Mount eMMC after booting from SD card

[User 11436]

You can, but it involved having the back plate off. There might be another way to do this, but  what you'd want to do is :

Insert your bootable SD in the PBP.

Open the lid and lay they palm rest down on a surface, with the lid hanging off the edge. (recommended to avoid flexing/breaking plastics.)

With the emmc switch off, turn on the PBP.

When you see the power LED activate (uboot from the SD has started) turn the emmc switch to ON. You should have a few seconds from turning on to do this.

The PBP should now boot using the SD, with the emmc initialized by uboot. From there, let it boot up and do the maintenance you need.

Thanks for your help.

I managed to boot into my SD with the eMMC visible. Unfortunately, I wasn't able to undo whatever it was I did to uboot on the eMMC, so I'm reinstalling Manjaro.