ISTR the 4231 is definitely on the 5v side of the bus (hence would be affected by a faulty HDD or cable fiddling with the signals). I think the USB slave *might* be too - don't have the cct diagrams to hand.

As the player works much better with the HDD not plugged in, I suspect:

- HDD
- Cable
- HDD header on PCB

Got another HDD to try it with?

Hugo