Dell Inspiron P66F, board LA-D801P, not powering on

[bub0r]

Hi,

I have Dell Inspiron P66F with i7 and Radeon graphics with no power issue but with green light on power adapter. I bought it just for repair learning purposes some time ago knowing it is faulty and no more details.
When I press power button, fan runs for a moment (1 second?) and stops. Similarly LED on button lights up only when button is pressed.

These are my measurements on board (LA-D801P rev 1.0) with every cable detached...
Resistances to ground on coils:
PL700 -> 1.7 MOhm
PL100 -> 7 kOhm
PL101 -> 42 kOhm
PL301 -> 58 Ohm
PL501 -> 12.5 kOhm
PL601 -> 15.6 Ohm
PL603 -> 8.4 Ohm
PL605 -> 7.3 Ohm
PL200 -> 268 Ohm
PL1102 -> 12.3 Ohm
PL1103 -> 12.3 Ohm
PL1401 -> 61 Ohm

Voltages on coils and units when power adapter is plugged in:
PL700 -> 0.22V
PL100 -> 3.38V
PL101 -> 5.13V
PL301 -> 1.00V
PL501 -> 1.81V
PL601 -> 0V
PL603 -> 0V
PL605 -> 0V
PL200 -> 0V
PL1102 -> 0V
PL1103 -> 0V
PL1401 -> 0V
KBC pin 127 -> 3.13V

When I press the button:
SIO_PWRBTN is 3.3V
PL1401 goes up to 1V and then back to 0V
PL603 sometimes goes to 0.1V so only small peak hard to detect with my multimeter.
PL605 no peaks, constantly 0V
PL200 goes up to 1V and then back to 0V

When power adapter is plugged in I do not observe any signs of higher temperature on the board.
To rule out the adapter I tried to apply current from lab power supply onto +19 rail (PJP601) and pressing power button. Result is identical, only slight fan spin and that's all.

What I find unexpected and not matching measurements from other posts about LA-D801P:
When I measure voltage on gate pins of PQ718 and PQ740 (before button press) there is some voltage measurement (around 19.6V) but it instantly drops to 0V.
What I found in other posts is there should be stable 24V there, correct?

Previous owner possibly played with BIOS die but I am not sure. I attach photo of it.

Any hints on what else can I do right now to proceed with troubleshooting?

[FZG]

I don´t think the BIOS chip has been tempered with, soldering looks stock. About the gate voltages: yes, you would expect the gate pin on an n-channel mosfet to have a higher voltage (5-6V more than the supply).

[mon2]

1) review the sticky above on charger circuits by @Piernov.

2) is the power adapter the original and for this logic board?

3) a dc power supply cannot replace the original power adapter because this is a Dell. Review the power adapter connection to locate the AD_iD or similar net name. This is a single wire line used to identify the details of the power adapter using the Dallas / Maxim 1-wire communication protocol. If this line is defective (see the mosfet in the middle), same issue as yours will result. Measure the voltage to ground of this adapter voltage ID line.

4) measure the voltage to ground of each pin of the dcin mosfets. Post all measurements.