Xbox one s dead only 12v no 5v etc

[Dean3083]

Hi everyone, having a bit of trouble finding the fault on a Xbox one s was hoping a standard shirt on the 12v line mosfets but nope all ok I checked what I believe is everything it came to me with a dodgy hdmi port removed that and the retimer chip I checked the voltage rails have 12v in and out but no 5v or 3.3 1.8 etc all dead. I checked the mp8757 I have 12v in and 5v on 2 of the pins and a 2v on en but no 5v output line removed coil to see if being shorted after but still nothing anyone else have any situation the same as me. I’m assuming without 5v I’m not going the get the other lower voltages.
Tia dean

[MathWizard]

Do you have an oscilloscope to see if the 5V tries to reach 5V ? IDK about consoles, but I'm guessing the start up on a routine, and when each stage is ok, it signal's the next stage to start up.

Maybe it's that chip
https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP8757/document_id/905

Have a good look at the little circuit around it. They call the enable pin a digital pin, I see it mention 2V. But maybe there's a lot of noise on it too ?

Maybe the output caps are going, and it can't raise the output enough, and shuts down ? Again a scope would be useful.

[Dean3083]

Hey sorry late reply life got in the way as always.
I have diy mini oscilloscope I did a brief check and no 5v whatsoever I removed a few caps in case pulling to ground no change I have 5v on to other legs I sent to 5v out it was stable couple milliamps that in turn powered my 1.8v and 3.3 and finally the power button reacts. I’m going to assume I need a new mp8757 as also assuming my 2v engage is high enough.

[tom66]

MP8757 requires at most 1.35V on the enable pin to turn on.  You can find this figure in the datasheet:
https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP8757/

under parameter "VILen" (page 4).

So I agree with your conclusion, provided you have eliminated the possibility of a short circuit on the output side of MP8757. (Check with a multimeter across the caps for a short using the ohm setting.)