Hello, i have i power supply of Siemens in one olde machine, and i
have to repair it, but i don't know how.

the essencial, the 1 step is transform 220 VAC to 315VDC and then a
MOSFET will pulse the 300VDC at 50KHz to a transformer that out 5V at
secudary, the problem is that tranformer giver out 8V and don't
work..


Anyone can tell me if i change the frequency,. the output volt will
decrease?


Thanks.