Hi!
My first post here 
A customer brought me a EPROM (only one) with V3.1 operating software for the JX-8P.
He asked me to please upgrade the JX-8P with this EPROM.
The problem is that in the JX-8P s/n 694063 there are two EPROM chips with OS version 2.3.
One is IC6 labeled “JX-8P A 2.3” and IC22 labeled “JX-8P B 2.3”.
If i remove the IC6 chip and replace it with the new version chip 3.1 the synth hangs at step “12”
in the power on (self test?) countdown in the display.
Is anybody knowledge how to properly update the JX-8P from version 2.3 to 3.1?
I have seached the Internet to no avail.