EPS display suddenly malfunctioning

I was re-installing the keybed in my EPS and when I switched it on, several of the buttons weren’t responding. I switched the machine off, unplugged and re-plugged both cables from the front panel board, and now it doesn’t display anything on the VFD until you press a button, at which point it will display one character in the first space, which changes with different button presses.

The instrument LEDs light up correctly, it reads the OS from the boot disk in the normal amount of time, but nothing on the display but the one meaningless character.

It was working perfectly the previous time I switched it on, which was thirty seconds prior. Between switching it on and everything functioning and the first malfunctioning of the buttons, I didn’t touch the front panel board or any of the internals except to plug in the KPC (on the keybed end, not the mainboard end, so I didn’t touch the mainboard at all).

Any clues?

The symptom you describe means the display is in ‘self-test’ mode - pressing different panel buttons show different characters on the display. This means that the display board is not communicating with the main board, so there may be a problem with the ribbon cable connecting them. Make sure it is plugged correctly.

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Unplugged and re-plugged the cable from the display board to the main board, but no change in behavior.


  • EPS sends MIDI data: note on/off, velocity, aftertouch, both wheels

  • cable between display board and mainboard has been tested for continuity

No change to the display behavior, but this at least indicates that neither the KPC board nor the mainboard are fried.

From the sound of it, you can load the OS and play as a MIDI controller, right? Since you can’t see the display, it would be “tricky” to load a sound, but have you tried that also? Try a disk and hit load > instrument > Enter > bank 1. Worth a try at least.
Also, if some of the buttons still do not work and the display is acting crazy, it sounds like the display/keypad board has an issue. It just coincidently went bad while working on the other stuff most likely. Next step for that is to check capacitors, etc.

Only one left in stock also.

Display board, Ensoniq EPS - Syntaur