atx psu operation

First of all, what brand is your power supply? Some power supplies are not worth fixing at all includes (but not limited to) anything named after animal like Deer, those that comes with cheap empty computer cases, and especially those made about 4-5 years ago.

Some decent power supply uses feedback to monitor volt and current useage. If there's no load or a short somewhere, it may simply shut down. Also 5v_good line may need to be dealt with to get the power supply to behave properly.

If you still can't get the psu to power up even on a known good board, you may have a problem with the psu itself. The most likely cause is a blown fuse. Although the power_on line (green line) is on secondary side, it controls the oscilator on the primary side (usually through opto-isolator for protection) and without oscilation, there is no power at all. The specific design will vary by manufactors. You will need to understand how switching power supply works as they are rather tricky to troubleshoot and repair.

--
When you hear the toilet flush, and hear the words "uh oh", it's already
too late.    - by anonymous Mother in Austin, TX
To reply, replace digi.mon with phreaker.net

thank you for your response. i was enlightened.

Ian, Look at the web page at

It has a schematic and theory of a typical ATX power supply. Keep in mind that this is just one example of a design.. the unit that you have may be similar of very different.

Above all, when you start poking around inside the power supply, be very careful. Lethat voltages are present inside the unit, and will maim or kill you if you aren't careful.

Cheers!!!

--
Dave M
MasonDG44 at comcast dot net  (Just subsitute the appropriate characters in 
the address)

Never take a laxative and a sleeping pill at the same time!!

I would suggest that unless you are very experienced in repairing mains powered equipment that you would be much safer picking one up from computers thrown in the tip - very easy to electrocute yourself poking around one of these

David - who shudders at the thought of beg> greetings!!!

Either I'v been lucky or I was doing something right. I've taken apart a number of power supplies (both ATX and older AT) and never had a shock. OTOH I've been shocked a few times when i tried to service a

480v 3 phase motor (while it was still plugged in!) and when I touched the "bell" of a 27" CRT. I've walked away though a bit shaken but with no injuries.

--
When you hear the toilet flush, and hear the words "uh oh", it's already
too late.    - by anonymous Mother in Austin, TX
To reply, replace digi.mon with phreaker.net