Thinkpad Edge E540 missing PM_SLP_S5# and VM_PWRON

[maneatingmonkey]

Hi, I'm seeking the knowledge of repair wizards familiar with Thinkpad power on sequences.

The symptoms are that when the power button is pressed, the red light comes on, but there is no other activity.

The +3VALW and +5VALW rails are present, but none of the subsequent voltage come up. No shorts on inductors or anything obvious like that. EC_RSMRST#, PBTN_OUT# and +RTCVCC are all present, but there is no PM_SLP_S5# or later signals.

I also do not get a VM_PWRON signal. I believe this is needed to enable initial power to the BIOS chips, which are not getting any power ATM. I found the attached sequence diagram from another Thinkpad, but there is no VM_PWRON on that model.

Does anyone know if VM_PWRON is supposed to come on before or after PM_SLP_S5#? Or should this signal be present before I even press the power button?

[Mod. Edit-Vesko356] Schematic and boardwiew: https://www.badcaps.net/forum/showth...53#post1235553

[mon2]

Re: Thinkpad Edge E540 missing PM_SLP_S5# and VM_PWRON

Remove all power. Meter in resistance mode.

What is the resistance to ground of VM_PWRON ?

Meter in DIODE mode.

Red meter probe, yes red to ground.
Black meter probe to VM_PWRON.

What is the reading?

[maneatingmonkey]

Re: Thinkpad Edge E540 missing PM_SLP_S5# and VM_PWRON

Resistance: 91kΩ (black on ground)
Diode mode: 700 on the dot (red on ground).

[mon2]

Re: Thinkpad Edge E540 missing PM_SLP_S5# and VM_PWRON

So there is no short but output is not correct.

The EC at ue1 has an internal 8051 style micro that requires valid firmware to boot. Perhaps the firmware is corrupted. Not a pro at the EC area so wait for other comments. I think you need an external tool to reflash the firmware. That may fix this fault.

Another idea is to review the parts this line enables to see if you can manually enable them. However this takes away the proper sequencing of the power rails.

The downstream devices are load switches / buck regulators that enable by this signal.

Do see that there are some 0 ohms resistor / solder blobs that could be removed and then the EN can be tied to the 3VALW rail to enable.

Ideally you want the EC to enable these parts but the above is an idea for testing.

[maneatingmonkey]

Re: Thinkpad Edge E540 missing PM_SLP_S5# and VM_PWRON

If I tie VM_PWRON to 3V then the downstream devices (SPI chips, +1.05VMP rail) get power as expected, but that's it. However, if I instead tie PM_SLP_S5# to 3V, then the laptop actually POSTs when I press the power button.

PM_SLP_S5# is sent from the PCH to the EC.

Question 1: How can I isolate if the problem is with the PCH or further upstream? What input signals does the PCH need to assert PM_SLP_S5#?

Question 2: How bad of a workaround is it to leave PM_SLP_S5# connected to 3VALW?