Dell XPS 7590 (EDP51/EDB51 LA-H331P)

[Karlfoxman]

Ill give you some background first,

My work laptop had some liquid damage, I tried to repair it but it was proving to be a very long task. So I bought another motherboard (Faulty from Ebay and decided to attempt to get that one working)

I've made some progress on it, fixed two problems.

No AC charging (Fixed by replacing a resistor around the current sensing)
Missing voltage on NCP81215 VRMP

The power up sequence stops at getting +VCC_CORE, +VCCGT and DDR_DRAMRST#.

I have a scope to look at the PWM outputs to the outputs:

PWM1_4PH
PWM2_4PH
PWM3_4PH

They rise to mid rail, around 2.0v.

I do get the output on +VCCSA around 1.30v so the NCP81215 must be functioning.

I checked the SVID lines, ALERT# goes low for 40ms, SDIO stay's high, SCLK also stay's high. I will post some scope images shortly.

Any idea what could be the problem, or where to check next?

Many Thanks

[Karlfoxman]

Start up signal NCP81215

Channel 1 : Enable Pin 43
Channel 2 : ALERT# Pin 41
Channel 3 : VR_RDY Pin 45
Channel 4 : PWM3_4PH/VBOOT Pin 20



Shutting down signal traces (Can see EN has gone to logic 0 first.

I checked the timing on UZ21, a MC74VHC1G08.

Input B = IMVP_VR_ON
Input A = SIO_SLP_S3#
Output Y = VR_ON

SIO_SLP_#3 de-asserts, that is why the VR_EN is going logic low. Question is, why is SIO_SLP_#S3 going low? Is this because the +VCC_CORE is not present in time?