Help disabling a vcore phase on a MSI X570 Carbon - I have schematics + boardview

[SavaBogdan]

Hello.
Does anyone have any experience with disabling a power phase on the CPU vrm?
The controller is IR35201 6+2 phases. It only uses 5 phases and the pins for pwm and feedback on the 6'th phase are not populated (no traces).
I got the board with a burned mosfet which I removed along with a part of the pcb. I dremelled away the short as best I could and the board started up fine without the vrm heatsink.
I then put some sealant and left it for two days to completely dry. I suspect the pressure from the thermal pads on the heatsink compressed the layers so when I started it with the heatsink installed i got sparks from that area.
I opened it up again and had to grind away another part of the pcb including the second mosfet from the 5'th phase. The board uses doublers.
Now I get +1.0v for a second at startup and then it disables the vrm. I don't think it likes both dual mosfets removed from the doubler.
The pwm is ir35201, the doublers are ir3598 and the dual mosfets are qa3111
I read that some controllers don't like it when you remove random phases, you can only disable them from the last one going backwards, but mine is already nr 5.
I saw in the datasheet that you have to short to ground isense and ireturn pins on the controller when the specific phase is not used but the pins for pwm isen and irtn on the 6'th phase don't go anywhere and are not grounded.

I am attaching schematics and a boardview for this exact motherboard.
Boardview was a little hard to get but I managed it.
Thank you

[Monkeyballs]

Re: Help disabling a vcore phase on a MSI X570 Carbon - I have schematics + boardview

I don't get it ?
U6 is unconnected right ?
If only U5 is connected but broken VCC_NB is not generated.
Choke 6&7 responsible for it

[SavaBogdan]

Re: Help disabling a vcore phase on a MSI X570 Carbon - I have schematics + boardview

Hi. I was referring to the pwm pins on the ir35201 controller.
From factory they use:
1->5 pwm pins for vcore - used with ir3598 doublers to make up 10 phases
chokes 15 14 13 12 10 9 2 3 4 5 - weird numbering but that is the order

6 pwm pin is unused

7 and 8 pwm pins (the +2 phases, second loop) used with the same ir3598 but set up as dual that drives two dual mosfets
choke 6 and 7

[SavaBogdan]

Re: Help disabling a vcore phase on a MSI X570 Carbon - I have schematics + boardview

At first i found the mosfet connected to choke 4 burned and welded to the board. I had to grind away the short and the board started up.

After I installed the heatsink and messed up more of the board (pressure caused another short) I had to grind away and also remove the mosfet connected to choke 5.
From that moment I no longer had vcore

The +2 phases that power the SOC are working (choke 6 and 7)

I read the datasheet that said to ground isen and irtn and float pwm pin, this way the controller automatically disables the phase and runs as a 4 phase.

I removed the doubler so the 5th pwm pin is floating, i removed the caps and resistors from the 5'th phase feedback near the controller and also cut the traces (cp21 and cp20) that went to vcore for monitoring. I also grounded the pins.

Still it does not want to turn on vcore. I checked all the feedback circuitry, all the traces from controller to doublers, all enable pins on the controller and all are ok.

I am thinking something else died when I powered on the board and it shorted but I don't know what that could be.

I have been measuring and stabbing the board for two days now, maybe I am getting tunnel vision and missing something obvious