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2.4.5. is considered by the system as a major fault, which means that the pinball will halt, when it detects this error. 2.4.5. is caused by a "SHORT IN DRIVER". In general, this comes from a burnt coil, power transistor, or both.
But sometimes, after checking all coils and transistors OK, the error 2.4.5. is still there. In such a case, the problem could come from the short/open test circuitry which resides in the mux board.
This part of the Mux board often fails. That might be the 7400 or the 7445. But it is also worth it checking the 10x2N4291. A dead component here may distort the return values of the switches on AB return lines. Then, an accidental 2.4.5 may result. Always check the 7400 and the 7445, when you get a machine that was previously in an unknown condition. Also check the flat cable on MA and make sure connections are good.
Sometimes, after entering attract mode, the displays are flickering 44444/00000 on all 4 players. The selftest has completed successfully. But the pinball is out of control. Pressing the replay button has no effect. in 90% of cases, this is caused by at least "tilt" and "replay" switches simultaneously seen (by MPU) as closed together. The pinball then thinks it is entering "open coin door" mode and starts to display representation areas. By construction, it starts with area #4. and since replay button appears to never being released, the display alternates showing area number (4) and its content (0). And it cycles forever between these 2 screens, since no switch looks to be released.
This means that the switch matrix control circuitry on the mux board is wrong and that several lines are locked up.
Culprits are generally the same (mainly on returns A&B) as in 2.4.5. forever