Dell Optiplex 745 won't turn on

[kamel]

Got for repair Dell Optiplex 745 almost dead, only led on mobo lights.

SIO : SCH5504-NS - Datasheet seems not to be available on the net.

Voltages measured :
Fnt_panel ICH_PWRBTN : 0V instead of +3V to be released by SB
though: RSMRST =+3.2v, clock signal is ok and supply voltage =+3.3V_AUX
PWR_PS_ON (green wire)=+4.9V
+5VSB ok

Based on SCH5514-NS datasheet available, which seems to be same as SCH5504-NS,
slp_s3 (pin123) and slp_s4 (pin124) measured +3.2V, when only PSU is plugged. It should be +0V, before pushing power button.

When I shunted green wire to gnd continiously, computer boots and displays.

Any help as where to dig further to fix Dell issue.
Wonder whether SB need replacement.

[stj]

Re: Dell Optiplex 745 won't turn on

chances are the power supply has blown if it uses the one with the wrong ceramic capacitor in it.

open the psu and take some foto's

[kamel]

Re: Dell Optiplex 745 won't turn on

chances are the power supply has blown if it uses the one with the wrong ceramic capacitor in it.

open the psu and take some foto's

Hi!
Power supply is working properly, because as I mentioned in my previous post, when green wire i.e PWR_PS_ON pin is shunted to gnd continuously, computer boots and displays.

[stj]

Re: Dell Optiplex 745 won't turn on

have you tried a different supply?
it could be poor 5v standby or a bad power-good signal.

[kamel]

Re: Dell Optiplex 745 won't turn on

have you tried a different supply?
it could be poor 5v standby or a bad power-good signal.

The PSU I'm using is tested ok with other dell working motherbords.