hi!
Got fuj. siemens esprimo c5910 with power issue : no reaction to switch.

To make pc start, need to power up PSU alone without load (by grounding pson) before connecting it to mobo.

All PSU voltages are checked ok without load (stby voltage=+5v), but when connected to mobo, stby voltage becomes low : 1.8V.

Steps taken : swapped PSU with a good working one, pc starts normally.

Concluded that PSU is culprit, and particularly stby rail.

Opened PSU case, all caps are looking fine.

Any idea as what are the main stby rail check points and where to dig further to solve this issue ?

Thank you

That kind of problem used to be, a small electrolytic capacitor, and it is located in the primary side of power supply. (± 100uF/25v.)

Usually looks healthy, but...

In the primary section, besides the big cap, there is only one electrolytic cap of 10uf/25V.

It is very difficult to work without the schematic.

It seems to me that there are some more electrolytic capacitors at the primary side, but photos are not close enough to see it.

Did you change that 10uF/25v. capacitor?