ThinkPad T470 does not power up with CMOS battery attached

[rumpumpel1]

I have a ThinkPad T470 that will not boot when the CMOS battery is plugged in.
With only the fan, a RAM module and a USB-C monitor attached, but no CMOS battery, it starts up normally, i.e. after about 90 seconds and two reboots, it stops with a message to press F1 to enter date & time.
If the power is switched off and a CMOS battery is inserted, it restarts as described above. However, after switching it off and on again, it does not turn on. It draws almost no current and shows no sign of life.
I used a different CMOS battery and checked the components around the battery socket, they all look fine. RTCRST to GND is 1 MOhm. I then flashed a cleanME BIOS and finally a BIOS from another working T470. None of this has helped.
Any advice is welcome.

Schematic is here https://www.badcaps.net/forum/showthread.php?t=78951

[mon2]

Re: ThinkPad T470 does not power up with CMOS battery attached

Remove all power. Meter in diode mode.

Confirm the 3 * diodes mated with J12 are not defective.

Meter should conduct in one direction (not the boy band) and block in the other.

[rumpumpel1]

Re: ThinkPad T470 does not power up with CMOS battery attached

yes , I also checked these three diodes. They are ok.
They show a voltage drop of 0,3V and a resistance > 1 MOhm in the other direction.

[reformatt]

Re: ThinkPad T470 does not power up with CMOS battery attached

Check voltage at PWRSWITCH. It routes also to the docking connector, and I've had this cause issues on a X1 Carbon. In that case, I knew that it had had some liquid at that end of the board. Ultrasonic failed to remove it, putting a bit of heat/flux on the pins moved it though without having to take off the connector.

[rumpumpel1]

Re: ThinkPad T470 does not power up with CMOS battery attached

PWRSWITCH always has 3.2V.

[velectronics]

Re: ThinkPad T470 does not power up with CMOS battery attached

Hi,
Check your Power Button maybe it's faulty