Lenovo T480 NM-B501 charging but not turning on.

[MARHD]

Hi everyone.

I would like some assistance troubleshooting my laptops fault. It charges the battery (red light on), but does not turn on.

With only the charger connected (board removed from case), I measure the following major voltages:
- VINT20_IN = 20V
- VSYS_OUT = 10.2V
- VSYS = 10.2V
- VDDA = 6v
- VCC5M = 5v
- VL5 = 5V
- VCC3M = 3.3v
- VCC1R0_SUS = 1v
- VCC1R8_SUS = 1.8v

- VCCST = 0v
- VCCSTG = 0v
- VCCCPUCORE = 0v
- VCCGFXCORE_I = 0v
- VCCSA = 0v
- VCC1R2AP = 0v

From this I expect maybe the Switching controller NCP81218MNTXG (PU401) may be faulty.
Am I correct in this assumption? How can I confirm this?

Is there any other voltage I should check?

Thanks

[hopkok]

Did you try turn on without battery, just charger plugged in?

[MARHD]

Yes, sorry I should have mentioned, that is how I am currently testing it. Charger only, no battery, that is how I measured the voltages above as well. I also do not have a CMOS battery if it makes a difference.

[MARHD]

Some additional information. All 4 of the PWM pins of the NCP81218MNTXG (PU401), measure ~1.8V with a multimeter (Don't have my scope with me to check for PWM). But the DRVON pin which should enable the switching FETs, is low. Also, PR415 which is the DRVON series resistor is not placed. Not sure how the switching FETs are supposed to be enabled if this resistor is not present. I'm probably missing something.

[MARHD]

Did some further checks. It seems VCC3B_DRV, VCC5B_DRV, B_DRV, B_ON and A_ON are low. So maybe a faulty ThinkEngine or MEC1653, which would suck.

I will continue testing tomorrow, any further feedback would be appreciated.

[MARHD]

For reference, schematic: https://www.badcaps.net/forum/troubl...71#post1479471

[MARHD]

Could someone explain to me the base requirements for the ThinkEngine and MEC EC to work and enable the cpucore FETs etc. For instance does it need comms from any other IC, or does it just need a particular standby voltage, does the CPU need power from elsewhere, etc. The block diagram doesn't do a good job of explaining that IMO.

[MARHD]

PCH ended up being bad, got another board to try fix instead. Might make another post.