listen man
carefully
if you try to measure raw voltage from it without dealing with the sense line
that most atx and also most AT types need a signal supplied
the psu will sit there and NOT supply some rails
other than this the lack of both +12v and +5v is pretty impossible
this would mean than two outputs from the switching transformer have failed
the +12v sometimes comes from a diode to220 package
the +5v also comes from a similar package
- voltage comes from 79 style regulators
however sometimes have there own transformer
also using a single fet driver stage
so you could find the main set of chopper driver fets have failed
check these for shorts Source to Drain {on beep range}
there WILL be a low resistance Gate to Drain this is normal
if you see two transformers this will be the case
also there will be some 1uf electrolytic caps can dry up
check ones near to heatsinks esp the lo value ones
most psu have .047uf electrolytic caps in the pwm stages {around the lm723 ua494 etc oscillator regulation driver chip}
i would change all the low value caps and test the fets etc as described
what to do is take a picture of it
from above a good quality one
and post it
the eagle eyes amoungst us will spot ANY problems from this
there are billions of designs ive seen atleast 200 different psu's
circuits for this
but + voltage comes from the diode packs and not regulators
it is unlikely these have failed or there would be a bad smell from it
the first thing i do is take the board out and sniff round it
if you know the smell of fried semi's youll find the problem
payes to have a good sniff around
{after you brush it out of dust and take the pcb out the case}
dont forget to use your DVM on beep range
to beep test for short caps
+ - meter probes contacts one way beeeeep the other beep
it's an 'ok' cap or cool enough
if you find a short you can track it to the exact component using the lowest resistance range {usualy 10 or 20R} look for the smallest resistace
above this is the fried part
put the negative probe to the ground of the voltage output side {any black wire}
and test backwards using the pos probe to find shorts in psu rails if any
most often if both +5 and +12 have failed
there is a sense problem
or the usual lm723 regulator chip {14pin} has failed
this wouldnt nessisary effector the - voltage as this prob isnt regulated by the 723
sometime its a lm723 sometimes a ua723 etc
there are a few varient chips used by chinese makers
try these steps
and let us know
im sorry i put you off just trying to save you some time
but if you want to learn pictures in electronics
speek louder than 1billion words of texts
Added after 11 minutes:
cyberrat said:
Oh come on guys, it's not a waste of time.
PC PSU's fail all the time & the experience gained in trying to repair or even figure out what has blown in one can be very helpful.
Other wise what happens to the PSU? it ends up being thrown away and making more landfill.
I don't know about the country that you live in but in the UK we are running out of landfill sites/places to bury our rubbish and a PC PSU will take many many years to decompose.
The repair may only cost a few pounds to replace a few transistors or may even be as simple as a bad joint which costs nothing but a bit of his time & if he "wants" to spend that time and learn more then surely it costs us nothing to help rather than be snobs & tell him not to "waste his time" and the PSU end up as waste.
dont worry by the time landfill disappears
london will be gone also
so we can use it
this isnt a problem anyway
as its made of metal you can be double shure some worker or a magnet will pluck it from the trash squash it up
and youll be driving in it next year
its the cars that are the problem
by the time the gas runs out there will be no energy to change them into something else anyway