HP Z840 workstation power supply clicking noise

[NConstantinou]

No power
i have the above ps which i change the TOP258eg ic.
Now i have power but is clicking and voltages are flutuating. I change all capacitors, i test all mosfets and all are ok.
i am wondering what is the value of R901! I am getting 0.5Ohms. Is that correct!
the colours look like R,R,W or silver,G Bl.

Thanks

[NConstantinou]

Can i substitute TOP258EG with 258YN IC!
Pls advice!
Thanks

[NConstantinou]

Changing the top258eg ic the ps is clicking and output voltages fluctuate.
on the ps there are 5 optocouplers and one is connected to ground with main capacitors. I am assuming that is the one for feedback.
I have checked all mosfet and capacitors non of them seem to be short.
can someone help!

[NConstantinou]

Now i got the board not clicking but 5v is fluctuating a little.
i remove the Schottky. diode STPS30L60CT and between anode and cathode i get 0.121v. is this reading too low!


thanks

[NConstantinou]

i did one test. i took 9v battery and i connected black lead to - on battery and + from battery to Anode of schottky and i measured cathode.
the voltage was fluctuating a little as it was on board.
that means is defective!

Thanks