One x, shorts around APU (0.000v voltage drop)

need a little bit of confirmation here. Xbox one X, shorts around APU (dead shorts, not low resistance). Is this APU shorted or can there be something else causing these shorts? Can someone confirm what is the resistance to ground at V_cpucore and V_gfxcore test points. The board is cactus M1037358-004. Thanks!

I tried voltage injection at 1V/1A but don’t get any heat signatures on the board, not even 1 celsius increase in APU. I’m pretty sure this is the highest safe voltage around vcore lines.

Hey sorry I’m not going to be able to help with direct measurments as I don’t have a one X board to compare with

But just to confirm, am I correct in thinking that everything you’ve circle in yellow is equal to diode 0.4V? and everything circled in red is a dead short? as if that’s the case then it does seem like all your shorts are stemming from the APU side of things with the output inductors removed :frowning:

Instead of measuring in diode mode, can you measure in resistance and overlay that on your image instead?

Also I don’t typically work on xbox consoles but I guess the primary voltage from the PSU is 12V? and maybe a 5V rail too? it might be a good idea to also measure the resistance to ground of these rail/s also

Thanks!

Yes, there are at least one line shorting (gfx, 4 phases?)

resistance To ground values (black on ground)

12v line ~ 50k ohms
5v line ~ 30k ohms
3v line ~ 1k ohms

That’s unfortunate as it seems to be the short to ground/s are directly in line of the APU/GFX phases, looking online these rails would normally measure somewhere in the 8 ohm region afaict so it’s very likely the APU which is the problem :frowning:

I think it would be unlikely a fault on one of the ram ICs would drag down the other rails, but not impossible I suppose I guess they’ll be on an independent 1V8 rail and an approx 1.2V rail (guessing) so it might be worth measuring the resistance of a few of the bypass caps surrounding the ram IC/s to get an idea f they’re at fault or being dragged down much like te CPU rail currently is

Thanks! I have also removed the diodes from the rails below the board to rule them out (two black ones on the picture)

I’ve checked the RAM capacitors too, most of them are 12 ohms, which is normal AFAIK

Looking at images of the board, there seems to be at least two ICs which are responsible for phase regulation for the APU, and I’m guessing again here, but would imagine one IC is responsible for GPU rails and the other CPU rails… maybe Ram regulation is taken care of by one of these also… or maybe the primary/secondary ram rail is sharing the rail/s with the GPU rail/s (for example)

Afaict by removing the inductors you would rule out U57 as the possible fault (again this is a complete guess)

The other, U64 I’m not so sure about, whether it’s now isolated or not from the APU (?)

I checked the components around U57 and U64.

U57 has some low resistance resistors (~3 ohms).
And U64 has DB408 (3 ohms) and resistor R589 (gives 0 ohms), it looks like it’s connected to the IC’s ground (corner of the chip).

What’s the resistance to ground on L17 ?

btw what was the suspected cause of the failure? is this a liquid situation or drop, or initially an HDMI issue etc?

Some mega ohms.

Owner said the first issue was disappearing screen and after two weeks it wouldn’t turn on anymore. When I pretested it, nothing happened when I pressed the ON button (or controller xbox button). The PSU supplied 12V.

The HDMI port is fine

I see, I think it’s very unlikely but I’d probably pull the HDMI Redriver IC as a matter of course, though can’t see how a fault on that would pull the GPU rails low…

I reckon it’s probably the APU in this case unfortunately as symptoms of “disappearing screen” fits with the current GPU fault, but I suppose you could pull the phase regulators - on the off chance they’re responsible and then all the ram… but again I don’t think these are likely to be causing your shorts.

I think this xbox has also faulty HDMI redriver, I have documented the diode values and diode value of C25 next to the HDMI booster IC always reveals if the redriver is faulty. But it cannot cause the shorts on the APU.

I appreciate all the help. I have to declare this to be a no fix… :frowning: