dead switching power supply

I have a dead 400w switching power supply. Looking at the board, none of the electrolytic capacitors look swollen. I took off a 420v 180µf cap with a plastic top anyway just to test it, and it is open. Problem is, if I understand the construction, this is just an input filter cap. (i.e. not something that by itself could render the device dead) What is the likelihood that if I replace it, that it is the only problem on the board? (I don't want to sink too much money into this.)

Also, when it fails, what is the possibility that some sort of damage cascades to other components?

Any other common problems with these types of supplies which I can look at?

TIA Michael

Often the input filter cap is the problem. If you have a C tester, check the value measured. It will probably be low.



It sounds like that cap is a main filter cap for the DC bus, there should be more of them, all in parallel for a 400W supply. Check each of them, also look for the bridge rectifier and check that it is okay as well as any fuses. Can you post a picture of the supply please?

Tom... :)


Thanks for the info. I would have expected more large caps too. If it helps, it is a Silverstone mini-itx supply.

Let me know if you need a close-up on a subsection of the board or have any comments on the jpg.

Thanks again,

If you replace the capacitor, use a 105deg version. They last longer.


Hi, Bit small for 400w, blow the dust etc out, also check the smaller capacitors, you need to check their ESR and capacity.

Tom... :)