Vertical bars run through the dot matrix display. Swapping the display, the DMD controller board and all the ribbon cables with known-good parts changes nothing.

Moving vertical bars across the DMD with known-good display parts: CPU board fault

Cause: A fault on the CPU board (a replacement aftermarket board in this game).

Checks

• Unplug the ribbon cables to the sound and Fliptronics boards so only the DMD controller is connected; if the picture changes, the problem is on the shared data bus.
• Reseat the socketed chips on the CPU board.

Fix

• Swap in a known-good CPU board; repair or replace the faulty one.

Systems

• WPC Fliptronics

Games

• Fish Tales

Related tips

• DMD dead though display and controller work in other games: CPU board fault
• Blank display, garbage or diagonal lines: reseat ribbon cables
• Vertical lines and garbage on the DMD mid-game: press the ASIC back into its socket
• Dot matrix display goes blurry within minutes
• Narrowing a switch matrix fault to the CPU board, wiring or opto boards
• CPU board completely dead
• Switch matrix chips on the CPU board
• Reboots at start-up and when flipping: flaky power connector to the CPU

Source: Pinball Repair help group!! (Facebook group)