You can find the latest firmware available here.

IMPORTANT: 4.x requires the PWM kit installed, so DO NOT install 4.x on a 3.x firmware. You can always go back to 3.x afterwards, but the tones will be converted to 4.x format and so will appear corrupted when you go back to 3.x.

Eprom replacement guide JX10
Eprom replacement guide MKS70
Contributed manual
Midi CC description
PWM kit install manual
Sysex and midi CC for release 4.0x
Super JX flash module manual
JX10 bootloader 1.02
MKS70 bootloader 1.02
JX10 firmware 3.22
MKS70 firmware 3.22
JX10 firmware 3.23
MKS70 firmware 3.23
JX10 firmware 3.24
MKS70 firmware 3.24
JX10 firmware 4.16
MKS70 firmware 4.16
JX10 firmware 4.17
MKS70 firmware 4.17
JX10 firmware 4.18
MKS70 firmware 4.18