Help about repairing pc power supply

Thread Starter

Dzoro

Joined Feb 1, 2019
184
So i got riotoro onyks750 watt psu for cheap,i pluged it and it had 5vsb and the ps-on voltage so i conected the green wire with one of the black and the psu isnt starting but you can hear that is tryng to start but it shutsdown around every 0.3 seconds so i opened the psu i pluged it in again and mesure the big caps on the input and because it has active pfc on the caps it should have around 360 to 400 volts when is on and around 320 volts when in standby but when i turn it on the pfc doesnt start and the clicking noise continues so i unpluged it and discharged the caps i removed the power mosfets.One for the pfc and two mosfets for the switching of the main transformer and one of the two mosfets of the main transformer switchnig was bad so i replaced all 3 of them with the same power mosfets i cheked the choke is good i cheked the diode for tho output its also good so i powerd it up through a 100watt lightbulb in some case it short again and the lightbulb turned on for a sec when the inrush current is charging the caps and then turned off like it shoud and when i try to start it wit a jumper wire from green to black,still the same cliking sound happend so i unpluged it and because its a high efficiency psu 80+ bronze it had synhronus rectifiers,it had 2 mosfets in series on one side of the output of the transformers they all mesured good but i still replaced them all and still the same clicking sound happens when i turn it on and one strqnge thing is that the 5vsb is not 5v its 4.2v and i dont know if that can make the thing turn on and shut down multiple times a second. I have repaired many 80+ power supplies but this one is such anoying so i had last one hope to ask here if some of you had the same problem if you know how i can fix it
Thanks
Dzoro
 

wayneh

Joined Sep 9, 2010
17,030
Have you looked for the service manual and schematic? There looks to be some on the internet but there are many "Onkyo 750" variations.
 
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