Surface Pro 4 doesn't turn on

[youpla]

Hi,
My name is Nicolas, I live in a little town near Paris, France.
I like to try to fix electronic stuff principally game console but I try to change device type.
I bought few days ago an Surface Pro 4 (core i7 cpu, 8Go of memory). Seller told me that I had a lot of difficulties to wake tablet after puting it in sleep mode and one day it was impossible to switch on his tablet.
I managed to remove screen (but I broke it ) and check what if found as common faillure on net :
* charging diode
* bad fuse
* bad it8528g
All my mesurments on this 3 points were fines. Nevertheless I decided to replace the it8528g. I done that by reading this article : https://www.aonemobiles.com.au/2020/...cs-no-problem/
After remplacement, 3.3 volts is present on cap near it8528g, so I think that I soldered new chip well but tablet doesn't switch on.
I decided to mesure some voltages and resistances to check if all rails were presents and if there was no short to groud.
What I noticed with measurements :
* no obvious short
* Battery charge well
* 3.3 volts presents on switch button
* voltage on pin 3 and 4 from buttons connectors (where switch and volume buttons are connected) are fluctated between 0 and 1.78
* others voltages are quiet complexe to explain so I put my measurements on an picture joined with this message.

This varying voltage between 7.5 volts and 8.69 volts seems very strange for me and 1.54 volts on inductor near usb port instead of 3.3 volts is obviously an problem. Fact I have no 5 volts on inductor lying between usb port and display port connectors is also an problem.

Have some advice in order to understand whats happens ?
Wich measurements may I do ?
Where are test points ou points too check power rails ?

Best regards, Nicolas

[reformatt]

Re: Surface Pro 4 doesn't turn on

Surface Pro is not a good place to start to learn these kinds of repairs. There is zero support from MS and there are no schematics.

With no schematics, you have to rely on your knowledge on how these things are supposed to work, and identify what IC does what and then refer to datasheets to check enables/power goods etc. The problem we are finding in the industry now is that a lot of datasheets (especially those from ITE and TI), are no longer being published. So unless it's something simple/obvious, these kinds of boards just become donors.

And that's how the industry wants it. Support Right to Repair!!

[piernov]

Re: Surface Pro 4 doesn't turn on

Surface Pro 4 schematics are available.

[reformatt]

Re: Surface Pro 4 doesn't turn on

Fair enough, haven't checked for ages but stand corrected.

https://www.badcaps.net/forum/showth...pro+schematics

The IT8528 is the Embedded Controller (EC), not a power management chip (which its described as on some sites). There is a external EEPROM for the EC code, so it doesn't need programming. There is a power sequence diagram on pg 5 of the schematic, so this is good place to start.

[youpla]

Re: Surface Pro 4 doesn't turn on

Hello,

Thanks for your replies and your help
Indeed I already founded schematics and boardview for my Surface Pro 4 on this forum.
I will pay attention on pg 5 of the schematic to see if I could find some usefull informations.
As I said, am I an enthousiast not a tech with a lot of knowledge, I am not sure to understand a lot of thinks.

Best regards, Nicolas

[youpla]

Re: Surface Pro 4 doesn't turn on

Hello,
As mentioned I try to use schematics and board view to manage to understand what happens with my surface pro 4 motherboard.
According schematic page 8, I have to find 3.3 vsb and 5 vsb which to be presents on standby.
With boardview, I manage to find points on motherboard to mesaure this 2 voltages.
For 3.3 volts VSB I found 1.5 volts and 0 volts for 5 volts VSB.
I think with my limited knowledge to solve this problem first.
What do you think . It's a good start ?
Have you some clue to find culprit of this low 3.3 VSB and lack of 5 VSB ?

Best regards, Nicolas

[youpla]

Re: Surface Pro 4 doesn't turn on

No 1.8 Volts VSB either.
I test standby voltages with charger only, no battery connected. I don't no if it's an important observation but I want to clarify

[youpla]

Re: Surface Pro 4 doesn't turn on

All VSB voltages must be present on standby ?

[youpla]

Re: Surface Pro 4 doesn't turn on

I also try to find some clues by using page 5 of schematics. This page deals with power sequence. I focus on first steps.
According this page, voltages of always_on and 3P3VA_EN go to an step-down converter which produce differents voltages. I could see it on first attachment.

With help of ifixit teardown, I think that I localised an step down converter. Values seem be good except 3P3VA_FB and 3P3VA_SLEEP. You could see values on second attachment.

Am I not be able to localise step down converter for 1.8 volts and 5 volts. Could you help me ?

Best regards, Nicolas

[reformatt]

Re: Surface Pro 4 doesn't turn on

Follow the numbers on Pg5. The EC (which you have replaced) is responsible for most of the enables for the S5 power supplies, however this does require some feedback from the PCH in order to output the enable.

For example, EC outputs PCH_DPWROK (6), which then requires SLP_SUS# (7), in order to then output VSUS_ON (8). Only with that enable will you see +3P3VSB etc turn on.

You have to start at the beginning and work your way through, this is why the power sequence diagram is a good troubleshooting tool. At the very least, you need +3PV3_EC @3.3V and EC_RST# high. If the latter line is 0V, then the EC is stuck in reset and won't do anything. Additionally, the EC has to load its code from the EEPROM U3104 on initial power on/reset. You need a scope to see if there is indeed any activity on the data lines and that's also assuming the code therein is ok.

[youpla]

Re: Surface Pro 4 doesn't turn on

Hi reformatt,

I just check +3PV3_EC and I found 3.27 volts which is good and for EC_RST# (called I guess EC_RST_ in boardview) I found 3.14 volts which is high value I guess.
I don't have a scope to test data lines of EEPROM of IT8528G.
I only own an multimeter.
I will try to follow step of power sequence diagramm.
Thanks a lot for your help.

Best regards, Nicolas

[youpla]

Re: Surface Pro 4 doesn't turn on

If I understand, at step 5 I have to find voltage for VCCDSW_EN. With boardview I found an point to meseaure this voltage which is 0 volts on my board.
According you, what value I have to find ?

An stupid question but what is meaning of EC after voltage value ? Same question for VSB ?

Best regards, Nicolas

[reformatt]

Re: Surface Pro 4 doesn't turn on

The hash tag (#) for a logic line indicates it's active low. VCCDSW_EN is thus active high so 0V isn't correct. It's early in the power sequence so this is likely an EC issue. Reflash the EEPROM with known working EC code from another unit to rule it out.

[youpla]

Re: Surface Pro 4 doesn't turn on

Hi reformatt,

Thanks a lot for your help.
Unfortunately I don't own a flash eeprom writer in order to flash eeprom of it8528vg.
Just an question for you. What do you think about voltage of 1.54 v on coil near USB port. According board view I was expected to find 3.3 volts. And what about 3 ohms to ground found on coil from cpu power rail. You could find all measurements I talking about on my first attachment.
And finally my last question for today. What means VSB after a voltage name.

Best regards, Nicolas

[youpla]

Re: Surface Pro 4 doesn't turn on

I watched somes videos and it appears that when main board is just connected to charger (without battery) which is my case, I have to find 3.3 volts and 5 volts on coil on the left of PCB near USB port (see attachment).
Someone can confirm ?
If true, TPS51385A could be defective ? It's an driver for 3.3 volts and 5 volts FET if my understanding is good ?

[youpla]

Re: Surface Pro 4 doesn't turn on

I puted battery back in case of VCCDSW_EN will appear unfortunatly it isn't the case.

Maybe I resoldered the chip it8528vg wrong.
However I find the voltage 3V_EC. Is this a reliable indication that I have soldered the chip correctly?

I'm afraid it's game over for this motherboard

[reformatt]

Re: Surface Pro 4 doesn't turn on

+3PV3_EC is an input voltage to the embedded controller, it does not produce it. The reason you see it absent in some websites is that the EC was likely shorted in those cases. It is wrongly listed as a PMIC, as there are no public datasheets available for that IC. However since we now have a schematic, you can clearly see it is an embedded controller.

You should also take note, that an enable might only be present for a few seconds after power on. The EC will typically provide an enable for a power rail, and it will only proceed to the next step if it gets a power good signal for that rail. So something to check for what activity you get after power on.

[youpla]

Re: Surface Pro 4 doesn't turn on

Something change on my surface pro 4 motherboard.
Last evening I decided to let charge battery during all night long to carry on my tests using battery.
This morning I notice battery is flat whereas voltage was about 7.5 volts before I put battery in charge.
Now I have only 2 volts on big coil and 0 volts on output mofset near charging port.
I have 2.45 volts on coil from 3.3 volts rail and 0.62 volts on coli from 5.5 volts rail (near USB port).
I can't figure what happens....
Could you give me some help or give me some measures to do to highlight root cause of this sitaution ?

[youpla]

Re: Surface Pro 4 doesn't turn on

I managed to retrieve my first situation by replacing another time the IT8520G. As before I have an fluctuating voltage (between 7.5 volts and 8.69 volts) on the big inductor mark with an red rectangle on the first picture when power adapter is plug in. Someone can tell me if this fluctuating voltage is normal ?
I noticed that this fluctuating voltage is also present on mofset near power adpater connector (picture 2). If I am not wrong, according boardview, gate pin on the left mofset is connected to the third pin of an 6 pin labelled "DP". Voltage on this third pin is fluctuating too (between 0 and 6,8 volts). I wonder if it's normal or if this behaviour could be culprit ?

I also noticed that the battery discharge completely after 3 or 4 days.

Best reagrds, Nicolas

[regged]

Re: Surface Pro 4 doesn't turn on

Does someone flash it8528vg here?