I had a display problem on Rollergames. I touched the ribbon cable and it made it better/worse. At the time I bought a new ribbon cable and a new ribbon connector, which I squeezed on the existing ribbon cable. Everything was fine for months.

Then I installed a remote battery holder, and after putting the CPU back in the game the display had errors again.
When I pulled the new installed connector the top broke off, so I put in the new ribbon cable I had bought and was never installed.

That didn't work either, every segment was fully lit for the digits that were controlled. So I put in the old ribbon cable, and saw I forgot to connect a connector which is used for the display as well. After that everything worked fine again. Remember: if something does not work after some work has been done: check that again.

But the new ribbon cable still caused the problems for all the segments. What was the problem with the new ribbon cable? I had bought one with an additional connector (used for games with the display configuration next to each other like Elvira), and the extra connector was making shortcircuit between all of the wires.