Can a bad power supply damage a motherboard or a components attached to the mobo? I am building my first system. I know I can test the psu by just plugging it in and trying to start the system and I can check the voltages in bios (or figure out how to do it with a multimeter). But I have seen posts that say if there is a problem with the PSU then it could fry the mobo and processor. Is this correct? How would I test the psu without putting my expensive new system at risk?

PS: I know you can short the power_on green pin to a ground with a paper clip. But, I read that it can damage the PSU and gives inaccurate results anyway becase the PSU is not under load. So please dont post advising this solution. I won't do it.

Without special test equipment, the paperclip trick is all you can do, & all that really does is give you a method to switch on the PSU without it being connected to the board. Then you just stick the black probe from your multi-meter to any black wire & use the red probe to check voltage at all the various wires. Unless one of them is way outta spec, this will tell you very little about the condition of the PSU

Hellz Yea!

Check Ebay for a PSU Tester
Tester

The PS will not start up fully - and the fan will not spin - without a load on it, in fact it probably won't start up at all!
If you get any voltages at all using that method, there will not be voltages on all the wires!

It must detect feedback voltages from certain wires on the mboard connected to the main connector, the PS must be connected to the mboard, in order for it to start up fully, and the fan spin. If there is something seriously wrong with your mboard, it will not start up fully.

Try it on another working computer. If it doesn't work, it's dead for sure.
If the PS stinks of burnt wires / burnt plastic when you sniff it near it's fan outlet when it's off, it's probably dead. If in addition the fan will not turn, it's 90% sure it's dead. The fan should turn in jumps when it's off, that's normal, but it should not be difficult to turn.

If you have just added ram you haven't used in this mboard before, using incompatible ram can cause your mboard to NOT BOOT!
If you have just flashed your bios, and you used thev wrong update, or something went wrong with the flash, or the flash chip physically failed while flashing (which is COMMON), your mboard WILL NOT BOOT.

thank you for the replies. I will buy a tester. Tubesandwires - I am more worried about what could happen to my mobo or other equipment attahed to the psu if my new psu arriving this week has problems. So I want to test it before I hook it up. For 10$ I can get a tester and not have to worry about sparks and explosions. The problem is if the Antec fries everything I can get a refund for the psu but I doubt I can get a refund for the mobo/cpu/graphics card whic are like 600$ more.

My cpu and PSU will be here hopefully on wed via UPS. I cant wait to build my first system. I will probably be back with a million more questions.

AMD 3700+
coolermaster centurion
550W antec (36A on +12v)
eVga 7800gt
evga sli board

The problem isn't the new supply, which will almost always work fine when you first get it, it's what damage the old PS might have already done, which unfortunately is random.
Examples I have seen:

- in about 4 cases replacing the PS was all that had to be done - nothing else was damaged - 3 of them were sudden failures.

Most of the time a PS fails slowly - in that case it is more likely to cause damage.
- in four cases it killed the floppy drive - the led came on normally but it could not find the disks anymore; in one of those cases (a dead PS fan hadn't been noticed) it also killed the CD drive (still spun but would not read), the modem was not dead but no longer worked properly, and the video card died a short time later - in all of those cases all the rest of the pieces were fine.
- in three other cases it fried the motherboard; in two of those cases the ram, any cards, were used in the next mboard and are fine, not known if the cpu was fried because I have nothing I can test it in.

In one case I replaced the PS fan and it was fine for a long time after that (it eventually died when a capacitor exploded!).

I have replaced several other PS fans that were noisy and all of those PS's have been fine.