Well, I received and installed the new replacement board on the 13th,
so I've had 10 days to properly test it.
First, the board looks exactly like the old one, same numbers printed
on the board, etc. Turning the shafts feels exactly the same as the
old one so I think they're the exact same part. Not nearly as robust
as the A3000.
Before I completely removed the old board I wanted to see if it
worked perfectly while unmounted like it did a month ago when I was
experimenting. So I unscrewed the old board from the chassis leaving
only the wires connected. And it didn't jump at all for the 5
minutes I spent twirling the knobs. I don't know why the old board
jumps like crazy when its mounted to the chassis but seems to work
fine when dangling with only its wires connected. Oh well.
The new board installed easily, and has worked flawlessly for 10
days.
The installation is very easy. Just unplug your harddisk and remove
it with it's 2 mounting bars. Carefully remove the LCD wire from the
LCD - it pulls straight out. Then you'll need a pair of needle nose
pliers or very small screwdriver to remove 2 connectors that connect
the encoder board to the motherboard - one connector is on the
motherboard, the other is on the encoder board. (You may want to
mark the direction the connectors are inserted with a felt tip pen).
Unmount the old encoder, install the new one and reverse your steps.
Pay attention that no wires get pinched anywhere, especially under
the harddisk.
I'm not sure how much longer Yamaha plans on manufacturing these
boards, but at $70, it may be worth buying a spare to keep around. I
do know they don't make parts for the A3000 anymore. I expect this
new board to work great for a while - the previous owner smoked so I
believe that was the cause of the first problem.
It nice to have a properly working hardware sampler.

I hope this
helps somebody.