PSU dead with purple wire working

[inspiron]

Hello

Today i got a strange problem, my pc wasn't turning up at all checked inside and i thought that problem is from PSU so i tested my system with another (same brand same 500W) psu and it turned up without any problem.

So the psu is dead, as i'm a little familiar with electronics i opened it but i didn't found any bad capacitors and not any sign of physical damage so i tried to test it with a voltmeter. the purple wire (standby one) is giving me accurate 5.03V and i even tested it under load and the voltage was still 5.03.

But when i try to start the psu it just doesn't turn up, the fan spins a little (half a second maybe) but nothing happens, i tried to start it with different loads (because i read that psus will not turn on without load) but nothing worked.

so i asked my question here to know if you have experienced same situation before and can help me to find out what is wrong with this psu (if picture helps you to help me 😀 tell and i will post some pictures from psu inside).

 

[compulsivebuilder]

Just because the 5V standby voltage is good doesn't mean that the rest is good. The standby power is generated by a separate circuit. It's completely possible that the main power supply is dead and only the standby power is working.

 

[inspiron]

i know , i was meaning that the cable, fuse and other common parts are working. now if we assume that the damage is not detectable by eye what part do you think has caused this problem ?

 

[hunter315]

http://www.youtube.com/watch?v=5FWXgQSokF4
Do the paper clip test as shown in that video, if it wont spin up the fan then its probably dead.


As said above, the 5VSB rail is a totally separate circuit inside the unit, you could fry 98% of the PSU and still be getting standby power as long as the transient filter and the simply stand by circuitry was still going.

 

[iam2thecrowe]

i know , i was meaning that the cable, fuse and other common parts are working. now if we assume that the damage is not detectable by eye what part do you think has caused this problem ?

The PSU is causing the problem. Look, unless you can spot bulging/leaking capacitors then you cant really fix it without schematics, testing equipment (oscilloscoper, load tested etc..). So just buy a new PSU.

 

[inspiron]

i have bought a new one but i will still try to fix this one in the next week and i will report the results here (i have oscilloscope , signal generator , multimeter , soldering equipments , schematics of the current PSU , and almost all parts used in this psu , ... so i will go for it).

 

[iam2thecrowe]

so you have tried the paper clip test? did it power on properly? if you can get it to at least power on you could start checking the rest of the voltages and go from there. Since your persisting to fix this, search the net, there are some tutorials about SMPS repair which i have read and they would be very helpful. They tell you components that commonly fail and things to check. hers just one of the many available http://www.electronicrepairguide.com/Smps-repair.html
google http://www.google.com.au/#hl=en&q=smps+repair&oq=smps+repair&aq=f&aqi=g1g-s6g-v3&aql=&gs_sm=e&gs_upl=54516l56110l2l56188l2l1l0l0l0l0l391l391l3-1l1l0&bav=on.2,or.r_gc.r_pw.&fp=df7165f2a5cfdae4&biw=1280&bih=843