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Old 06-20-2018, 07:10 PM   #1
mgrharry
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Default Lenovo Yoga 910 Charging Problem

Working on a Lenovo Yoga 910-13IKB, model name 80VF. This unit had liquid damage to the USB C DC in board and ribbon that was preventing it from charging properly when the adapter was plugged in. The unit would sometimes not detect the charger at all, other times it would rapidly cycle from charging to not charging (about every 1-2 seconds) when the adapter was plugged in. There was some corrosion evident the DC in board and ribbon so I replaced them both with a new unit however the same symptoms still persist in the form of rapid cycling between charging / not charging. Clearly there is some component damaged on the motherboard itself however there is no visible corrosion or damage to the motherboard itself.

I have a hot air station and microscope so if I can locate the defective component I can probably replace it but I can't locate any schematics for this board and other than haphazard application of freeze spray in the general vicinity of where the ribbon for the DC in board connects, I'm not sure where to start.

You can view photos of the board below.

Any tips would be greatly appreciated.
Attached Images
File Type: jpg mobo_top.jpg (223.0 KB, 53 views)
File Type: jpg mobo_bottom.jpg (111.4 KB, 36 views)
File Type: jpg dcin.jpg (202.1 KB, 46 views)
File Type: jpg dcin_bottom.jpg (117.1 KB, 34 views)
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Old 06-20-2018, 11:46 PM   #2
Stevie2001
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Default Re: Lenovo Yoga 910 Charging Problem


Get it from ebay cheap and very good.
having a dc power supply would be a good thing as it can inejct amps into the bad componant witch will heat up and by using your fingers you can quickly locate the bad part.

Just connect the dc power supply red black to dc then set voltage i to 1v and amps to 0.50 and slowly increase it as your feeling it with fingers,look up on youtube how to use dc power supply to find short.
Thermal camera is best,it takes seconds to locate it and fix it,so in future get this fast.

watch this how to use dc power supply to find short
https://youtu.be/CW87dyYIimE?t=8m44s
time 8:45

You mentioned you have freeze-spray spray one side and connect the power wire and se witch part on board gets visible first assuming the board is iced up.



you can buy cigeratte lighter petrol $1
and add it one one side of the board connect power and se witch part gets dry fast.
the good thing about this is it don't evaporate quicky and also when the petrol is over a component and its bad it will dry up than when you unplug the ic will get covered with petrol again automaticly like jelly very works good.

watch this and so it helps
https://youtu.be/CW87dyYIimE?t=10m
time 10.00

Last edited by Stevie2001; 06-21-2018 at 12:08 AM..
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Old 06-21-2018, 12:34 AM   #3
BlueMidnight
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Default Re: Lenovo Yoga 910 Charging Problem

You never explicitly stated whether it powers up on either battery or AC adapter power. In other words, is the board dead or does it simply not charge properly?
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Old 06-21-2018, 06:48 AM   #4
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Default Re: Lenovo Yoga 910 Charging Problem

Dear mgrharry, start with pwer fets just after dc jack. Check the mosfet datasheet and see whether you are getting correct gate voltage on pin4 of fets. next to check is charging ic voltage. You can download datasheet for charging IC and help yourself in diagnosis. Non availability of schematic is not the end of road in troubleshhoting as long as you are focussed and keep your head cool.
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Old 06-21-2018, 09:42 AM   #5
mgrharry
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Default Re: Lenovo Yoga 910 Charging Problem

Yes, the system powers up and runs off battery no problem. I do have a DC power supply but I'm not sure where on the motherboard to apply power.

Here are some pics with the DC in board and ribbon connected.



Negative clamp applied to ground obviously but where to apply the positive clamp?

Last edited by mgrharry; 06-21-2018 at 09:56 AM..
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Old 06-21-2018, 10:15 AM   #6
mgrharry
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Default Re: Lenovo Yoga 910 Charging Problem

One more thing I noticed: the system will not power on or show any signs of life when AC power only is connected. However if the battery is connected and then the AC adapter is connected the charging light on AC adapter board starts blinking and the system powers on by itself.

Last edited by mgrharry; 06-21-2018 at 11:39 AM..
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Old 06-21-2018, 11:56 AM   #7
mgrharry
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Default Re: Lenovo Yoga 910 Charging Problem

I don't see any mosfets in the immediate vicinity of where the DC in ribbon connects but here's a pic of the closest ones


Application of freeze spray to these doesn't reveal any obvious faults.

Spec sheets can be found here:
https://www.digikey.com/product-deta...5-1-ND/3061123
and here
https://www.digikey.com/product-deta...506-ND/3973606

Last edited by mgrharry; 06-21-2018 at 11:59 AM..
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Old 06-21-2018, 01:29 PM   #8
Stevie2001
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Default Re: Lenovo Yoga 910 Charging Problem

With a normal plug you cant do nothing.
Dc power supply is needed to carry out the repair.
Dc power has the ability to detect short on motherboards and shows you how much amps current or voltage taking.
It also injects amps current into the board and the bad component will heat up you can use freezespray at this point or fingers or thermal camera.


A normal charger has protection and it cannot do this and using freeze spray at this point will not work but works with thermal camera.

Rather then messing about put it aside till you get a dc power supply

Last edited by Stevie2001; 06-21-2018 at 01:36 PM..
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Old 06-21-2018, 01:38 PM   #9
Stevie2001
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Default Re: Lenovo Yoga 910 Charging Problem

Take pic of pu3 ic close
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Old 06-21-2018, 03:04 PM   #10
mgrharry
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Default Re: Lenovo Yoga 910 Charging Problem

I do have a DC power supply but need some guidance on where on the motherboard I would inject power.
Here's a close up of PU3
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Old 06-21-2018, 03:48 PM   #11
Stevie2001
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Default Re: Lenovo Yoga 910 Charging Problem

Take picture of adapter wire main ac wire.
The pins i need to se colour of the wires.

Normally their is red and black wire coming from adapter to the pcb jack.

Remove laptop adapter dont need it.

Not sure what type of dc power supply you have set voltage and amps to 0.

Short the gnd and red of dc power supply then set amps to 0.40 after that unshort wire.
Now set 1v.

Dc power gnd connect to gnd pin of power jack
Dc power red to red pin jack.

Dont connect red permenantly yet just quickly touch it and se.
if the amp dont exceed 0.40 and if it stays on that or below your ok.

Now once your happy connect red and use finger all over board to find heated part check both sides if you dont feel heat increase amps very slowly dont go above 2amps it may fry the bad part.

Last edited by Stevie2001; 06-21-2018 at 04:19 PM..
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Old 06-21-2018, 05:00 PM   #12
mgrharry
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Default Re: Lenovo Yoga 910 Charging Problem

This model charges via USB which is on a separate daughter board connected by ribbon to the mainboard. There are photos a few posts above. Here's a close up of the USB C charging port
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Old 06-21-2018, 05:15 PM   #13
BlueMidnight
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Default Re: Lenovo Yoga 910 Charging Problem

This board works, but has a problem related to the AC adapter input. There is no evidence of a short to ground as yet. No multimeter measurements have even been done. You must do your basic measurements first.

The battery and AC adapter current sense resistors are a good place to start since they are easy to find and we know what they are for, even without access to a schematic or boardview.

The current sense resistors are labelled PR53 and PR57, and are indicated in the attached picture.

Additionally, there is a white fuse on the back side of the power/USB board, near the USB port, labelled PF2001.

Measure the voltage on all 3 of these points in the following 3 situations:
- With only the battery connected
- With only the AC adapter connected
- With both the battery and the AC adapter connected

This should tell us which sense resistor is part of which circuit, which power rail the rest of the board uses, whether the AC adapter voltage is successfully negotiated up to 20V via the USB-C port, and how the input and battery FETs are behaving in the different scenarios.
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Old 06-22-2018, 12:03 AM   #14
Stevie2001
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Default Re: Lenovo Yoga 910 Charging Problem

Quote:
Originally Posted by mgrharry View Post
This model charges via USB which is on a separate daughter board connected by ribbon to the mainboard. There are photos a few posts above. Here's a close up of the USB C charging port
Not sure what is max input voltage but set dc to 1v.
Find out witch pin is plus
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Old 06-22-2018, 07:54 PM   #15
mgrharry
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Default Re: Lenovo Yoga 910 Charging Problem

Quote:
Originally Posted by BlueMidnight View Post
This board works, but has a problem related to the AC adapter input. There is no evidence of a short to ground as yet. No multimeter measurements have even been done. You must do your basic measurements first.

The battery and AC adapter current sense resistors are a good place to start since they are easy to find and we know what they are for, even without access to a schematic or boardview.

The current sense resistors are labelled PR53 and PR57, and are indicated in the attached picture.

Additionally, there is a white fuse on the back side of the power/USB board, near the USB port, labelled PF2001.

Measure the voltage on all 3 of these points in the following 3 situations:
- With only the battery connected
- With only the AC adapter connected
- With both the battery and the AC adapter connected

This should tell us which sense resistor is part of which circuit, which power rail the rest of the board uses, whether the AC adapter voltage is successfully negotiated up to 20V via the USB-C port, and how the input and battery FETs are behaving in the different scenarios.
OK, here's the results:

BATTERY ONLY:
PR53: 7.76
PR57: 0
PF2001: 0

BATTERY + AC
PR53: switches between 7.76 and 8.3 as charging light blinks
PR57: switches between 19.93, no reading, and 2 as charging light blinks
PF2001: jumps around between no reading, .4, 2, and 19

AC ONLY
PR53: switches between 3.8 and 2.5
PR57: 4.61
PF2001: 5.08
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Old 06-23-2018, 06:53 AM   #16
BlueMidnight
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Default Re: Lenovo Yoga 910 Charging Problem

Interesting...

Okay, so that clears up some things. I've attached drawings of two main types of input/charging circuit.

In type number 1, the board is powered by either the AC adapter or the battery. In other words, the main power rail will be at AC adapter voltage or at battery voltage. And there is a separate battery charging circuit (a buck regulator) that only sends current to the battery.

In type number 2, the board is powered by either the battery or the buck regulator. When the AC adapter is connected, its only job is to provide power to the buck regulator. When the buck regulator is functioning, it provides power to the rest of the board as well as power to charge the battery.

Your board appears to be a modified version of type number 2 and is illustrated in the last drawing.

PQ8 seems fine, but one of the other FETs in the drawing may be bad. There could also be an issue with the controller chip. I believe that might be PU4 (an Intersil chip located next to your red circle, in the corner of the board). I can't read the markings on the chip in that photo though, so those would be helpful.
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File Type: png 3.png (32.2 KB, 28 views)
File Type: png 4.png (45.0 KB, 30 views)
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Old 06-25-2018, 02:26 PM   #17
mgrharry
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Default Re: Lenovo Yoga 910 Charging Problem

Here's a pic of PU4
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Old 06-25-2018, 02:44 PM   #18
mgrharry
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Default Re: Lenovo Yoga 910 Charging Problem

At this point if I wanted to try using the DC power supply to inject amps to the board to try to identify the defective chip would I place the positive probe on pin 4 of PQ19?
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Old 06-25-2018, 04:06 PM   #19
BlueMidnight
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Default Re: Lenovo Yoga 910 Charging Problem

Ah okay, so it's an Intersil ISL9237HRZ. And the datasheet confirms a suspicion I had about PQ19 and PQ20. They can be used to boost voltage when the input voltage is lower than required. Anyway.. back to your issue..

You don't want to inject voltage anywhere... much less on the gate pin of one of the FETs. You have no short to ground. You are measuring positive voltage everywhere (even though the readings change from moment to moment). What you do want to do is measure voltage on all pins of PU4. Hopefully this will tell us whether PU4 is acting up, or if it's one of the FETs, etc. This may be made more difficult due to the readings jumping around, however.

Also, have you tried a different AC adapter or tried this adapter on another notebook? Because that can also be the culprit.
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Old 06-25-2018, 04:11 PM   #20
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Default Re: Lenovo Yoga 910 Charging Problem

Have you closely inspected inside the motherboard DC-in ribbon connector
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