Fuses (especially the high voltage one as the filament in them is very skinny) can look good but still be bad.
Put your meter into continuity mode should look like a o))) if it's a standard type meter. Pull the fuse from its holder (you cannot reliably test a fuse in circuit). Test it by holding one of each of your probes to either side of the fuse on the metal caps. You should hear a continuity beep if it's good and nothing if it's bad. (Test your continuity beeper by just holding your meter leads together. The meter leads need to be in the common socket and the one with the omega symbol for ohms. Meters that can test current usually have different inputs for that purpose only. If you get the beep when you touch together you have them in the correct inputs)
If the fuse is bad, replace it. DO NOT, DO NOT, under any circumstances with the high voltage circuit, change the fuse to a higher amperage! There are 3 fuses for the high voltage power supply located on your power supply board (the upper right board in the backbox). F1 is 3/8 amp slow blow for the input, and F2 and F3, they are each 1/8 amp slow blow fuses.
F1 is the high voltage input, and if it is blown, that means something is amiss in the high voltage generation circuit and it might need to be rebuilt. If this is the case, rebuild the entire circuit, do not mix and match components - they are all stressed from age and the fact that this is a high voltage circuit (it generates +100 volts and -100 volts for the display).
F2 is the +100 volt fuse, and if it's blown, it might be something on the display panel itself. Ditto with the F3 fuse, which is the -100 volt fuse. It is possible that the high voltage circuit is generating perfectly fine voltage, but if someone overfuses the output fuses, the high voltage section could blow even if it was fine. This is one of the dangers of overfusing, so don't do it.
If all three of the fuses are good, disconnect the display's large connectors so it's not connected at all (including the ribbon cable). Put the fuses back in making sure you don't swap the 3/8 amp for one of the 1/8 amp ones. Turn the machine back on and with your meter in DC voltage test (usually it will be marked DCV, sometimes with a non-autoranging meter you have to select the 'range' - 200v would be the range to use).
Put the red lead to the fuse F2. Black lead to a convenient ground (there should be a ground braid from your cabinet at the bottom of the head with a wingnut on it that is ground). You should read around +100 volts.
Put the red lead on fuse F3. You should read around -100 volts.
If you have good voltage, turn machine off and plug the display connectors back in. Turn game on. If display is still blank, get up close to the display tubes and see if you see a 'glow' near the bottom of each display. That tells you that the display is getting voltage and the display tube is good (well, good enough to light something).
If at this point you can play the game without the display, there's a couple paths to take. There are 2 resistors in the high voltage generation circuit that like to go bad. R1 for the +100 and R4 for the -100. These are 'flame proof' resistors and must be replaced with the same type. Or, it might be that both display panels are out. This is where having another machine is helpful as you can swap the display into a similar era machine and test it.
You really won't know which direction to proceed until you test the fuses though, and make sure your power supply is ok. Same thing would apply to swapping display panels in that you can swap a power supply board as well.
Be careful when you are testing the voltage that you do not slip with your meter leads. You can also test the voltages when the display isn't hooked up by putting the meter leading into the connectors. The J7 connector on the display board (according to the schematics) carries the voltage. pin 1 is the -100. Pin 2 has no connection. pin 3 is the +100. Pin 4 has a keying plug in it. Pin 5 is ground. Pin 6 is +5 volts.
Cuyahoga Falls, OH
