Hardware What's the function of the MAX67721 next to the SD FPC?

[tomsek68]

Hi everyone!

Recently i had to open my switch, because it froze. (i was trying to load shofel2)
None of the reset methods worked, and the battery was on full charge... So i decided to open it.
Everything went fine after reconnecting the battery (it was booting once again to OFW).
I noticed that one of the pins were missing from the SD FPC, and sure it wouldn't read cards. The missing pin was stuck on the slot's connector, so i soldered it back in place.

After cleaning the solder paste, it was booting to CFW. After a few minutes, it went black. I learned that my new solder paste is conductive, and it was stuck under the nearest buck converter. The chemical reaction ate away the pads on the IC. Without the IC, it shows Nintendo logo, boots into payloads etc.

So...
What does the MAX77621 buck converter supply which is near the SD FPC? The GPU?

 

[tomsek68]

Can anybody measure the voltage on the 3 phases during boot? Does anybody know anything about the pinout?

 

[SheriffBuck]

Can anybody measure the voltage on the 3 phases during boot? Does anybody know anything about the pinout?

There are a pair of the MAX77621 subsystems one feeding CPU and the other GPU.

I can get you some measurements tomorrow if you still need them?

Sheriff

Sent from my SM-G975F using Tapatalk

 

[SheriffBuck]

So the MAX77621 buck closest to the USB-C is for the CPU. It comes on almost immediately after the bootstrap processor hands over to the main core on boot. I measure about 0.8v (there are two convenient square test pads to the left).

The second buck near the NAND drives the GPU and doesn't fire up until later in the boot cycle. Again, there are 2 square test pads below where you can measure 0.8v.

When the screen turns off, the GPU power shuts down immediately. The CPU power shuts down after approx 30 secs.

Neither of these fire up until after a payload is injected with RCM.

Sheriff