Thinkpad T480 is dead (nm-b501)

[Darktron]

Hello all,

I tried to repair my T480 motherboard.
The PC can not power off at all.

I tried the USB-C meter on both ports : it's loop on/off. I think I can not negotiate the 10-20V voltage.
I tested with an USB "classic" 5V charger with to USB-C : the USB-C meter displays 5,080 V, 0,02 A with some pics to 2,5 A

The USB-C meter was being tested on other USB-C device, it's works fine.

Thank you in advance for your help.

LINK to Schematic -> https://www.badcaps.net/forum/troubl...b501-schematic

[dmill89]

Hello all,

I tried to repair my T480 motherboard.
The PC can not power off at all.

I tried the USB-C meter on both ports : it's loop on/off. I think I can not negotiate the 10-20V voltage.
I tested with an USB "classic" 5V charger with to USB-C : the USB-C meter displays 5,080 V, 0,02 A with some pics to 2,5 A

The USB-C meter was being tested on other USB-C device, it's works fine.

Thank you in advance for your help.

LINK to Schematic -> https://www.badcaps.net/forum/troubl...b501-schematic

Unfortunately, these models had a known defect on the firmware where the Thunderbolt controller (which controls the USB-C functionality on these) would constantly write to the EEPROM storage for the controller and kill it (too many write cycles). There is a firmware update to fix this you can try, but it won't help if the controller EEPROM is already "cooked" (in which case the only fix is either replacing the Thunderbolt EEPROM chip, or the entire motherboard, some have seen success manually flashing the EEPROM , but that is hit and miss).

Official Lenovo support article on this issue:
https://pcsupport.lenovo.com/us/en/p...dates-thinkpad

Redit thread discussing manually flashing the EEPROM (this is for a T480s but the issues is similar among several models):
https://www.reddit.com/r/thinkpad/co...o_upgrade_the/

[rumpumpel1]

https://www.badcaps.net/forum/troubl...olt-3-firmware

[Darktron]

Hello,

Thank you for your reply.

The thunderbolt firmware was been updated 2 mouths before the breakdown. This previous owner didn't perform the firmware update...
I tried to flash with CH341, not better.

With my voltmeter, I ckecked VCC on the Winbond chip (U15), it's various voltage between 4V and 0V by loop.

I can manage to replace this chip.

[Darktron]

Hello,

I tried to flash the Thunderbolt EEPROM with my Raspberry Pi and FlashROM : the chip works (can erase, write, verify BIN file).
I don't know to check now...

What do you suggest ?

[khaahk]

T480s have a lot of shorted capacitor issues, check page 67 in schematic, measure resistance to gnd on PL1 for start.

[Darktron]

T480s have a lot of shorted capacitor issues, check page 67 in schematic, measure resistance to gnd on PL1 for start.

Hello

khaahk thank you to try to help me.

I checked this :
PL1 pin 1 - GND = 8-10 ohm
PL1 pin 2 - GND = 10-12 ohm

[mon2]

There is a short on this rail. Suggest to flux and remove PL1 and also PL2 since they are on the same power rail. After these 2 parts are removed, measure the resistance to ground again using the SMD pcb pads where these parts were soldered.

Which side of the PCB pads is still shorted? Is it the upstream producer adapter side = PL1 pin #1 = PQ2 side or the downstream consumer side = PL1 pin #2?

My suspicion is that the bad cap will be inside the attached capacitor cluster.