Thinkpad X1 Carbon gen2 (LMQ-1) no power

[Norrecito]

Hello,

After dealing with old video game consoles I'm trying to get into laptop repair (only as a hobby) but maybe I should have taken a smaller step.

Anyway I would like to request some help with a X1 Carbon gen2 (LMQ-1 MB 12298-2 48.4LY05.021 motherboard) I've bought that has no power.

I don't know the history of the laptop but it seems to have a smashed screen (based on the discoloration) and the only work done on the motherboard is with U49. I assume that is the BIOS chip and they either replaced it or just flashed a new BIOS. The soldering seems to be okay there and all legs are attached. (No bridges or anything but I can post pictures if you are interested) I think I was the first person taking out the motherboard of this laptop.

Fortunately in this (very cool) forum, I have managed to find both the schematics and boardview file for this motherboard and together with the information I've found on the Internet I've started troubleshooting...but now I'm stuck.

Both the charger and the docking station that came with the laptop is good (I'm using the docking station because it has a power button that I could use without the keyboard) and the board receives 20V from it. It goes to the "source" legs of Q9 ("FDMC4435BZ", a P-Channel mosfet). "drain" had 0V, so I have checked "gate" which had the voltage of 19.90V which (according to me knowledge) is "high" and means that this mosfet is not turned on.

I assume that the "gate" of this mosfet should be "low" if "DISCHARGE" is "low" and "-PWRSHUTDOWN" is "high". I've checked "DISCHARGE" and it is 0V (Good). Then checked "-PWRSHUTDOWN" but that's also 0V (Problem). "-PWRSHUTDOWN" (coming from U101 which I assume is the Power Management Hub) should turn "high" if "VCC3SW" is present by a pullup resistor. I have checked "VCC3SW" and it's present (3.3V) on the board. Based on the schematics, the pullup resistor is R1101. It's measuring 32.4K.

...and now I don't know what should I check next

Please feel free to correct me if any of my assumptions were wrong. All of them are based on a X230 "no power" motherboard repair I've found.

Some additional information:
- Before taking out the motherboard, I have tried to "reset" the laptop (emergency-reset hole). Also tried to disconnect the internal battery.
- The CMOS battery is depleted..measuring almost 0V. (The laptop does not power on even with the CMOS battery disconnected)

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

Still haven't figured out what causes "-PWRSHUTDOWN" to be 0V but after some digging, I came across a post in a Chinese forum which when Google translated to English has some promising information.

The post starts with the "VINT20" generation sequence. (As far as I know, "VINT20" should be present on a working motherboard when a charger is plugged in but we know it's not present on mine because "CV20" is 0V) What caught my eyes here is every single component (diodes, mosfets, resistors and the chips) that is mentioned in this section has the same marking as in the motherboard (LMQ-1 MB 12298-2 48.4LY05.021 motherboard) I'm trying to fix. Either it has been written for the X1 Carbon or other Thinkpads use the same circuit (more likely to me).

Anyways, it has a section that lists the possible reasons why "-PWRSHUTDOWN" could have no voltage. After Google translating it, it has the following to say:

1. VCC3SW causes the -PWRSHUTDOWN pull-up resistor to have no voltage. If D6 is disconnected, if there is still voltage in VCC3SW, the parts connected to U58 or RTCVCC may be defective. Defective parts connected to C611 or VCC3SW.
2. The thermistor causes -PWRSHUTDOWN to have no voltage. Use an oscilloscope to measure the instantaneous voltage of U101 PIN98 when it is powered on. If there is a voltage, the thermistor is bad. Use a multimeter to measure the resistance of the thermistor to find the bad location.
3. If the above is OK, use a multimeter to measure whether the capacitor C606 and diodes D64, D8, D56, D62 are broken down (the diode is unidirectionally conducting) or the U101 is bad. If the above is still OK, you can pry open the U101 PIN96 to make the PWRSHUTDOWN voltage normal (the VINT20 voltage is also generated normally), and then measure whether the motherboard voltage is abnormal and the maintenance is OK.

1. Not sure if I fully understand this one. Should I desolder D6, plug in the charger and see whether VCC3SW is still present? Is this safe? RTCVCC is present, it's 3.3V. Checked D6 with my multimeter (diode test) and it seems to be okay.
2. A thermistor? I did not find any on this motherboard or I don't know where to look Boardview shows no component marked with TH<number>. I can imagine the battery having one but the battery is disconnected.
3. C606 is not present on this motherboard (even though it also shows up in the boardview), all of the mentioned diodes (D64, D8, D56, D62) are okay.

Feel like I'm missing something pretty basic.

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

Guys I'm definitely making progress...I do have power light now but I have no idea how it happened.

After reading some posts here ("Laptop battery charging circuit") plus a Google translated Chinese post of a Thinkpad T470 repair, I have realized that those Thermistors are marked with RT<number> and there are 6 of them on this motherboard. I've just finished measuring them (They should be 540 Ohm according to the schematics and all of them measured between 557 and 620 Ohms for me) and plugged in the charger so I could measure the voltage on the TH_DET leg of U101 when the fan suddenly started spinning.

Unkown of the further issues, I thought it would be a good time to replace the thermal paste before I start to reassamble things. After taking out the fan, I was shocked to see that someone has cleaned up the original thermal paste but didn't replace it so the CPU had no thermal paste at all...I wonder whether this has anything to do with my "no power" issue.

Anyway, after putting on some thermal paste, I have reassembled the laptop for testing...and it still has problems. When I plug in the charger, the laptop seems like it tries to start but shuts down after a second and it keeps repeating this until I press the power button. After the power putting is pressed, the laptop shuts down and I have power light. If I press the power button, the same thing happens (it tries to start but shuts down after a second) except it only does it once.

Hmm...could this be a BIOS problem? I guess I have some more reading to do.

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

I'm still stuck with the same issue.

Saying the laptop shuts down after one second was an overstatement. It shuts down almost immediately (fraction of a second) after pressing the power button. The power light returns and I can repeat this forever.

Anyway I have two ideas to go forward:
1. I have realized that the resistors marked "R413" and "422" (both are "20R3J-5-LL-GP" according to the schematics) are burned. I haven't noticed this before as "VREGIN20" were present and showing the correct voltage (19.7V). Based on what I've read these are "anti-surge" resistors. They should be 20 ohm each. Of course its impossible to get such resistors locally in my country and I didn't find them on Aliexpress either.
I went with the next best thing which is to get a donor motherboard that has them. Didn't find any X1 Carbon motherboards for sale but it seems like (based on the schematics) other Thinkpads are also using ones with the same specs so I've bought a broken T420s motherboard (no power) which should arrive next week. I hope that I can re-use the ones from there.

2. I'm no longer convinced that this is a BIOS problem. (At least I didn't find any topics which had the same issue as mine and turned out to be a BIOS related thing) but I do have a Raspberry PI 3 model B+ which I've figured could be used to reflash the BIOS so I have bought a SOP8 clips (which should also arrive next week) and could potentially flash a new BIOS.

Still any other ideas you guys have are very welcome

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

The faulty T420s motherboard has arrived and I have successfully replaced "R422" and "R413" with the ones found on this board. Checked the ones removed from the X1 carbon motherboard and one of them measured 12.7 ohms while the other was 15.4 so they were indeed damaged. The resistors extracted from the T420s motherboard were both 20 ohms.

Surprisingly after that I was back to step one: "no power". The gate of Q9 was 19.90V again. So I have measured the voltage on the TH_DET "leg" of U101 and it was 1.2V. (Through the "TH_DTCT_TE" net) According to what I've managed to found, this should be much lower...so I have started measuring those thermistors again (RT1-RT6) but this time I've measured their resistance to ground (because one topic I've found suggested this) and RT1 come up with like 1.2 MEGAohms. Checked the other (RT2,RT3,RT4,RT5,RT6) and all of them were between 0.56k and 3.52k which is much lower. I went back to check RT1 again but this time it was 4.33k...and I have no idea what has changed.

Anyway after the measurements I have plugged in the power supply and the gate of Q9 became 6.68V (from 19.90V), "TH_DET" is 0.30V (from 1.2V) and I'm back to the issue where I was stuck before I've replaced the damaged resistors (The laptop shuts down immediately after I press the power button).

I feel like this board is trolling with me.

Tried to search for similar issues but haven't found any.

Any ideas guys?

[mon2]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

Any chance that you have schematics for this board ?

If not, trace where the power enters the logic board -> review the mosfets and there should be a charger IC nearby.

What are the SMD markings on the charger IC ?

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

Any chance that you have schematics for this board ?

If not, trace where the power enters the logic board -> review the mosfets and there should be a charger IC nearby.

What are the SMD markings on the charger IC ?

Yes I do! Attached both the schematics and the boardview file.

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

If "U7" is the charging IC (tried to find it in the schematics), then the markings on chip are:
"bq
24760
ti 42k
ce05 g4"

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

Is there anything that is worth to be checked near the charging IC? (Or on the charging IC itself)

When the power supply is plugged in, the laptop does not seems to be charging the battery. On the plus of the battery connector, I can recall measuring like 0.6V although I'm not sure what are the prerequisites for the IC to start charging.

[mon2]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

So the 24760 is yet another charger IC built by TI under private label. Must have been as successful as their OMAP processors

The idea now is to review how the 24760 is wired and attempt to review the measurements against other TI charger ICs with public documentation.

See attached on a schematic found that uses this IC.

Start with carefully - very carefully measuring the voltage of the following pins:

ACDET (pin #4)
REGN (pin # 15)
CSN (pin # 11) ; charger current sense
CSP (pin # 12) ; charger current sense

what are the voltage readings ? Red meter lead on the pin; black meter lead to ground. Be sure your probes are fine tip to support these measurements.

Post the readings.

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

First of all, thanks for helping me

Here are the measurement results:

ACDET (pin #4) => constantly changing between ~0.56V and ~0.80V
REGN (pin # 15) => 6.16V
CSN (pin # 11) ; charger current sense => 0.61V
CSP (pin # 12) ; charger current sense => 0.61V

pin#11 is called "CHARGER_OUT12" by the boardview all other pins are having the text (ACDET, REGN, CSP) in their name that you are refering. Might not matter.

I have two things to note regarding the measurements:
- My multimeter tips are not fine enough to measure the legs of the IC itself so I have used test points (that are in the same net) based on the boardview.
- All measurements were made without the battery plugged in. In fact nothing is plugged into the board right now.

I assume that the board should start without a battery but If I'm wrong then I gladly repeat all of my measurements with the battery plugged in. (Yes, I've tried and the laptop wouldn't start even with the battery plugged in)

[mon2]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

The ACDET reading is not good.

Typically, the design will use 2 resistors as a voltage divider to lower the very high voltage (ie. DCIN from the adapter) to a safe value that the charger IC is able to read as a 'good adapter voltage present' value.

So remove all power. Trace back this pin # 4 and locate the 2 resistors that should be close by. One resistor will go to the DCIN adapter voltage.

Then the same pin # 4 will have a resistor to ground. The combination of these 2 resistors = voltage divider.

Use your meter in resistance mode - start with a high scale. Then measure the resistor value that is between this pin # 4 and the DCIN adapter.

Then measure the resistor value between this pin # 4 and ground.

Post both readings. From your readings, we can calculate what the proper expected voltage should be at this ACDET pin.

From the last post, the ACDET is too low for the charger to believe that an adapter is even connected to the logic board so nothing to do...

Late PS: Do you have schematics for this thing? If yes, can you post them here ?

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

Late PS: Do you have schematics for this thing? If yes, can you post them here ?

If you mean the laptop motherboard then I've posted both the schematics and the boardview file in one of my previous posts. I don't have the schematics for the charger IC though.

Anyway what you said in your previous post about the typical design seems to be true for this motherboard.

Pin#4 is connected to "R584" and "R227".

The other side of "R584" is part of "DCIN_PWR20_F" so I think that this is the resistor we are looking for. Measured it and it's 407k. Measured "R227" as well and that one is 64.4k.

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

Okay, I've just realized something important.

I made a leep of faith and (under my microscope) measured the voltage on "R584" (on the side that is connected to the IC) and it's a stable 2.64V. I have no idea how the test point shows a constantly changing voltage under 1V when both are in the same net. Anyway I've learned the lesson, I will measure components whenever possible.

Is 2.64V still bad for ACDET?

[mon2]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

Sorry, my bad - I recall your post from before but into too many threads. That and still not 100% recovered from covid but almost there so that is my excuse

Is 2.64V still bad for ACDET?

This is a good value (based on readings from other TI charger ICs).

Update:

1) Measure and post the readings for the I2C bus lines = SDA & SCL = pins 6 and 7 of the charger IC. The I2C bus is a 2 wire interface used by the host CPU (BUS MASTER) to communicate with slaves (charger ic, etc.) with unique addresses. Using the clock to shift data INTO / OUT OF the slave, the data lines then spit data back and forth to configure the parameters of the charger IC (in this case).

If either of these lines are 'stuck', then no communication can occur.

Interested in the voltage readings of each of these 2 pins. Do measure with care.

2) Next, remove all power. Measure the resistance values on the battery mosfet @ Q35 like before. Post the readings for each combination of the mosfet pins.

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate(4)
gate (4) & drain (5-6-7-8)

Meter in lowest scale. If you see '1' or 'OL' then the scale is too low so use the next scale setting.

Searching for a low resistance = mosfet is defective.

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

You don't even need an excuse, I'm glad you are trying to help. I've been lonely talking to myself for 8 days in this topic

1)

pin#6 => 3.37V
pin#7 => 3.37V

Used test points for both but both are stable 3.37V (Components were in crowded places and it's almost impossible to measure the legs of the chip itself with the multimeter leads I have)

2)

I'm a bit puzzled about this one as the boardview shows that Q35 has 8 legs while I can see 10 when viewing this mosfet from the top.
As the readings are pretty consistent I didn't worry much about it.

source (1-2-3) & drain (5-6-7-8)
1 - 5 => ~14 Megaohm
1 - 6 => ~14 Megaohm
1 - 7 => ~14 Megaohm
1 - 8 => ~14 Megaohm
2 - 5 => ~7.5 Megaohm
2 - 6 => ~7.5 Megaohm
2 - 7 => ~7.5 Megaohm
2 - 8 => ~7.5 Megaohm
3 - 5 => ~9.2 Megaohm
3 - 6 => ~9.2 Megaohm
3 - 7 => ~9.2 Megaohm
3 - 8 => ~9.2 Megaohm

source (1-2-3) & gate(4)
1 - 4 => 476k
2 - 4 => 476k
3 - 4 => 476k

gate (4) & drain (5-6-7-8)
4-5 => OL (even on 20M setting)
4-6 => OL (even on 20M setting)
4-7 => OL (even on 20M setting)
4-8 => OL (even on 20M setting)

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

In addition to the measurements found in my previous post, I might have some good news:
I've managed to find another faulty X1 Carbon gen2 motherboard. According to the seller, it turns on but gives no picture.

I've figured that we can compare measurements between the two boards if we are unsure about some things (assuming it has a different fault). It should arrive this week. It wasn't as cheap as the T420s motherboard I've bought but this one comes with both the fan and heatsink which alone worth the price I've payed.

In the meantime, I've tried to search the Internet and watch (many) laptop repair videos in order to find an issue similar to the one I currently have. The most promising thing I saw was a case where a laptop shut down immediately because it could not detect 5V after being started. But it was a different laptop from a different manufacturer. Not even sure if it applies to this one. Anyways, I've checked "VCC5M" and its present with the charger plugged in. In my case, the fan spins for a fraction of a second after the power button was pressed.

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

Okay it's not the BIOS.

Used my Raspberry Pi 3 to backup the original (16 mb) BIOS from the motherboard and flashed one that is supposedly working (found in this forum) but it is doing exactly the same thing.

I have ran out of ideas for this one. Any help is much appreciated.

By the way, is that charging IC mosfet okay based on my measurements?

[Norrecito]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

The other faulty X1 carbon gen2 motherboard has arrived. Surprisingly it even gives picture. Unfortunately I found out the problem with that one pretty soon. It fails both (Lenovo) memory tests and even freezes when I try to view the log. I assume this is beyond repair but I don't know if the laptop could actually fail these tests without the memory chip being faulty.

Anyway, I now have another board to use as a reference for the startup problem I'm having with the first one. (I really hope that one has no RAM issue)

Any ideas what should I look for?

Neither reading topics nor laptop repair videos give any new ideas to me so I'm kind of stuck right now.

[nstrument]

Re: Thinkpad X1 Carbon gen2 (LMQ-1) no power

Were you able to confirm whether all voltages come up correctly and what they're supposed to be? I'm also tinkering with a broken X1 Gen2 (power button flashes a few times, fan spins momentarily, nothing on screen) and I can't figure out what "VCCCPUCORE" is supposed to be. U16 should be generating it and when I measure the voltage on L1, I get ~1.75V for 500ms after pressing the power button and 0V after that. This seems odd to me since VCore for an i7-4600U CPU is 0.68V, not 1.75V.
The schematic is just calling it "VCCCPUCORE" without specifying the value anywhere. There appears to be no datasheet for the V1334S Volterra IC (U16) either.