement of the same value. I De-Soldered the bad cap and installed the new one, I then tested it and sure enough that was the problem. Put it all back together and thought for sure it was going to be the same issue for the second one. However after taking it apart and testing the CAP it was still good with a constant DC voltage as you would expect the cap to provide. So I had to do some more testing of the unit. Going down a list of things that I have ran into the past. Everything checked as ok. Then this lead me to the Feedback circuit and again all the caps tested good. So after some more probing and testing his second unit fault was with a 1k Ohm POT that is used for changing the voltage when the power supply to a device at distance drops down You can turn up the POT to give the output voltage a higher value. Like lets say when you put a 12v camera on the line that is 200 feet away and the voltage at the unit drops to 9.9v and the device works at 10.5 v to 14. You can give it that extra power it is looking for to keep going.. So removed that POT and installed a new one.

So I know that in the past I have said most times with Power supplies be it a wall wort or a PDU type that the main part is most always a Cap. I thought I would just share this in case there was someone that might have a PDU that they replaced the CAPs because they know how to solder but maybe not how to track down faults within a electronic circuit.

You know your fault might be like this if your Voltage on the PDU has an unstable power like going 8vdc to 10vdc and will not stable out anywhere in the 12v+ that it is rated for. If testing the caps and the unit has a POT normally would be next to the LED and easy to access. Then make sure to check the POT because it can be one of them parts that is easy to over look. If you remove it and test with a Meter either bad 100% or just will not adjust to 1k or whatever the POT value used for your PDU then replace the POT..

Good Luck and Be Safe.