HP nx7300 power on by itself

[DZD]

Hi everyone, I have a strange problem with an old HP nx7300. The motherboard P/N is 441094-001 (6050A2042401-MB-A02). So, when I connect the power supply the fan start rotating at 100% and nothing more. Then, if I press power button I can see power led on, the fan reduces its speed, the optical unit starts reading (without media), the LCD backlight goes on, but nothing appears nor to LCD neither to external monitor, no caps lock led blinking and no beeps. I have already re-flashed the bios chip with an external programmer but nothing has changed. No chips appear damaged, by visual inspection. Any suggestions?
Thanks in advance.

[Duranitron]

Re: HP nx7300 power on by itself

try a known good memory module.. try to measure vcc of bios chip and also the rtc battery.. try to operate with bare parts.. motherboard with external monitor

[DZD]

Re: HP nx7300 power on by itself

Hi Duranitron, and thanks for your answer. I already have tried with several memory modules (without memory the behavior is the same) and other bare parts. VCC of bios chip is 3V and the same is for the rtc battery (it's new). I think there is a diode or a little resistance broken on power-on circuit... or something like this. Reading GALLO 1.0 schematics I'm not able to rebuild the power-on sequence. Maybe you (or someone) can tell me the right tensions mosfet by mosfet. Thanks!

[Duranitron]

Re: HP nx7300 power on by itself

try to check all power rail voltage specially the ALW voltage... try to find schematics for this unit...
the voltage sequence is there on the schematics