
How to repair the parts that explode in Lenovo yoga laptops - adammunich
https://adammunich.com/how-to-repair-the-parts-that-explode-in-lenovo-yoga-laptops/
======
mindslight
> _It is very likely that the reason the transistor failed was because of poor
> cooling, as it is a low cost, high-resistance transistor that is running
> near its design limits._

This wouldn't be my first guess based on that hole, which was formed more
abruptly than a little overheating. Cooling the outside of the package is only
going to buy a little more margin, not fix the root problem.

Looking at that schematic snippet, what is up with the capacitance on that
gate drive circuit? They want a slower turn on to avoid a popping sound? Maybe
it's a reference circuit that worked fine with a larger package or something,
and a UF6 doesn't have enough thermal mass? If the turn on/off time is the
problem, removing one of C489 or C530 could stop it from happening again.

Or it could be something downstream drawing too much power on that rail or
shorting it out. Since you're replacing the part, you might as well just use a
FET with a lower resistance and some hope to address this possibility.

FWIW some thinner flux (like a Kester 951) will generally let you fix solder
bridges without starting all over.

~~~
laydn
I've commented elsewhere on the thread, but, this also has the potential to be
destroyed by software. That AUDIO_PWR_EN appears to be a signal that can be
controlled by software. If you switch it fast enough such that the MOSFET is
kept mostly in the linear region (due to the RC on the gate), you can kill the
MOSFET very quickly.

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joecool1029
Insufficient cooling has given me issue with certain Lenovo thinkpads over the
years. Most recently it was throttling on a X220, fixed by swapping to a
redesigned fan/heatsink.

The first time for me was with their T43. This model was mostly a platform
refresh of the T42. There's a chip called a southbridge that's located below
the palmrest. Between the models this chip went from 400mhz to 533mhz. Lenovo
decided it wasn't important to improve the cooling, no heatsink whatsoever
included on the southbridge. However, they kept ample temp sensors in the case
so the fans would pulse nonstop as it failed to cool this one chip.

I had two nicknames for that laptop. The 'nut roaster' and the 'vacuum
cleaner'. I eventually fixed the problem by hammering out an old copper penny
and sticking with thermal compound to bridge the gap between the heatsink and
chip. It wasn't perfect but it dropped the temps like 10C. The rest could be
controlled with an installed fan daemon.

~~~
aljarry
I have similar problem with T420s from 2012 - great laptop, but there's a lot
of coil whine and horrible fan with very small heatsink. It's a model without
dedicated GPU, but i5 alone is enough to push the fan to constant medium-high
speed and it's still 70-80°C running Windows 10 with Chrome. Repasting or
cleaning the heatsink does not seem to help.

~~~
leni536
I have a T420s but with an optimus configuration. The dedicated GPU is pretty
much useless because of thermal throttling and yes, even the i5 alone is often
enough to go into throttling territory. This is after repasting and thorough
cleaning of the fan assembly. And if you want to access the fan assembly then
prepare taking apart the whole laptop.

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rarecoil
> It is very likely that the reason the transistor failed was because of poor
> cooling, as it is a low cost, high-resistance transistor that is running
> near its design limits. To prevent the problem from re-occuring, a soft /
> deformable silicone heat transfer pad can be applied to sink excess heat to
> the aluminum shell of the computer. In the 1990s, this was a very popular
> way to keep the motor controllers in CD-ROM drives cool without any
> additional hardware.

So it seems like the problem is a cooling issue, which doesn't surprise me.
"Ultrabooks" often seem to sacrifice decent cooling for the sake of thickness,
and I think it is because most people really do not tax their hardware all
that much. If you do - and you do not have a proper workstation-class laptop -
you're likely to run into similar issues.

My Thinkpad X280 suffers from poor cooling that quickly leads to throttling,
even undervolted. My old work A485 wasn't that great, either.

~~~
rasz
No, cooling is _not_ the issue,. This is not a power transistor, its not meant
to pump a lot of amps. Whats more once its turned ON its internal resistance
is insignificant (225mΩ).

What can be happening here:

\- badly designed output Audio section shorting power in some rare
circumstances, might be as weird as mechanically stressed audio jack touching
traces underneath it.

\- software glitch around audio power enable routine enabling/driving that
transistor hundred/thousand of times per second (pwm) in some circumstances,
_keeping it in the linear region_

\- badly designed under powered mosfet driver, either voltage too low or not
enough current _keeping it in the linear region_

You do not cool power rail switches like this one, they arent meant to
dissipate any meaningful power when designet properly.

~~~
rarecoil
So the author is wrong in his conclusion? I am happy to know the correct
answer.

~~~
dfasdfasd
The author's solution may still help somewhat, but yes, they are almost
certainly wrong. This transistor really just isn't being driven properly,
because it really shouldn't generate heat in this application.

It could a whole slew of problems and it's impossible to tell without
measuring. But, I would guess that gate voltage is not far enough above the
threshold to drop the Rds(on) to it's low loss on-state.

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omgtehlion
Something strikes me in the middle of the article. If you have metcal station
(expensive pro stuff), clearly you have to have some experience with SMDs...
This transistor is replaced with preheater and a hot air gun in seconds, and
it is not the smallest package out there.

~~~
adammunich
It's risky to use hot air spot-heating a high density multi layer PCB, as
these boards aren't really designed for differential heating and can
delaminate easily.

You really should heat the whole board uniformly to be safe, but that is a
danger to do when you aren't sure of the melting temperature of the solders
used.

~~~
omgtehlion
You set preheater to 120c and hot air with smallest nozzle to 240c, works 100%
like a charm

~~~
jve
Do you still need to apply flux before desoldering?

~~~
omgtehlion
You need it while desoldering, while cleaning nopb solder (yes, you have to
clean, or joint will crack later), and while soldering in the replacement.
Flux is cheap, better use it all the time.

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theon144
Safe to say this is way out of technical capabilities of the average (power)
user; but kudos for documenting the process nevertheless! Maybe someone in a
local hackerspace would help out...

~~~
adammunich
Sudo room in Oakland California!

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lnsru
It’s a typical thing in industrial design to conduct the heat to metal
enclosure. I did this for transistors in a stepper motor driver and for FPGA
designs. The cost of conductive sheet is close to zero compared to possible
problems. Lenovo saved this 0,2 cent drop of thermal paste. Maybe it’s worth
producing thousands of consumer devices, though I would like to buy properly
designed products.

Edit: thank you for explanation. This was not thermal problem then. I am just
curious why didn’t all laptops had this problem?

~~~
laydn
That circuit appears to assume that AUDIO_PWR_EN signal will switch very
infrequently.

If AUDIO_PWR_EN is a pin that is controlled by software, and, if you keep
switching that pin such that the MOSFET is kept in the linear region due to
the RC on the gate, that MOSFET will be toast very quickly.

~~~
rzzzt
This is intended to be a power saving feature; if enabled, audio detection
will be driving the enable pin with a few seconds of hysteresis:
[http://www.thinkwiki.org/wiki/How_to_enable_audio_codec_powe...](http://www.thinkwiki.org/wiki/How_to_enable_audio_codec_power_saving)

~~~
segfaultbuserr
Now the problem is, why would a MOSFET be destroyed even if there is a few
seconds of hysteresis?! Well, defective driver is a still possibility, but
perhaps it's a hardware problem.

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garganzol
The damage of this mid-power MOSFET surprises me. Audio circuit is probably
consumes just a few tens or hundreds milliamps at most.

Yet it has a drastic crater-like dent in the IC enclosure. That tells me it
was a voltage surge or current spike.

The hypothesis of entering a linear region caused by a random software glitch
producing an unconscious PWM on a filter slope sounds plausible as well. But
that crater-like dent says that the real cause might be way more intensive
than that.

------
sydd
Lenovos quality crap. We have around 10 Yoga 720s in our workplace, around 7
have their touchscreen/touchpad failed within a year. I'm out of options on
what to buy if I don't want Apple.

~~~
thaumaturgy
Another recommendation: I've been happy so far with my newish LG Gram. There
are some Linux-related issues on some models, but we've found workarounds for
it and compatibility is pretty solid now.

~~~
LocalPCGuy
I've been looking at the Gram, the 17 looks like a pretty nice machine for a
decent price, and going on sale regularly now with the newer i7s out. Worried
about the quality though, and that it'll have similar problems to what the
Lenovos and other ultralights seem to have.

~~~
thaumaturgy
I use mine primarily for software development and systems administration, and
I'm not super picky about things like graphics and audio, so as far as those
things go, I can't say much that would be helpful. Nor have I been running it
long enough to expose the kind of defects that started this whole thread.

Overall though, the laptop feels well built. I like the key action (but
personal preference). The hinge seems to be well made. Nothing flexes when
opening or closing it. The screen, to my eyes, is fantastic, and with the
Celicious anti-glare film on it, it works well in daylight.

It's wicked light. I don't love ultralight laptops and originally was trying
to avoid them, but this one has almost all the ports I want (except for a mmc
instead of sd card slot) and appears to be more serviceable than most modern
non-ultralight laptops. One of the things I looked for was a user-replaceable
battery, and surprisingly, this one should be. We'll see how much it actually
sucks to replace in a couple of years.

If you try to run any Linux on the Gram 17, you _will_ need the info at
[https://bugzilla.kernel.org/show_bug.cgi?id=203617](https://bugzilla.kernel.org/show_bug.cgi?id=203617)

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inflatableDodo
>'If you are not careful you can rip the metal off the circuit board, and if
that happens, there is very little you will be able to do to fix that.'

I've done that before, managed to fix it with silver based conductive paint.

~~~
asteli
One can also scrape the soldermask off of the nearest segment of the trace
that got broken and jumper to it. It's easy to pull up traces on accident but
it's uncommon for that trace adhesion failure to cause the nearest IC pin or
via to fail as well.

~~~
adammunich
Much harder to do with buried vias :-)

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wpskidd
Overheating (and the subsequent throttling) seems to be a growing problem for
Intel. Also, most of their mobile line is locked to the UHD 620 GPU.

As I understand it they are working off of an older fab than AMD and are
hitting its EOL, all while commanding a price premium. AMD has room to expand
their lead and appears to be beginning to, despite being a 10x smaller
company.

------
zelon88
Yikes! Placing alcohol and tools on the battery like that makes me nervous!

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gmcitter
Hug of death?

~~~
adammunich
Curious to know where in the world you are, the server is working well for me
on the west coast.

~~~
vovvov
Timing out for me in Denmark

~~~
adammunich
I just rebooted it again, working now, clearly we have a bug.

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numlock86
Hug of death?

~~~
adammunich
Hmm, I just rebooted the webserver and it seems fine now.

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huseinreds
Refer to google

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theshrike79
Now imagine these were Apple laptops that had their power circuitry randomly
explode.

The amount of angry tweetstorms, memes and class action lawsuits would break
the internet.

~~~
omgtehlion
Well, they do. Usually you go to the genius bar and get the whole board
replaced for $800+

