No PWM coming from mosfet controllers

Xbox Series Questions Xbox Series X
1

Hello. I got in an xbox series x that was taken apart to clean, then reassembled, after that, it powers on then off instantly.

So far, I have found that the connector from the SOC board to the SB board is complete and no faults there.

I have found that the two ic’s that control voltage to the memory, soc, cpu and gpu DO recieve an EN signal, and probing the pwm outputs (that go to the intellegent mosfetss) of both of the ic’s go high, but there is no PWMing (probed with oscilloscope).

So the EN pin goes high, the PWM output (all of them) goes high for about half a second, then everything goes low again.

I have inspected the boards both sides with a lense, three times already, there are no missing components, and no missing standby voltages. The power on sequence of the xbox one was the memory first, then the nb core, then the cgpu. This one seems to be all that together, as the same enable line goes to both the controllers.

What could cause there to be no pwm signals going out to the mosfets? I do get a really low ohm reading on the gpu side (0.1ohm), but even if that was a real short, there should still be some PWM to try to turn it on, but it just goes high and that’s it.

Any advice?

2

Here is a snip of the schematic of the memory mosfet controller. I can’t see why it would be “waiting” to start the pwm if it has an EN signal, and the PWM lines go high.

memcontroller
memcontroller1498×834 174 KB

3

I know both the controllers have I2C communication with what I am assuming is the southbridge. So maybe there are checks being done, and the southbridge “tells” them not to start PWM, but this is an assumption. On previous generations, the MEMIO and MEMPHY would at leat pulse a couple times even if there was a dead short, same goes for NB. So I would assume that these should at least pulse once to determine if there is a fault, but I don’t see any pulses at all, on any of the lines.

Can anyone tell me what gfx core resistance to ground is? My 0.1ohms seems very low, but I have seen graphics cards with extremely low resistance still work.