Space Invaders PCB Repair

I've had this Space Invaders board a while along with another one but kept putting off looking at it. Mainly because my 8080 fluke pod has never worked right and even when I thought I'd fixed it and had it passing self test it would still fail to do anything outside of self test.

Anyway lets see how far we can get without the fluke.

This is basically the screen you get when the reset circuit isn't working on the power supply but as I am using a jamma adapter I've tied the POR (power on reset) to ground via a resistor and it still didn't make it past this screen even if I pulled the reset pin high.

I already knew the cpu and eproms were good from when I had a working board so I moved onto the logic as even if any rams are bad it should still boot. The HP comparator flagged a 7486 @ A4 saying output pin 8 was bad. I checked it with the logic probe and it was stuck high, shorting it to the input pin next to it and the board booted.

I replaced the 7486 with a 74LS86 which worked fine and it booted every time. The problem now is the screen is a complete mess so we have at least one bad ram. I tried the two different test roms but couldn't work out what either one was reporting as bad.

So I did the old trick of removing all the roms and booting to get lines on the screen then shorting pin 7 of each ram to ground until things look better.

I ended up replacing two rams and using some turn pin sockets off of a scrap bootleg board.

It's alive!

There was just two problems that remained the missile shot sound was very high pitched and the launcher exploding sound when you die was missing completely.

This very helpful page suggested a bad 4006 but it was actually the 4030 chip next to it @ P5.

The motherboard is a L000 revision that I couldn't find anything online about so I had to figure out how to strap it for 2716s myself (Intel type not TMS). It's basically the same how you strap other revisions but S1 (A9) is not connected by default and there's a few more pads on this one.

Repair complete.