SD card not found, but OK on USB power

Helping a guy out. Odd behaving board.
With USB connected, all is well with or without battery power.
When USB disconnects (batt still engaged) the saber turns off. At this point, pressing power gives “Font directory not found.” EDIT with non-boosted audio.

Then, if the board is battery power cycled, it comes back with both
“font directory not found”
“SD Card not found.”

If USB is then connected at this stage…the board plays boot.wav and all works fine!?

Never seen this before. It’s like D61 symptoms but not.

ok so another thing here I didn’t notice before is that when you unhook USB, the sound goes back to fuzzy, which is odd because the battery runs the booster. It should be clear as when you added battery power before.
So that means you’re not getting battery power everywhere it belongs, including the audio booster and the SD card.
Maybe an RCP issue? Don’t see how though since battery power DID kick in while on USB and kill key was pulled.

This is a bit of a weird one.
My best guess is that this is a ground plane issue, which would mean that the BATT- connection is bad somehow, or possible that the BATT-/GND bridge has been cut.

Another possibility would be that Q7 is not working properly. It’s responsible for both reverse polarity protection for the audio circuit and SD card. However it’s really two separate components in one package, so having both of them break would be kind of weird.

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