I hadn't realised about DE's board layout and I.d. methods, sorry.
It seems that their policy is/was to denote the board in sections from the upper left corner. Numbers are used from left to right, and letters from top to bottom. There are numbers and letters screened onto the board, but only one of each; the '12' is right there, but 'A' is much further away, next to the Cmos test point, C 157 and inductor L 2, below CN 17. So I see 12A as the upper of the two chips, Row 'A' as it were. It's more of a video game practice, I think.
Each chip has pins 7 and 14 for its own power and ground, though the schematic doesn't clearly show this. From your readings, I'd say 14, lower right, is power and 7, top left, is ground. The dot in the chip housing indicates pin 1.
The separate gates of the 7402 chip are;
- input pins 2 & 3 switching output on pin 1 (SP 3 for chip 12A)
- input pins 5 & 6 switching output on pin 4 (SP2)
- input pins 8 & 9 switching output on pin 10 (SP 4)
- input pins 11 & 12 switching output on pin 13 (SP 1)
In this case, the pin used for EN/Blnk pin is the higher number, so 12A's pins 3, 6, 9 & 12 should act together, High in attract mode, dropping Low with a game started and the flipper relay On.
The change shown in your pictures is the gate 8 & 9/output 10 of chip 12B, which isn't used as a solenoid drive; it's further up the chain, controlling the EN/Blnk line itself. That's behaving as it should, pin 8 drops Low to give two Low inputs, so pin 10 changes to a High. 12B does control two drives, SP 5 & 6, but from the gates on its upper edge, i.e. 2 & 3/(1) and 5 & 6/(4). The fourth gate of 12B switches the flipper relay, from pin 13, is that responding? It's an X in both conditions.
I'm worried that 12A doesn't show any change on its upper edge, the gates for SP's
1 3 and 2. Not only that, but all those pins are Low. With Low inputs, the outputs (pins 1 and 4) should be High. Maybe that short circuit has blown 12A, and possibly B.