each optocoupler informs the primary voltage status of a secondary voltage. A method of repairing these sources is not connected to ac, to replace the one led by an optocoupler, applied dc voltage with a controlled source in the secondary and must turn to approach the maximum voltage of the secondary monitors.
It seems to be a SMD based Circuit . My suggestion - don't try to repair this kind of SMD based Power supply circuit . This SMD Based circuit will ***** your brain and you will not found the parts easily .
I am also looking for a diagram of Bestec power supply which is also 4 photocouplers like yours . This power supply problem is - The Power supply is OK but It is restarting at loaded condition .