Yoga 700 11ISK multiple shorts

[MichR]

I've got this Yoga laptop for a reasonable price. Seller said it suddenly turned off. However, he or someone else tried to repair it, making the situation even worse: he told me the NPCE388 has been replaced, but nothing else was done.
Actually, some power supply jumpers have been desoldered. Sadly, all of these rails are shorted to ground.
Before going on, take a look at the motherboard. This is the best quality picture I could find of it:


And this is a particular of my board:


I could not find any schematics of this board over the web. Luckily, I could find many similarities with the Yoga 3 motherboard, whose schematic I attached in this thread (look below).

Thanks to this document I could name the shorted rails, which you can see in the image above in red text.

I tried to supply the board with a constant current generator in order to isolate the short (up to 1A, with about 0.5W dissipated from the board). Sadly, I could not notice any component heating up. Actually, some of them warm up, but not that much, and I don't want to break anything since these boards are quite expensive.
I also tried to desolder the EC since, according to schematics, many rails are going there and previous owner has replaced it, but the result didn't change.
So I am looking for some help to isolate the issue.

What's more, in the nearby of the EC there is a 3A linear regulator (APL5930). By comparing my board to the new one I could state that some of the components (in particular, configuration resistors that sets the output voltage and the output filter capacitor) are missing or misplaced.
A pull-up resistor for the EC is also missing, but I've already placed a new one there.
According to schematics, the two configuration resistors must be 1.54k and 1.74k. I could find the 1.74k in the correct position, but the two in the red circle are 10k (probably the pull-up resistor) and a 2.2k, which doesn't make much sense when calculating output voltage (I would get 0.8*(1+2.2k/1.74k)=1.81V, while with the schematics values, 0.8*(1+1.54k/1.74k)=1.51V). Also there's a 1nF capacitor, while in the schematics is used a 10nF one.
If any with a similar board could measure the resistors and tell me the value will be really helpful. If not, at least please confirm that the generated voltage is 1.5V so that I can put a new 1.54k resistor there.

Thank you

[mcplslg123]

Re: Yoga 700 11ISK multiple shorts

Putting up missing components is very difficult without schematics or exact same mb. However, That's secondary but priority should be to remove shorts. Without short removal, no point in pondering over the values of missing parts.

[MichR]

Re: Yoga 700 11ISK multiple shorts

Thank you for your prompt response.

I know this is secondary but it was the first thing I noticed when i disassembled the laptop. However, I am still focused on finding the shorts.
I searched online some information about the ICs on the board, looking for one that may be the culprit. I could not find anything related. However, I found the schematics (attached below) of another Lenovo notebook that uses the same audio codec (Realtek ALC3240). According to it, the IC is powered by +3VALW and +1.8VS (the Yoga 3 schematics had 1.5VS!). So it's probable that the resistor I found (2.2k) was the correct one.
Also, this makes it a good candidate for shorts, since two of three rails converge there. I will check it better.

[khaahk]

Re: Yoga 700 11ISK multiple shorts

I have a b921 on my table, check for +5v short (if you have one) on U52 and U2905. Also the npce388 might need to be programmed to function correctly if you resolve the shorts.

[MichR]

Re: Yoga 700 11ISK multiple shorts

No shorts on +5V, but I checked anyway - nothing. However, I found pins 1 and 4 of D45 are shorted to ground, so I decided to desolder it. Differently than Yoga 3, these are connected to a pair of differential lines, much probably U2DN1, U2DP1 (USB 2.0 pair) if I follow Yoga 3 schematics.

I believe this is sufficient to state that CPU is the issue here. What do you think?

[khaahk]

Re: Yoga 700 11ISK multiple shorts

if the diode is gone and usb data lines are short to gnd then sadly yes.

[MichR]

Re: Yoga 700 11ISK multiple shorts

That's a pity. Is there anything I could do? May a reflow be of any help?

[khaahk]

Re: Yoga 700 11ISK multiple shorts

No, only change of cpu, but you don't know what else is burned on that mb. It is not reasonable to continue this repair.

[Stevie2001]

Re: Yoga 700 11ISK multiple shorts

1: test the caps
2: test transistors
put black probe on gnd and use red on them pins if both side beeps its bad for caps.
transistors se if 3 legs short with gnd.

the mofsets look at the code google the datasheet and check the pins and ignore the gnd pins and test if other pins is short with gnd.

if you have dc power supply it will help to inject amps to find heat.
check dcin mofsets
JDCIN1

U2905
Q2421
PD103
PD105
PQ101
PQ102
PQ103

[SMDFlea]

Re: Yoga 700 11ISK multiple shorts

@stevie2001 , if you take the time to read the whole thread you`ll see that the problem has nothing to do with the mosfets, its a different problem altogether, and...these guys know what they`re doing .

[MichR]

Re: Yoga 700 11ISK multiple shorts

No, only change of cpu, but you don't know what else is burned on that mb. It is not reasonable to continue this repair.

Thanks. A new CPU costs about 60USD, but I don't have the tools to replace it. I thought a reflow could have helped if the shorts are among BGA balls, but I cannot be sure. The only option left is to buy a new motherboard, which costs more than 150USD. In my opinion it's way too much for such a board.
I think I'll have to sell the whole laptop as is.

[piernov]

Re: Yoga 700 11ISK multiple shorts

Full short to ground are not caused by the solder balls but rather by the die itself that's internally shorted.
Better throw that motherboard in the trash.

[MichR]

Re: Yoga 700 11ISK multiple shorts

Full short to ground are not caused by the solder balls but rather by the die itself that's internally shorted.
Better throw that motherboard in the trash.

Alright.


A last thought for whoever stumbles across this thread: Yoga 3 motherboard (LA-B921P) should be compatible with Yoga 700. Form factors look the same and connectors are disposed in the same positions (Yoga 700 - Yoga 3). Also, lower and upper cases, as well as all the daughter boards, are the same for both! (I checked in the maintenance manual).
Even if CPU is a bit worse in performance, it may give more runtime on battery since it's 5270mAh (Yoga 700) vs. 4650mAh (Yoga 3)

[tomodachi]

Re: Yoga 700 11ISK multiple shorts

Just in case if someone come across to similar case like 3VALW dead short, they can be sure they need a new board cuz their CPU is toasted.

[MichR]

Re: Yoga 700 11ISK multiple shorts

Alright.


A last thought for whoever stumbles across this thread: Yoga 3 motherboard (LA-B921P) should be compatible with Yoga 700. Form factors look the same and connectors are disposed in the same positions (Yoga 700 - Yoga 3). Also, lower and upper cases, as well as all the daughter boards, are the same for both! (I checked in the maintenance manual).
Even if CPU is a bit worse in performance, it may give more runtime on battery since it's 5270mAh (Yoga 700) vs. 4650mAh (Yoga 3)

Here I am some months later. I finally bought a new Yoga 3 motherboard and replaced the old shorted one. I must tell you that:
- a Yoga 3 sensor board must be bought, otherwise the screen won't automatically rotate nor dim. This is mainly caused by the different accelerometer chip used in these two computers.
- the measured capacity of the battery is exactly the same specified in Yoga 3 battery, regardless of the extra available capacity of Yoga 700 battery.

Another issue is caused by WLAN whitelisting in BIOS. After some hours I came up with the attached modified BIOS. It is based on a clean BIOS file (extracted from the setup file from Lenovo website) and removes whitelist and the BIOS flash descriptor lock. The original BIOS had this lock which prevented flashing the BIOS via Intel FPT utility, so in order to flash the modified BIOS you must use a SPI programmer.

Included in the attached archive are the original BIOS and EC files.