Beaky,

Went out and check the voltages, they are as follows (pins go from right to left on the machine)

Player 3

Pins 1 - 16
-0.8   3.7   4.2   3.8   9.1   82   -93   3.2   2.9   3.2   0   6.4   2.3   3.8   0   5.4

Pins 24 - 39
3.2   0   6.4   3.8   6.4   0   5.4   -95   3.2   1.1   83   0   6.5   0   6.5   -1.3

Player 4
Pins 1-16
-1.4   6.7   0.5   6.8   16.7   17.4   -10.8   5.4   0   5.4   3.5   6.5   0   6.4   1.9   5.5

Pins 24-39
5.5   1.9   6.4   2.5   6.5   1.6   -3.7   -12.5   -3.6   -0.8   18.3   -1.5   3.7   -1.9   3.7   -2.1

The other thing i noticed is that some seemed to fluctuate a bit, dunno if this was when the display was meant to be lit up during attract mode?

sounds like one or both of the displays are stuffed.
on player 3; the 82v &  83v on pin 6 and 34,  plus the -93v & -95v on pin 7 and 31  are to high : and on player 4; the 17.4v & 18.3v  and the  -10.8v -12.5 on the same pins are to low.
on pin 34 i have 54v, i will check pins 6, 34, 7 and 31 tonight, to memory the -95 was around -63v on mine.
i will have a look at the scematics tonight also and see if i can think of anything else but you may have to take both of the displays out and fit 2 new ones or take out  player 4 display  and check the voltages without the display fitted.

might be easier to replace both displays. at least one is crook and like strange ways problem one might be shorting out internaly.

one more question does any of the 2 displays have a slight orange glow near the pins at the bottom on the last few digits?