Working on a Williams Laser Ball with wonky displays on player 3 & 4 only.

It has a new set of LED displays.

In display test player 3 & 4 display the following digits :

Correct / Player 3&4
000000 / 888888
111111 / 999999
222222 / Blank
333333 / Blank
444444 / Blank
555555 / Blank
666666 / Blank
777777 / Blank
888888 / 888888
999999 / 999999

There's also a single bad segment, the bottom segment on player 4 thousands digit never turns on.

Video :

I could use some ideas what to check into for this problem?

I have a logic probe to help figure it out.

The video shows that it's using Wolffpactech displays.

Found the schematic here, https://ea220797-3ca6-4fed-a391-47553096ec99.filesusr.com/ugd/07f9d3_be3cf58e859849b18712cbb95ea4155b.pdf

Looks like Q1, which is a ULN2803 could be the problem since it's driving display 3 & 4?

EDIT: OR possibly U3 or U4 since those are inputs to Q1.

wolfpactech (resized).JPG

Thanks to your great advice Quench, the displays are now fixed and working perfectly.

Using a logic probe on IC chip U2 on the master display there was good pulse on pin 4. It was also noticed that all 4 displays worked correctly for a brief time after powering off / on and starting the display test, than started to fail again soon after.

Next I noticed pushing down on the pins of U2 with the logic probe allowed the digits on player 3 & 4 to be temporarily started all working during display test. So the solution was simply reflowing the solder on all the pins of U2. This IC had been poorly soldered to the board and reflowing the solder was the solution.

Next, the individual display with a segment out on player 4 1000s digit, that was solved by reflowing the solder on that individual 1000s digit LED. Once that was done the segment of the display was working correctly.