ThinkPad T14s Gen 1 (NM-C891) no power, I could use some help with the troubleshooting

[mrfree2ita]

Hi all, I'm thrilled to finally be able to close this thread! I managed to fix the issue and everything is working perfectly now.

A massive thank you to everyone who jumped in, offered suggestions, and helped me troubleshoot. This community is just incredible, and I genuinely appreciate the time you all took out to help me solving this puzzle.

In case someone else ends up here facing a similar problem, I want to leave a few additional observations. Hopefully, this saves someone else a bit of headache down the line!

• The ThinkEngine (BD4179MWV) does not need to be programmed when replaced
• The white LED on the power button blinking three times when plugging the AC adapter in it turns out to be totally normal. I noticed it, by chance, on another T14s. This pushed me away from the solution for quite sometime, since it made be suspect issues with the MEC EC
• Once the previous point was cleared, I went back to my suspect that a misalignment between EC and BIOS could prevent the board to start correctly. Unfortunately, in my case, the person who previously tried to fix the board removed the BIOS chip and didn't bother putting it back on, so I was not able to find any clue about the original BIOS version. I tried a couple of BIOS dumps I found on this forum and on another community channel but without success. Eventually, the one shared on this post did the trick for me! (it's a N2YET35W v1.24)
  
  After I fixed the board, I confirmed that the EC runs version 1.08, hence I needed a BIOS version >= 1.15
  In fact, from Levovo BIOS changelogs for this model:
  
  

  UEFI: 1.15 / ECP: 1.08
  - (New) (Note) If the UEFI BIOS has been updated to version 1.15 or higher, it is no longer able to roll back to the version before 1.15.
  - (Fix) Fixed an issue where wrong battery remaining percentage might be shown.

Man, it feels so good!

[mrfree2ita]

Recently, I had the same problem, and it was resolved by flashing the EC controller and selecting the correct BIOS.

Hi there! Thanks for sharing. Honestly, I also considered trying that Provided that I'll be able to find a bin to flash for this board, is it something I could do with a ch341a?

[reformatt]

Forgot about this thread. Are you still working on it? Do you get VSYS15 at all or is the main power rail dead? Have you checked it isn't shorted?

[UADmytro]

Recently, I had the same problem, and it was resolved by flashing the EC controller and selecting the correct BIOS.

[mrfree2ita]

I finally found some time and replaced the dual mosfets.

I replaced both PQ0201 and PQ0202 with their counterparts from a similar board I have (let's call it blue-pcb). The latter has other problems, but the power stage seems fine since it comes up, charges the battery and shows BIOS screen.

Unfortunately, I still get the 3 blinks on the power button white led. So no visible change in behavior.

The blue-pcb donor board keeps working the same way with the mosfets from the board I'm trying to repair.

Any other idea?

[mrfree2ita]

Many thanks for the suggestion. I'll give it a try.

As a matter of fact, I have another board from the same Lenovo generation but based on AMD Ryzen architecture. This part of the board is based on the same BQ charger IC. I'm tempted to take the dual mosfets from there What do you think?

I'd replace the Infineon 0924NDI with SM7360EKQG (more beefy), and the SiZ340DT with AONH36334 (a bit smaller in amps). The latter code is from the schematic, the package is actually marked "M6 VUA 2W0E08" on the board, but I couldn't find a datasheet using this identified. I'm attaching the datasheets for reference.

[mon2]

Both PQ0201 & PQ0202 look too low for me. Suggest to flux and replace both dual mosfets. Before you do this, measure the fresh ones while they are on your work table. You can use the measurements as a comparison of a known good mosfet. Each will be much higher in measurement. Recommendation is to source from tier 1 distributors like Digikey / Mouser / Arrow and only if you must, Aliexpress but select a vendor with very high ratings.

[mrfree2ita]

Here what the PQ0201 shows when off the board:

High side (gate:1 -- source:9 -- drain: 2,3,4)

source / drain	4M
source / gate	OL
gate / drain	OL

Low side (gate: 8 -- source: 5,6,7 -- drain: 9)

source / drain	123k
source / gate	OL
gate / drain	OL

And the PQ0202 (in circuit):

High side (gate:1 -- source:9 -- drain: 2,3,4)

source / drain	160k and raising
source / gate	219k
gate / drain	229k

Low side (gate: 8 -- source: 5,6,7 -- drain: 9)

source / drain	141k
source / gate	201k
gate / drain	340k

[mon2]

The low side mosfet inside this dual mosfet looks to be quite low (87k ohms) for a good mosfet.

Suggest to flux and remove this dual mosfet and test the component while it is on your workbench. Are these measurements still this low on your bench? Each should be hundreds of k ohms or higher. This part may be defective.

Can you measure in the same manner the dual mosfet @ PQ0202? Post your measurements.

Your voltage measurements look good.

[mrfree2ita]

The Dual MOSFET on the board is marked 0924NDI, so it's the Infineon.


High side (gate:1 -- source:9 -- drain: 2,3,4)

source / drain	150k and raising
source / gate	220k
gate / drain	450k and raising

Low side (gate: 8 -- source: 5,6,7 -- drain: 9)

source / drain	87k
source / gate	210k
gate / drain	346k

On the IC charger I find:

pin	name	measure
1	VBUS	20.12v
2	ACN	20.11v
3	ACP	20.12v
28	REGN	6v

[mon2]

My bad...indeed a dual mosfet inside a single package.

However, in the schematic there are 2 part numbers used for this component. Each is a DUAL N-channel mosfet so this implies that the gate voltage must be higher than the voltage being passed betwee source / drain pins to enable.

On the BQ series, the N-channel driver pin should be ~25v and is based on adapter voltage + REGN voltage = 20v + 6v = ~25v to enable the mosfet.

Noting that we do not have this voltage from the BQ charger IC, proceed to test the following pins of interest.

Remove all power. Meter in resistance mode.

Measure the resistance across each mosfet pin:

source / drain
source / gate
gate / drain

of the 1st mosfet inside this package

then repeat for the 2nd mosfet inside this package.

We are checking if there is a low resistance which often means the mosfet is shorted and needs to be replaced. Each measurement should be hundreds of k ohms or higher if normal.

Assuming the resistance checks are ok, carefully review the voltage to ground of the following pins of interest on the charger IC:

VBUS ; pin # 1
REGN ; pin # 28
ACN ; pin # 2
ACP ; pin # 3

See attached for the datasheets for the dual mosfet parts used at this location by the PCBA shop:

[mrfree2ita]

Mhhhh... while I was looking at page 102 for the measurements, I noticed that the -EXTPWR signal is originated there, and it's actually low!

Based on the power sequence from the X270 documentation, -EXTPWR should be the next in line to go up (in the other schematic it's called -EXT_PWR_GATE, but I guess both refer to the same signal)

[mrfree2ita]

On my board, the PQ0201 is a Dual N-channel MOSFET:




Here are the measurements:

pin	measure		pin	measure
1	~400mV		5	0v
2	20v		6	0v
3	20v		7	0v
4	20v		8	5.8v
			9	~308mV

[mon2]

To me, TE is working fine due to this 20v negotiation.

Carefully, measure the voltage to ground on each pin of the DCin mosfet that follows this power path to power the main power rail.

Test the voltage to ground on mosfet @ PQ0201.

Interested in:

source (1-2-3) ; select any pin.
gate (4)
drain (5-6-7-8) ; select any pin.

Post each measurement.

[mrfree2ita]

Yes, I can confirm that the PD negotiation seems to work properly. I tried with the USB-C connector in both positions (and disconnected the AC adapter from the wall as you suggested each time).

In both cases, on the board I can measure 19.8v on pin 45 (VREGIN20) of the TE.

[mon2]

From post # 7 - you have ~20v onboard. If the power adapter is the USB Type C, this confirms that the TE is working since the power delivery contracts have been negotiated with the external USB C power adapter and the power rail has switched from the power on default of 5v to 20v. Can you confirm this detail? The communication is over the CCx pins. There is CC1 on one side of the USB C connector; CC2 pin will be on the other side of the USB C connector.

Turn off all power and unplug the USB C power adapter from the wall - personally do not trust them at all - then rotate the USB C plug to your laptop by 180 degrees. Now plug the power adapter to the AC socket. Do you see ~20v again? If yes, the PD controllers are working.

[mrfree2ita]

The led that shows that pattern (i.e. 3 blinks) is the LED_PWR and it's controlled by the EC (page 85 of the schematic).

[mon2]

To where are the LEDs that blink bonded? Is it the EC or the TE? If the TE, then for sure there is firmware already present inside to offer the blink pattern.

[mrfree2ita]

Think Engine chip is programmable?

I couldn't find any information about this for the ThinkEngine-3. According to the schematics, it can be one of the following:

Vendor	P/N	LCFC P/N
ROHM	BD4179MWV	SA000090J00
TOSHIBA	TC62D518FTG	SA00008E500

Based on my understanding, on this board the EC role is implemented by the MEC1663 (which is programmable) and the ThinkEngine-3. The two chips communicate via SPI.

The EC doesn't seem to be stone dead to me, considering that it should be the one responsible for the blinking pattern on the power led for instance.

Considering that when I got the board the BIOS chip was missing, I bought a new one and flashed a version I found here on the forum. But with or without the BIOS chip on, the blinking pattern doesn't change.

Any idea what I could inspect? I was thinking for instance to sniff the SPI communication with my logic analyzer to see if there's any useful pattern there...

[mcplslg123]

Think Engine chip is programmable?