How to diagnose a power supply...

I've got a computer that recently crapped out, really old, about 5 years since anything significant's been done to it (no new hardware installed), and now the computer will go back and fourth from not turning on at all to turning on, but only with optical drives and hard drives spinning up, no video output, no bios, and the hard drive doesn't seem to do anything, so it's not being accessed, almost like the motherboard failed. However, not totally convinced that I need a new motherboard (I would much rather spend for a new PS than a new motherboard...), I've taken the power supply out, and with access to my design team's shop full of goodies, (including electronic components, soldering irons, multimeters, etc. etc.), I plugged it in and ran some simple tests on it.

-I checked for continuity between all the ground, 5v, and 12v leads, all were good on all plugs, 20-pin and otherwise.

-I checked the voltage between ground and every single lead on the 20-pin plug, without a single millivolt registering anywhere.

-Tried connecting the green wire to ground, according to literature I found online, this should turn on the supply, and it didn't. I also made sure the "sense" wires were where they needed to be, and they are properly wired in. No voltage anywhere.

I'm pretty sure this thing's busted, but I just wanted the opinions of people who know more about this than I do, is there some no-brainer that I'm missing? Thanks!

 

Log in or Sign up to hide all adverts.

This right here would have told me all I needed to know, w/o having to bust out the multi meter.
I swapped out a power supply on one of the PCs here at work last week because it was doing very similar stuff. It would boot up normally, but then would go into a 'stand by' mode. You could press the power button and the power button light would come on, but nothing would show on the monitor. The power supply fan would not come on either. I swapped the PS out and haven't had any problems with it since.

 

Log in or Sign up to hide all adverts.

Without looking at it...I'd say it's about 50/50 between motherboard and power supply. Either way it will cost you about the same. If the motherboard is that old..it's almost not worth putting any money in to it.

 

Log in or Sign up to hide all adverts.

Yeah, I'll probably borrow a friend of mine's old 300w PS and give it a go, and if that doesn't work, then this computer becomes a nice set of spare components including a mini-ATX case and two optical drives! appreciate the help

Please Register or Log in to view the hidden image!

 

Its not worth the hassle. Its more economical to buy a new one.

 

One other idea, worth trying because it's cheap. Try a new lithium battery on the motherboard. Strange things can happen if the bios memory battery goes dead or weak.