I found some really cool JX-3P tricks and old tech repair stuff for isolating voices and other things like that. Hope you guys can use them.

-- JX-3P Test Modes:

If you hold down the 1 button while powering up you are actually entering a
test mode. The first 6 LEDs come on to show which of the 6 voices you are
playing. If 1 voice was bad the service person could quickly determine
which voice needs repair. Also, there was a way to enter test mode with
rotating (hold down 1) or numbered (hold down 2) voice assignment.

-- Hidden Bank Access.

16 extra slots for user tones.

 Hit Tape Memory.
 Hit key 5 and hold it.
 While still holding key 5, hit Tape Memory again.
 To reset to normal operation, hit Tape Memory twice.

-- Hidden Bank Tape Interface.

For saving/loading tones in the hidden bank.

 Before hitting Save, Verify, or Load, go through the
 Hidden Bank access steps described above.

-- Poly II Mode.

This differs from standard Poly I mode in that only the
last note or notes played receive their natural release
length, and is much more suitable where certain types of
staccato playing to slow fade effects are required.

For use with original 32 presets:

 Hit Tape Memory.
 Hit key 3 and hold.
 While holding key 3, hit Tape Memory again.

For use with the hidden bank:

 Hit Tape Memory.
 Hit key 6 and hold.
 While holding key 6, hit Tape Memory again.

-- Sequencer Lights.

The LEDs light up as sequences play - cute.

 Hit and hold Rest button.
 While holding Rest, hit Start/Stop.

-- Manual Sequencer Play.

 While in overdub mode, hit Tape Memory to advance
 sequences manually.

-- Modulating With Noise.

 Hit Group B button and key 10.
 Hit Group D button.

The following two modes were part of an EPROM update - if they
work you've got it...

-- Dynamics When Played From A Touch-Sensitive Module.

 With JX3P off, hit and hold key 5.
 Turn on power.
 Keyboard will cease to function (Local operation off).
 Synth will now act as a touch sensitive keyboard.


 Hit Tape Memory.
 Hit and hold key 7.
 Hit Tape Memory again.
To reset the JX3P, turn it off, then on...

-- For MIDI Channel 3 Operation When In Dynamics Mode.

 Turn on dynamics operation as detailed above - via
 either method.
 Hit Tape Memory.

-- To Turn Your JX3P Into A Tekkno Rave Machine.

 With JX3P off, hit and hold *T*ape Memory.
 Turn on power, then hit *R*est.
 Then press keys 3, 0, and 3 in sequence in a squelchy manner.
 Now kill yourself.