During revive the retro computer I discovered a problem with a Chieftec power supply:
After powering it up it is emitting high frequency noise, mainboard is not starting after pushing the power button.
I connected the multimeter and measured the STB (standby) line (violet color in ATX connector) which has to be +5V. The result is around 500mV.
After searching on forums:
https://www.elektroda.pl/rtvforum/topic1259803.html
https://www.elektroda.pl/rtvforum/topic1925712.html
https://www.elektroda.pl/rtvforum/topic1098695.html
https://www.elektroda.pl/rtvforum/topic3043926.html
https://www.elektroda.pl/rtvforum/topic968105.html
https://www.elektroda.pl/rtvforum/topic860735.html
I’ve obtained information about similar problems and the schematic for this power supply:
It turn out that there is surely a problem with capacitors. I started with replacing two 3300uF/6.3V near the 3.3V line which was leaked (C13 and C15). Here are the new ones:
Next I replaced the main cause of the whole problem: 22uF/50V capacitor marked as C34. After removing, I measured the capacity and it was dropped to 18uF, which is sufficient to raise the problem. I replaced it with same capacity but 100V, and also a little higher in diameter so I have to raise it a little on the legs:
Soldering was a little problematic because it has a wire from another element in the same hole.
After all this I was trying to power it up but unfortunately nothing changed 🙁
It was still generating this noise and standby line was not +5V.
After further investigation it turns out that there is a protecting 5.6V zener diode (D14) which is the last resort for protecting the main board. I’ve unsolder one leg to check the diode for sure:
… and indeed that was a problem 🙂
I could also see a little overheat under that diode which was not visible before:
Finally I’ve replaced this zener diode with the other I have:
And finally after powering it up I can see +5V on standby line and no more noise!!! 🙂
Power supply is working properly!
Here are all elements I’ve replaced:
