Fault Finding A Dead PSU

[HalfManHalfSaab]

Hello All,

I have a dead power supply from a Netgear 24port switch. I can see a few people suggesting they have replacement units however I would like to try and repair this unit if possible.

It's blowing fuses immediately, even if there is no load (so I can't measure the outputs).

My question is, what do I look for? There is no sign of anything burned out, no bulging caps or charred up resistors. Am I just going to be metering everything? Are there any tricks to isolate certain components to rule them out, or any common failures I can look for?

All help welcomed!

[tec5c]

Blowing fuses immediately is a very strong indication that there is a short on the AC side. A good place to start is by checking the bridge rectifier. If this checks fine, perhaps posting up some photos of the inside of the unit can help us aid you in what to check.

[German_EE]

1) Check the bridge rectifier

2) Check the smoothing capacitor(s)

3) There's going to be one or more large power devices (FET or transistor) on the primary side, check them.

4) Protective devices such as MOVs can sometimes fail short circuit.

[HalfManHalfSaab]

Blowing fuses immediately is a very strong indication that there is a short on the AC side. A good place to start is by checking the bridge rectifier. If this checks fine, perhaps posting up some photos of the inside of the unit can help us aid you in what to check.

Thanks, I shall give that a go and post up a link to some photos.

[HalfManHalfSaab]

1) Check the bridge rectifier

2) Check the smoothing capacitor(s)

3) There's going to be one or more large power devices (FET or transistor) on the primary side, check them.

4) Protective devices such as MOVs can sometimes fail short circuit.

I'll give these a go too - many thanks for the suggestions.

[coromonadalix]

If you check the mosfets, remove them from the board, you can get falses readings depending how the circuit is designed.