Nintendo Switch Oled HEG-001: Second-Stage Boot Failure

[imperialboard89]

Hello everyone,

I'm facing an issue with a HEG-001 motherboard that is unable to complete the Second-Stage Boot. I'd like to start directly with my conclusion, which is the decision to replace the MAX77621AEWI chip, and understand if it could be a correct evaluation.

Before I dive into the process that led me to this decision, I want to mention that I have a fully equipped lab where I can perform any kind of tests.

Let's begin:

Following some guides online, I tried to understand how the Boot phase of the Nintendo Switch works, and what are the important components for the console's startup.

First, I checked for a short circuit on the inductor of the VSYS line (4.2V). Once confirmed that there was no short on that line, to analyze all the components involved in the First-Stage Boot, I started by powering that line with 4.2V, and the bench power supply showed an absorption of 0.2A, indicating that the First Boot phase was occurring correctly.
Then, I went to check if all the voltages related to the First-Boot and the First+Second Boot were present (

) and they were all present. However, the V8, V11, V12, V13 voltages were missing.
Since from what I understand: the Second Boot phase is divided between two identical chips (MAX77621AEWI-1 and MAX77621AEWI-2) which also share an identical circuit, so if one of the two chips does not work, the Second Boot phase should not start; based on this reasoning, I went on to inject 1V and 1A into the circuit of the chip MAX77621AEWI-1 but I did not notice any current absorption nor heating by the chip or any component. I also tested the circuit components in diode mode but there was no short circuit.
I performed the same test by injecting 1V and 1A into the circuit of the twin chip, i.e., MAX77621AEWI-2, and I noticed that indeed the chip made the isopropyl alcohol evaporate. I checked for a short on the components that were part of the circuit and the multimeter (in diode mode) marked a short but not at 0V, rather at 0.063V (which made me assume it was a false short circuit). After removing the chip, I noticed that the 0.063V value on those components was still present. The strange thing was that I couldn't identify the heating of the chip either through a Thermal Camera or with Rosin, but only with the evaporation of the alcohol. So, I had the doubt that the chip did not heat up enough to be detected with a thermal camera or with rosin.

The question I now ask you is the following: Could it be that, even if the chip did not heat up enough during the injection phase, is it still the culprit for the failure to start the Second-Stage Boot?

In any case, I have already ordered the chip and it should arrive in a few weeks, so I have not yet been able to replace it with a new one.

Thank you in advance for the patience you have dedicated to reading this lengthy topic.

[imperialboard89]

After some tests I found out that the issue was a bad eMMC. To check it I connected screen flat, backlight flat, battery and usb-c cable between board and pc. Then I opened RCM Tegra software and it detected that the console was in RCM mode, this means the board can't read the eMMC, like when you put the console in RCM mode. Other than that the board works perfectly. As I understand it, the eMMC is irreplaceable, so the card is unusable. Or is there a way to recover it even without backup?