The guide has been fixed.

The guide has been updated.

This usually occurs when you break the lower screen's power ribbon cable connector. It is not a ZIF connector and "unlatching" it will break it causing a loose fit. The shoulder button presses against the ribbon cable causing it to shift in the connector resulting in the speakers popping and the device turning off.

Guide has been updated.

I made the same mistake. The guide is now updated.

Not ideal, but you can use replacements for DSi and (not-new) 2DS which are very common. This worked for me. They seemed identical except for 2 features:

1. New 2DS has a single centered leg in the front. DSi has two in the front on the sides.

2. New 2DS has plastic on the bottom that sets it about 1mm off the PCB. DSi does not.

You have to remove the extra 2 front legs (don't simply bend them inward, this blocks cable insertion) and use something as a spacer to prop it off the PCB about 1mm. I used thin cardboard. You can compare it to the existing port before you remove it. Worked like a charm for me.