Xbox One won't boot, missing 5v on standby?

[technomancer]

Hello,
I’m taking a look at an Xbox one for a friend that won’t power on. The power supply brick is outputting 5v and, after coming across the standby voltages image, I started probing around to see what may be missing. I noticed that, at a minimum, I am missing 5v to some parts of the board. I think I have narrowed it down to something being bad in with U4B4. There are 4 pins on one side of the component that are supposed to be getting 5v (I marked U4B4 in the link) which aren’t, and after that the 4 resistors above it are supposed to be getting 5v. However, on the other side of U4B4, the second pin from the right is supposed to be getting 5v, which it is, but so is the pin on the far right which is not marked as something that is supposed to have 5v in the diagram (to be fair it isn’t marked at all).

 

What exactly is U4B4 and should that pin on bottom right also be getting 5v?

 

On the component itself it reads:
4501B
SAT▲ (the ‘S’ looks more like a symbol of overlapping S’s and the delta triangle is hollow)
.W43C

 

Link to the part of the standby voltages page with U4B4 marked:
Link to the standby voltages page: https://obrazki.elektroda.pl/3805336400_1496318649.jpg

Edited October 25, 2021 by technomancer

[technomancer]

I got the info on what U4B4 was from a kind soul on another forum. It's an Si4501BDY-T1-GE3 (data sheet hyperlinked). I tried replacing that chip with a new one but it didn't seem to help at all. I am really at a bit of a loss here. I compared the unit another working Xbox One (with a slightly different board) and got the same voltage measurements on the source/gate side of the chip as I do with the broken unit. I just have no idea what is preventing voltage from going across that chip to drain. Below are a couple of pictures I took with voltage measurements:

 

Working Xbox One: https://imagizer.imageshack.com/img923/2958/kuHYlc.jpg

 

Broken Xbox One:

 

Any help you could offer would be greatly appreciated.

 

[PCFI]

I know this is an old post but I worked on an Xbox that was also missing its 5 volts standby but it turned out, it stemmed from me missing the 3.3 volts.  There are two MOSFETS, U4B4 and U3C1.  U3C1 should have 5 volts on the drain to supply voltage into U3C2 which creates your 3.3 volts standby.  Without the 3.3 volts standby, I could never get 5 volts on the drain of U4B4. 

 

U3C1 is controlled by U7P1 which is a dual PNP chip.  Pin 5 is the base (around 2.8 V), pin 4 is emitter (tied to ground), and pin 3 is the collector (this controls the voltage on the gate of U3C1). If you are missing the 5V on the drain of U3C1, you can lift gate leg of the chip or you can short pins 3 and 4 of U7P1 forcing ground on the gate of U3C1, which will cause it to conduct.

 

Once I did this, the power supply kicked in and the console booted.  I made a video about it if you care to search Youtube.

 

Not sure if this is your problem but it may be worth a check.

[+wongojack]

I now have an XBox One that will not power on.  I suppose this info could be helpful, but I will probably just upgrade.  In a way, it is kinda sad that the reasons to keep the XBox One going are kind of limited especially if you can afford to replace it.

 

I may still try to open it up and fix it.

On 2/7/2022 at 3:35 PM, PCFI said:

I know this is an old post but I worked on an Xbox that was also missing its 5 volts standby but it turned out, it stemmed from me missing the 3.3 volts.  There are two MOSFETS, U4B4 and U3C1.  U3C1 should have 5 volts on the drain to supply voltage into U3C2 which creates your 3.3 volts standby.  Without the 3.3 volts standby, I could never get 5 volts on the drain of U4B4. 

 

U3C1 is controlled by U7P1 which is a dual PNP chip.  Pin 5 is the base (around 2.8 V), pin 4 is emitter (tied to ground), and pin 3 is the collector (this controls the voltage on the gate of U3C1). If you are missing the 5V on the drain of U3C1, you can lift gate leg of the chip or you can short pins 3 and 4 of U7P1 forcing ground on the gate of U3C1, which will cause it to conduct.

 

Once I did this, the power supply kicked in and the console booted.  I made a video about it if you care to search Youtube.

 

Not sure if this is your problem but it may be worth a check.

I'm looking for the video.  Do you have a link?  I don't suppose you have a photo of U7P1 - and could you tell me if you left the XBox in that state or did you eventually replace the PNP?  Was there a permanent fix?