Xbox One Original missing 12v enable signal

[tccyo22]

Hi there, I have an Xbox One original in which I have all the 1.8v, 3.3v and 5.0v standby power rails present, however my 12v rail is not turning on and the enable signal PSU_V12P0_EN from the SMC to turn the power supply on is missing. There is high resistance on this line so it's not shorted directly to ground which leaves me with not many options.

Was looking at a schematic and see the enable is created by the SMC. I have 3.3v on SMC_RST_N_IN but I'm a little stuck on where to look next. Is it likely that the SMC has gone bad or am I missing something else (it's my first time with the original xbox motherboard)?

A visual inspection of the board reveals nothing that stands out of the blue and overall looks in fairly good condition aside from a light dust build up as expected.

When I press the power button the white LED comes on for a second before going off, and the light on the PSU is yellow, only goes white for a second when I plug it in and switch it on.

[tccyo22]

Re: Xbox One Original missing 12v enable signal

Update on this, it's not a dead SMC, if i hit the power button enough times I get a spike of 12v on the 12v rail but only for about half a second before it falls back to about 0.6v/0.5v and drains down for a second or 2 before dropping to ~200-300mV. I'm trying to figure out why it gets brought back down. With the speaker plugged in I get the power on sound and sometimes tapping away fast enough also the power down, but most times just the power on sound.

If anyone can share insight on how the 12v enable signal functions, how the SMC should react and what areas I should turn my attention to and double check, I would greatly appreciate it

[stj]

Re: Xbox One Original missing 12v enable signal

probably an overload.
if you have a bench supply you can feed the 12v line with a volt and see how much current it draws.
try not to feed over 1.5v, the lower the better incase a mosfet is shorted on the cpu supply.

[tccyo22]

Re: Xbox One Original missing 12v enable signal

The mosfets around the CPU were the first thing I checked and the diode readings all read the same as a working board so I don't think injecting voltage is going to reveal anything.

I think I might try replacing either U9F3 or U9C2 (or both) and see if that helps. I don't have a schematic or boardview for this specific board so I'm not sure where to find the PWRGOOD signals to check

[miyagik]

Re: Xbox One Original missing 12v enable signal

Any updates ?
Having a similar problem