It could be a bad ribbon cable but since you have both Alpha Numeric displays acting out, I am going to bet that it is one of the chips on the display driver board. Problem is that these chips are just about obsolete and very expensive if you can find them. If that is the case there are three options. Figure out which chip is bad and replace if you can find it. See http://hansbalk.home.xs4all.nl/rep/sys11/index3.htm#display the section on More Segment Problems: the UDN7180 chip. Will show you how to chech the chips with a logic probe. Not very difficult but as I said, finding the chips will be a bear.
$85 replacement drive board. Your displays look nice and bright so this should fix you up. I have never personally used this board so I do not know what kind of support you would get.
This is a bit more expensive at $199 but this would replace both the board and the displays with LED displays. Less stress on the power supply because it eliminates the need for the High Volage 100 volt for the displays. You can completely remove that fuse all together. This will also create less heat. I personally know Brett Davis the creator and designer of these boards. His customer service and support is second to none. I but a set in an old Firepower and it made a big difference.
As to which route you want to go, depends on the overall condition of the machine. I have owned a High Speed in the past and this in one of my favorite machines.
You can interact with the ChatGPT Bot in any Chat Room and there is a dedicated room. The command is /ai followed by a space and then your ? or inquiry.
ie: /ai What is a EM Pinball Machine?