[William Sommerwerck]

Sure enough, removing the nut from the phone jack
allowed the whole unit to slip rather easily out of
the case

Sheesh. You "shoulda" known enough to do that,
at least. Good grief.

Its not really self evident that the jack is connected to
the PC board. When I took mine apart, I certainly did
NOT think it was that way. I eventually figured it out,
but it took a while. I assumed it was just a raw jack
connected with loose wires to the amplifier.

This sort of assembly is not that uncommon, as it reduces manufacturing
costs. It also makes testing the amplifier a bit easier. I've seen expensive
equipment that did the same thing, making the device virtually
unassembleable.