Please Help. Hp 8460P Motherboard not turning on.

[wrongpolarity]

Hi All,
I have been struggling to repair a HP 8460P laptop. Motherboard does not turn on. I have traced the problem to what seems to be a missing signal KBC_PWR_ON causing Trip2 on IC 5006 (TPS51123) to be activated.

The following components have been replaced but the problem remains.
C5191
C5192
U50006

Listed below are voltages appearing on U5006 when the Motherboard is supplied with power from a bench power supply for the first 15 seconds or so.

Pin 1 (Trip1) = 0.65
Pin 6 (Trip2) = 0.65
Pin 8 (Vreg3) = 3.31
Pin 17 (Vreg5)= 5.13
+V3A (Measured at Pin 1 of L3013) 3.37
+V5CP (Measured at Pin 1 of L3012) 5.13
KBC_PWR_ON = High
Pin 23 (Pgood) = High

Current drawn at this moment 24.00mA

15 seconds later... All voltages above still present except

Pin 6 (Trip2) = 0.00
+V3A (Measured at Pin 1 of L3013) 0.00
KBC_PWR_ON = Low
Pin 23 (Pgood) = Low

Current drawn at this moment 18.00mA

Please help and advice. Thanks!

[mon2]

Review the charger IC @ U7.

Carefully measure and share the readings of voltage to ground for:

ACDET ; pin 6
REGN ; pin 16
VCC ; pin 20
ACOK ; pin 5
ACDRV ; pin 4

[wrongpolarity]

Thanks for your response and sorry for my late reply. The voltages for U7 are listed below. All voltages are measured with respect to Gnd

ACDET ; pin 6 = 2.59
REGN ; pin 16 = 6.01
VCC ; pin 20 = 18.45
ACOK ; pin 5 = 3.25
ACDRV ; pin 4 = 25.00

Please note that the motherboard is not connected to the battery when the measurements are taken.
Thanks.

[mon2]

You are using a bench power supply and not the official power adapter. This can be the problem since you are not pacifying the adapter detect circuit. Even at the start, the current draw is very low and typical of lighting up a few LEDs.

Would you have a suitable HP branded power adapter?

[wrongpolarity]

Thanks for the immediate response.

I have forgotten to mention that the initial current draw is around 700ma with the lightning of a few LED's when the bench power supply is first turned on. It then drops to the values outlined in post #1 above.

Yes, I have the official HP certified power supply with the center pin. Unfortunately, the behavior of the motherboard remains the same when I use this power adapter.