I have an older 4020 with an 88 control and the main board is a 1400-2. When I hit Jog it flashes on screen then goes away. I have tried everything and finally put a 1400-1 board in and it works fine except this isn't my board and it's very old now. I sent 1400-2 in for repair and they replaced CPU but still same issue. I would keep the 1400-1 but DNC doesn't work and it skips numbers and feed rates or makes a F30 into F3 and -10 into 10. Errors I get with 1400-2 are C (spindle) but spindle works fine. This issue started when I dropped a leg of my 3 phase power on startup one time and then hooked it back up and this was the issue not sure if coincidental. I've pounded on jog, zereo pointed memory everything I could find.
There was an issue when using newer 1400 cards with old version Keyboard card.attached to the keyboard PCB-0012 REV F (this though doesnt seem like the problem if it just showed up out of the blue) or maybe it is the keyboard interface.
Have you run you diagnostics DI enter G 0 3000 enter
I finally figured this mess out. Turns out that the ribbon cables to the card attached to keyboard have lots of stuff going on and just needed cleaning.