Well, still no luck in solving this. I replaced the capacitor on one of the display boards with a brand new one from Great Plains Electronics and there was no change, even when I unplugged all of the other displays. Then I tried changing the lug that the input voltage is attached to on the smaller transformer in the cabinet. It was on 115. Tried 100 and the displays got a little brighter but still have the same constant slight flicker. Moved it to 130 and the displays became dimmer with the same flicker. I put it back to the 115 and back to baseline brightness with the same flicker.
Any other suggestions as to what might be causing this? Thanks.

Thank you. I will see if that is possible.
This is my only Gottlieb game so I have nothing to compare the symptom to and have little experience with the system.

I don't have another Gottlieb game. I had the same problem with the original power supply board as with this new board from Rottendog.
I tried disconnecting the driver board and the sound boards but there was no change. I have ordered a new line filter for between the power cord and the transformer. Just a shot in the dark but for $14 I thought I would give it a try.

I replaced the line filter in the bottom of the cabinet next to the transformers with no change in the display flicker. Guess I need to decide if I want to spend the $300 on a new set of displays.

The new displays are low voltage LED and run off a plug into the service plug in the front of the game. I will scout around my area but pretty sparse around here.

One other thing I have noticed is that the slam switch does not work at all. I manually opened and close the switch which is normally closed, nothing happens even after I cleaned the switch. Even after disconnecting the wires and directly connecting the 2 wires that go to the switch, nothing indicates that the cpu notices anything. This happens with either the origanal cpu or the Rottendog replacement. I have noticed that the flickering effect is worse on the 2 Rottendog boards that I tried than the original. I have tried contacting the establishment I bought the game from but they have not provided any answers as to why the slam switch does not work.. Any suggestions?

Does this mean the slam switch is inoperative or just ignores lack of contact on boot up?

I saw that mod for the original mpu but I don't want to mess with my new Rottendog board and void any kind of warranty or anything. I also checked to see if it had been done on my original board and it had not been done.

Ok. More information.
On the original board, someone at some point unknown had soldered a jumper across the cap and resistor on the mpu next to the z26 chip disabling the slam switch and all the problems it can cause so I don't think the slam switch is the problem. I did not know about this fix until I found it on PinWiki but it is why the slam switch does not work with the original board.

In comparing the display problem with both the original board and the Rottendog board, I have noticed a difference in the appearance of the displays when the original cpu is in the game and when the Rottendog board is in the game. When the original board is in, the displays show a slower pulsing brightness. Brighter-dimmer-brighter-dimmer. Looking carefully, the filaments in all of the displays seemed to be fluxing brighter and dimmer. The outermost digits in each of the displays seem to have this problem more prominently than the inner digits.

When I have the Rottendog board in the pulsing is quicker and more pronounced on the verge of a constant regular flicker. Again, the outer digits are more pronounced.

I will try to contact the guys at Rottendog tomorrow to see if they have any thoughts on why there is a difference. The problem with the displays is less apparent with the original than with the new board.

Any suggestions are appreciated.