Xbox One X 3.3v Short

[ajp8868]

Hi All,

Looking for some help/advice on trying to fix an Xbox one X motherboard which seems to have a 3.3v short to ground. The symptoms are quite common, it turns on for a second then goes off instantly.

I've checked a number of points on the board and it seems there may be a short somewhere but locating that seems to be very difficult. Does anybody have any advice on how to locate a short without removing every component it could be?

I'm also looking to see if anybody could identify this component attached
as I've broken it when removing (my hot air station doesn't seem to be hot enough)... The only marking on it is GEH which I can't find any info for!

Many thanks!

[fzabkar]

AP2127-ADJTRG1, Diodes Inc, 300mA, 2.5V - 6Vin, HIGH SPEED, EXTREMELY LOW NOISE CMOS LDO REGULATOR, marking GEH, SOT-23-5:
https://www.diodes.com/assets/Datasheets/AP2127.pdf

[ajp8868]

Ah brilliant thank you! Don't suppose you have any advice as to why these are so hard to remove with a hot air rework station? Can't seem to melt the solder..

[TheMG]

It's probably sitting on large power/ground planes in the inner layers of the PCB, through all those vias.

Pre-heating the PCB can help a lot by reducing how much heat is being sucked in to those planes.

[ajp8868]

Makes sense, thank you for the advice.

Sorry to ask so much but do you have any advice on what components to check first for a short to ground? I've checked some MOSFETs and voltage regulators which seem to be behaving normally and when removed the short is still there.

Is it likely that it could be one of the tiny smd capacitors between ground and the 3.3v rail or do these very rarely cause issues?

[TheMG]

The technique I use to find a shorted component on a rail that has a lot of components on it is to carefully apply current from a bench power supply to the rail. Start low and see if any component gets warm. If nothing then give it a little bit more current, keep going and eventually the offending component will usually start to heat up as long as it's not a total dead short (much less than 0.1 ohms).

It help to have an IR camera but obviously not something everyone can afford. I use my fingers or some isopropyl alcohol on a cotton swab. The alcohol will evaporate noticeably quicker from a hot component.

[ajp8868]

Thanks so much TheMG, found the location of the short (sort of)

It seems that the whole area around the chip in picture 1 is heating up.. could it be this chip or components around it?

I've pictured the other side of the board too where it heats up, wondering if it might be another layer at fault?

[ajp8868]

Other side of the board (images are too large)

[fzabkar]

Have you checked whether any of the ceramic capacitors are warming up? They are a common problem.

This is the datasheet for the MP2853:

https://www.monolithicpower.cn/cn/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP2853/

[ajp8868]

It's quite hard to tell as the whole area seems to get warm, think I might need to get hold of a thermal camera.. anybody in the Teesside area hiring them out? 

I guess the easiest thing to do from this point would be to de-solder a few?

Thanks for the datasheet, that's some light reading for later lol

[fzabkar]

I've never used one, but what about an IR thermometer?

https://www.drivestar.biz/index.php?main_page=product_info&products_id=1038&zenid=v2dch9v76so2ef637gb827cv84

[ajp8868]

I think my work has one I might be able to borrow actually. Will give it a go!

There's no real way to test these caps without removing is there?

[fzabkar]

I always end up removing any suspect caps, but there are probably techs who know a better way.

[ajp8868]

Just waiting on some flux to see if I can actually remove anything so will try again tomorrow and see if I get anywhere. Thanks again!

[langwadt]

It's quite hard to tell as the whole area seems to get warm, think I might need to get hold of a thermal camera.. anybody in the Teesside area hiring them out? 

I guess the easiest thing to do from this point would be to de-solder a few?

Thanks for the datasheet, that's some light reading for later lol

the Luis Rossmann trick is to pour on some alcohol and see where it evaporates first

[TheMG]

That IC, MP2853, is a voltage regulator controller for the switching regulators presumably providing power to the CPU. The chip itself doesn't handle much power, it's just a controller for the actual switching regulator ICs.

Per the datasheet, this IC appears to have a ground pad underneath that's soldered to the ground plane of the PCB, that's probably why the whole area is heating up.

https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP2853/document_id/6613/

Any other ICs or transistors in the vicinity also getting warm?

[ajp8868]

Well I can't feel anything specific heating up. But I've noticed that when I put positive lead on the point circled in blue the CPU heats up, where as when I put voltage to the point circled in red, that other area around that other chip heats up.

Could it be a CPU issue?

[TheMG]

The point circled in blue I don't think is on the 3.3V rail, that looks like the output of the switching regulators going to the GPU chip, which is normally going to be much less than 3.3V (usually in the range of 1-2V).

[ajp8868]

Oh really? In that case it seems there's a short on that rail too, and it's the graphics chip that gets hot.. would that mean it's quite likely the GPU is knackered or at least shorted?

[grumpydoc]

Inject a low voltage - max 1.0V into the 3.3V rail from a current limited PSU then

- see what gets hot, pay particular attention to ceramic caps

- try Rossmann's alcohol trick

- probe the 3.3V rail starting at the PSU, as you work towards the short the voltage will drop (really need at least a 20,000 count DMM), if the voltage stops dropping you are moving away from the short.

- if you can get hold of a thermal camera by all means try to see if you can identify the hotspot.

[ajp8868]

Thanks for that, really tried to narrow it down with all 3 techniques but so far all I see is that chip and the area surrounding it getting hot.

 I don't think my MM is good enough to detect the tiny voltages you're referring to but as far as I can tell it's getting to 0.1 near that chip and that's the lowest reference voltage.

I was going to try removing it to find out if the short was fixed but I cannot for the life of me remove anything with hot air, doesn't even seem to make the solder soft. Do I need flux paste?

[cheeseit]

Which hot air station is it and what temperature is it set to?

[ajp8868]

It's a WEP 853D and I've tried it on all sorts of temperatures right up to (what it says is) 896c. Heated up the whole board first too but nothing comes off..

[cheeseit]

It's secondary to your problem with the Xbox but it's critical for fixing it. Something must be wrong with that hot air station, it should be able to melt the solder. Do you have a suitable thermocouple for your MM? If so, check the temperature of the hot air. If not, see if you can get hold of that IR thermometer or buy one, they cost next to nothing.

Check a few videos on using hot air, just to see if you've got the technique down and don't cook the board in the process.

[ajp8868]

Just bought an IR thermometer, it'll come in handy more than once I bet. The gun does get very hot so I'm surprised it's not melting the solder, seems like I might end up having to fix that first 

So I've been doing a little more investigation on the parts that are shorted and it seems that nothing around the AP2127 chip is shorted. However, everything on the left hand side of the chip, towards the CPU is shorted to ground. Is it likely that the CPU is fried?

I've also come across a component labelled FB2 which looks a little damaged, does anybody know what this is?