Just bought a High Speed and everything about the game is working fine except for the Player 3, Player 4, and credit/match displays. They are black as night. Player 1 and 2 are working fine. All segments working properly and display is bright.
Here is what I have checked:
All ribbon cables seated correctly.
High Voltage coming into the display board - The +100 registered 107 volts. Is that ok? The -5 and -100 were right on.
Using Clay's guide I learned to check the voltages on the UDN6118 and UDN7180 chips and they all tested ok.
Not sure where to go from here? What should I zero in on that would only impact the player 3/4 and credit/match displays?

Unfortunately, I don't have any other machines of this vintage so I have no spares to test in the machine.

Any help would be greatly appreciated. Thank you!

I don’t have a logic probe.

Didn’t realize they were only $20. I will have to buy one. Thank you!

If that component was bad would that knockout the 3&4 player and match/credit displays?

Thank you for the advice. I will check out the tutorials.