820-3115-B Power up and down loop

[machelper]

Hi everybody ;

No corrosion and not dropped machine;

When Push power button fan spins but no sound,no screen,not light on status led and power off and start it self again, if i remove memory,machine beeps and not turn off.
Removed every cable,connectors and pull out board nothing changed.
I'm using 5A / 30V adjustable dc power supply and working with magsafe cables on boards when repairing boards. Its very helpful for describing problem. This machine starting with 0,8A and going 1,25A ( its normally of post process) PSU cuts power Constant Current LED and start boot process again.

Note: Removed LCD backlight fuse,replaced BIOS,

Sorry for bad english...

Thanks

 

[aprendiz]

Voltage on F7040 is stable??, Should be about 12.6V... Check sense resistors from ISL6259...

 

[machelper]

Yes 12.6v is stable , also removed fuse and injected 12.6 v directly nothing change