Lenovo Thinkpad X240 missing CPU vcore voltage

[stevespc]

I am working on this laptop Thinkpad X240 that sometimes operates normally sometime times fails to P.O.S.T.
When it fails to boot I have found all rails to be good except CPU VCORE which is missing. I traced it to a missing PWM signal on VT1329M. Inputs of 3.3v and 1.8v are good, VR- enable is good.

Not sure about VIN_UVLO which is at 0.5v and 5v before resistor, since this is low voltage lock out could be an issue.

Not sure about CPUCORE_PWRGD, it has 3.3 on resistor R1000 but nothing on Pin 21.

When in normal operation I get 0.68v on pin1 PWM_1

[zaffar]

Re: Lenovo Thinkpad X240 missing CPU vcore voltage

I have the exact same issue on a Lenovo X240 MOBO. I have 1.8v, 3v, and 5v across each of the inductors. I am missing voltage on coils L1, and L7. On the driver chips of each missing voltage point, the voltage required to drive is present.

There are no shorts on the board, nothing is overheating, and ThinkCentre and smsc chips are warm to the touch.

U16 and U2 both have their supply voltage present.

Let me know if I am not making any sense or if I have missed anything.

My issue occurred ever since the laptop was powered on by the charger that came with it. The power and ground were reversed.

Hoping someone can give some advice.

[akuma6099]

I'm working on an x250 with the same problem. Symptoms are keyboard lights up and goes off, CPU fan comes on for 5 seconds, solid green light on the power button and no display. No other indicators. If I press the power button for 1 second I hear a quick pop from the left speaker. Press power again and the cycle repeats itself. Removed RAM and didn't get any beep codes. Dumpped the BIOS and reprogrammed with a known good one for the 20CL, NM-A091, N10RN04W just in case but no change. Reflashed with my OEM dump and started probing. No shorts. I have 20v, 5v, 3.3v, 1.8v rails. All MOSFETS are good and triggered except for the one right next to the docking port which is fine and appears to be normal.

Grabbed a boardview and schematic and started poking around. I found U2 with CPU_ON signal coming from the massive Thinkpad IC U23, pin 84. This should trigger the U2 VT1328MF to output on PWM_1 which feeds U16 VT1334S pin 7, and that chip is responsible for providing CPUCORE_VX1 on pins 13, 14, 15, 16 which feeds L1. L1 pin 2 = VCCCPUCORE and confirmed no power on caps C6400, C6403, C6406 and a few more. Just ordered a VT1328MFQX from Ali. Hopefully this resolves the issue.