Korg Poly800/EX800 Users

Just another post :) I would like to know if the noise using the 
headphones is a "feature" of the Poly-800 or I have to search for 
another problem in the circuit board.

Plus, what type of eprom should I buy to make a rom selector so I can 
use the EX800 rom when I fix the Midi IN port on my Poly? 2764?

Plus^2, the repair manual is impossible to find to me. Anyone has it in 
pdf or similar format? It would be very great.

Thanks a lot!

Manu