Space Invaders Board Repair Troubleshooting

Officepot

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Hello all, I have the troubleshooting guide for MIDWAY 8080 board sets and am attempting to follow it to determine my issue. I have no known good PROMS so I am utilizing a Braze kit. The Space Invaders arcade was working well till I left it on for about an hour the other day. Then it started beeping over and over at me and resetting.

I then went through the Braze kit manual and determined it was beeping 8 times. The beeping was not the expected "shoot" sound either it sounded odd, see video here. I replaced the corresponding RAM, G15. After replacing the RAM it does not beep at all but replacing the ROM DID remove the lines and dots on the screen as seen in the video, it now resets over and over without any lines present on the screen. Reinstalling the original RAM makes the bad lines return to the screen, but it does not beep at all anymore.

I can see data coming out of the RAM on pin 7 of G15. I want to test the RAM further, but in the 8080 troubleshooting guide, it says to find bad RAMS by using the garbage on the screen and ground out the outputs... but I have no garbage. How can I test for bad RAM in this scenario?

I did another test, I removed the BRAZE kit and reinstalled only the 8080. With the 8080 installed and no PROMs I get what the manual refers to as "GOOD VERTICAL LINES", which SHOULD be an indication of good RAM. I went through the "NO RAM TEST" section of the manual, since I assume the braze kit not starting is similar to the RAM TEST failing to start, but did not find anything out of the ordinary, which circles me back around to checking the RAM.

So my friends, what should I do next? Any help is appreciated!!
 
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