Microsoft Surface Pro 4 - Intermittent short on 3P3VA

[Prott]

Hello,
I am recently stuck with a weird fault on M$ Surface Pro 4. There's a short on the +3P3VA phase that prevents the tablet from turning on. But when I try to inject voltage the short goes away (the more voltage I inject the quicker it goes away - if I inject 1 V it takes few seconds, if I inject 3 V it goes out immediately).

This way (after reassembly) the tablet works as normal for some amount of time until the short appears again (after 1-2 weeks of non use).

It is very hard to diagnose which component could be faulty because of the fact that I can't inject any voltage to see what gets hot. :/

Did anybody encounter similar problem? Thank you so much

So far I measured following:
1. The short is on +3P3VA line, not on any line connected to it (tried by removing components to narrow it down).
2. It's not (fortunately) caused by U3102 (the sensor MCU).
3. I replaced the hall sensor (U3204) as well as the 1.8V regulator (U5505).
4. I can't easily get to the U3206 chip (as well as its other supporting circuitry) that's under a soldered shield and a conformal coating. Not sure what the chip is for (Artalon?) and if it's worth to dig to get to it. Would prefer to try any other option first

[ahmypc]

Re: Microsoft Surface Pro 4 - Intermittent short on 3P3VA

You have to look at the last place you said you would deal with. The source of the problem is U3206 or U3207 . Maybe both together. Remove the coating, first heat the IC and vibrate it. If there is still a short circuit, remove the integrated completely and check the 3v and 5v capacitors around it.

[Prott]

Re: Microsoft Surface Pro 4 - Intermittent short on 3P3VA

Thank you so much for the advice and a picture. I will carefully do that then.

Also I discovered a new problem - I am getting an error 14 on the touch firmware. The touch portion of the screen is not working (both in windows and in the UEFI). I checked all the resistors that connect the port and CPU (SPI lines) as well as voltages. Resistors are fine (either 0 ohm, 15 ohm or 49.9k ohm as per the schematic) and voltages (1.8 and 5 V) are present. I also tried two separate touch boards, but both behave the same.

Not sure if that problem could be in any way related to the first one. :/

[ahmypc]

Re: Microsoft Surface Pro 4 - Intermittent short on 3P3VA

During the heat treatment, the soldering feet of the glass integrals may deteriorate. It may be necessary to check the elements around the connector and below. Also, the touch issue may be software related. The problem I'm dealing with the most is the touch problems that occur after the firmware update.

In addition, the U3105 IC may be affected by a short circuit in the 3V path.

[Prott]

Re: Microsoft Surface Pro 4 - Intermittent short on 3P3VA

Thank you so much! Yep, fixed the short - now the resistance from 3V to ground is in the range of kOhms. However I moved a lot of components under the metal shield when I was removing it. Spent a good few hours resoldering everything back in place

Now I have to wait for one of the regulators to arrives through mail, because during the soldering it flew away into another dimension. :/ After that I will reassemble everything and test it. Hopefully everything else made a good contact and will work.

Thanks again!

[ahmypc]

Re: Microsoft Surface Pro 4 - Intermittent short on 3P3VA

I forgot to write, use a pump when removing the metal plating.

[Prott]

Re: Microsoft Surface Pro 4 - Intermittent short on 3P3VA

yeah... I wish I thought about it a bit more before doing the same mistake. TWICE First time wasn't too bad, so I was like: "for sure I can do better now". Nope, I obliterated almost all the components.

[Prott]

Re: Microsoft Surface Pro 4 - Intermittent short on 3P3VA

Ok, the short seems to be gone (still a few kOhms of resistance to gnd, even days later). Though the one problem remains - no touch and touch firmware error code 14.

I am trying to update Windows in chance that it will also update the touch FW. Will update.

Thanks again!

[Prott]

Re: Microsoft Surface Pro 4 - Intermittent short on 3P3VA

FIXED: ahmypc's advice was spot on.

Touch FW error 14 was caused by a knocked off 0 ohm resistor (PR6547).