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**mcplslg123** · 03-16-2023, 08:16 AM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

This cant be a bios issue for sure. Seems like dc-in mosfet is leaky though not shorted.

**Prott** · 03-17-2023, 11:04 AM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Hey, thank you so much for your help.

The Surface seems to be using TPS65987 controller as the main "mosfet" for USB PD. Can it be the fault of this controller and should I just order a new one and replace it?

I measured the bus coming out of the IC (EXT_DC_IN) against the ground and the resistance is in the range of Kohms and rising. Should I do some more probing to further investigate what's the problem?

Thanks again!

**mcplslg123** · 03-17-2023, 11:02 PM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Is diagram available? If yes attach it.

**mon2** · 03-18-2023, 07:09 AM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Schematics are posted here:

https://www.badcaps.net/forum/showthread.php?t=97151

Check the voltage to ground of VSYS after shutdown event at U6302.

Study the voltage at input and output of the 4 mosfets.

The input is independent and dialed up by the TPS power delivery ic you referenced in the earlier post.

The TPS chip will dial up the 20v or similar power delivery contract from your adapter to power this board. If the adapter voltage is at the basic power up default of 5volt then the TPS chip needs to be reviewed. The firm for the power delivery function is stored inside the external spi flash near the TPS chip.

**Prott** · 03-18-2023, 08:03 AM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Thank you. I made couple of posts, but with each I progressed a bit further in the troubleshooting.

Now the tablet is starting up fine (all the signals are present all the way till PLTRST#, there's even a clock signal from PCH on the BIOS chip). However it only works for a brief moment after which the charger disconnects (resets) and tablet loses power. After that I can try to start it again, but the results are the same (very briefly on, then power goes off due to the reset of the charger).

By the way, I can see the charger resets because I am measuring the power draw with a USB current/voltage monitor. It starts at around 40 mA / 20 V at standby and then quickly ramps up and shuts down completely, indicating a loss of USB power supply.

Is there anything else that I can check or measure? Thanks again

**mon2** · 03-18-2023, 09:06 AM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Can you test with another USB type c power adapter? Perhaps a beefier one with higher current support?

**Prott** · 03-18-2023, 11:42 AM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

It's 65 W one and was working with the whole tablet before (now it's just a bare board). I tested another one just in case with the same result. The current goes up and boom, restart. :/
But thank you for the hunch. I actually didn't really thought before about the possibility that it could be all because of the adapter's flaky behavior.

The board had a corrosion present around the SL connector, which still does not work (even though I removed the corrosion). Both SL and USB PD share the same "EXT_DC_IN" line. Could it be anything related to that problem? Even though I thought it's not a priority at the moment I tried to troubleshoot the SLink problem - it seems as the SLink power doesn't work because of the lack of enable signal to the main mosfet from SAM. That mosfet is used only for SLink and not for USB PD.

**Prott** · 03-20-2023, 06:07 PM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

It's a weird fault. I measured all the rails (as far as I know) that are directly connected to the USB port when the machine is powered on, but so far nothing jumps out to me as being anywhere near shorted (measurements are to ground):

VDD_BATA_PACK: 10+ kOhms, rising
CHG_VSYS: kOhm and rising
VSYS: kOhms and rising

Is it possible that there's a rail downstream that consumes much more power (due to it being shorted) and, in turn, draws THAT MUCH more power through the VSYS rail? I would imagine the buck converter controller for that individual rail would stop converting (or, at least, stop the PG signal) before it comes to that, but I don't have enough experience and knowledge to be sure.

If that's a possibility there's a weird reading on the 1P1V_DDR_VDD2 rail. Only around 6-7 ohms.
All the other rails I measured (VCCIN, 1P1V_SSD, 1P8_VSB, VCC_IN_AUX, VCC_EDB_BKLT, etc.) were all at least 300 ohms in case of CPU and over 1kOhm in others.

**mon2** · 03-20-2023, 08:05 PM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Yes it is possible to have a local rail consume too much current. Remove all power and check the resistance to ground of each coil. The coil will be linked to a switching power rail. Also check linear LDO regulators for the same.

**Prott** · 03-21-2023, 06:22 PM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Thank you, will check them out today and write it all down.

**Prott** · 03-22-2023, 05:36 PM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Here it is

That 6 ohm rail seems a bit out of place there, but I am not sure what is a typical resistance of ground on that phase (nor do I have any other LPDDR4 laptop to check it). What do you think please?

Would rather quadruplecheck before injecting any voltage

Attached Files

**Prott** · 03-25-2023, 11:35 AM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

UPDATE: I put the board through an ultrasonic cleaner - after that I am only getting 5V from the charger. That also appears to point to the fact that the TPS65987 is faulty.

Also, I made a wrong assumption before. If I understand it correctly now the TPS is not doing any voltage conversion. It just connects the 20 V into the EXT_DC_IN bus and the conversion itself is done by the charging chip and couple of mosfets.

**mon2** · 03-25-2023, 12:15 PM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

The TPS65987 is an intelligent, stand alone power delivery controller. It will communicate with the external pd capable adapter to extract the list of power delivery contracts (ie. Voltage & current pairs).

Then this controller will select the best choice from this list of options.

If all is well, this controller will select the 20v power delivery contract.

With 5v being the default out of the power adapter.

**Prott** · 03-26-2023, 04:43 PM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Thank you! So it seems as if the TTPS65987 is having problems? I checked the adapter and it is working with other notebooks / tablets.

Also, I checked with a working board and the 5 ohm resistance on the 1 V memory rail is indeed a problem. It should be around 200-300 ohms. Let's see if I will be able to find the cause with a voltage injection... 5 ohms is still a bit high for that.

**Prott** · 05-03-2023, 03:38 PM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

So, it seems like this failure mode (turning on for a split second and then shutting down immediately due to the restart of the charger) is quite common. Multiple people wrote me since I started this topic with the same problem, asking for a solution. On top of that I came across one other Surface 7 that worked, but after a few weeks started to show similar problems.

I checked both Surfaces and none of them has shorts on any of the rails, resistance is usually above few kOhms for most of the rails (except rails that power ram and cpu, as expected

).

Can anybody please point me to a good direction? I am willing to measure / probe anything.

Thanks

**mon2** · 05-03-2023, 07:26 PM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Review this video and also the comments:

https://youtu.be/gGv5lriyu9w

**Prott** · 05-05-2023, 07:22 AM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Thank you so much for pointing me in the good direction.

I have a problem though - I am unable to locate a valid bios for the Surface. Unfortunately I was stupid and (even though I usually do) I didn't double check the backup copy I made. It turns out it wasn't saved correctly and only has 2 MB instead of 16.

Can you, please, let me know where I can locate a bios that might work or how can I prepare other person's BIOS to work on my Surface?

It seems there are variables (serial number?) in other parts of the BIOS that need to be invalidated before it even has a chance to work. I have experience with cleaning the ME region on SPro 4, but this one is new to me.

Thank you so much. You are saving my bacon big time.

**mon2** · 05-05-2023, 07:41 AM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Hi. Forum is back online

Post your request in the bios section.

**Prott** · 05-05-2023, 08:36 AM

Re: Surface Pro 7 - turning off briefly, then charger cutting off

Thank you! Posted it there

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Surface Pro 7 - turning off briefly, then charger cutting off

Surface Pro 7 - turning off briefly, then charger cutting off

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