What would cause the 7-segment display on the MPU to not light up at all? I was going through the 5V checks listed below and everything was good. Turned it off and went away for a little bit for lunch and now when I power it up the display is blank instead of garbled. I had replaced C30 and it started working and then after playing it for a few hours turned it off for the day. Next time I turned it back on the display was garbled again (leading me to think maybe C30 was fine). Now I have no display, but still have the 5v at the points below:
Test for Proper voltage on the boards.
Your game will never run if you don't have +5 volts on the CPU board. But first you must test for ground on the CPU board. To test for ground, turn the game off and set your DMM to "ohms". Make sure you get zero ohms from the ground test point TP1 (to the left of the batteries) on the CPU board, to the metal shield or ground strap in the backbox.
Next set your DMM to DC volts. Turn the game on, and test for +5 volts at TP2 on the CPU board (TP2 is to the right of chip U21). Make sure the black lead of your DMM on ground (backbox grounding strap). Now test for +5 volts right at the chips themselves. For example, test for +5 volts at U15 (the 6808 CPU) at pin 8. The 2764 EPROM at U26 and the 27256 EPROM at U27 will have +5 volts at pin 28. The 6821 PIA's at U10, U38, U41, U42, U51, U54 will have +5 volts at pin 20. Remember, pin 1 of all chips is by the "notch" in the chip. Also there is usually a white "dot" printed on the circuit board to show pin 1.
Actually, I just did a test and I have 12 ohms between the GND test point and the metal back panel. That doesn't seem right at all. I touched the top center bolt, the one the ties the board to the stud to the metal back panel, and I got 9.8 ohms!?! What on earth is going on here?
EDIT: Did the test with the game off and I get 0.7 ohms. So now I'm just back to why the 7-segment is out. But also, why would that GND TP and back panel read 12 ohms with the game on?