I’d worked on a few prior – but they were for friends and I wasn’t sure I wanted to start taking them for repairs. The boards prior to this one I had made up a bench adapter. They had minor issues and were mostly working.

The adapter for my bench trackball was done, except I didn’t allow for testing the second trackball! In cases like this – I add another connector to swap P1 and P2 trackball inputs between my controller and the game board. The bench harnesses pay off in time spent making them on the second repair.. The first time through it’s an investment into the shop. The typically take 2-3 hours to assemble and test.

Board #3 – In for repair

The board arrived with two partially broken bus bars. Further diagnosis revealed an address decoding fault on the sound CPU. The cartridge board I had suspected damage by power surge – turned out at least 12 of the mask ROM chips had failed. CPU Board would actually boot into diag mode.. and then every individual diag screen didn’t work correctly after that. When I first saw this wiring, I thought it was some sort of repair hack. Turns out this is factory on the early versions of the board (I believe).

Board has bus bars like the Bally MCR games. The last 6-8 contacts were snapped on 2 of them.. I cut the broken parts off and re-jumped with Kynar wire.

“NO CARTRIDGE” was the first error. I probed around with the scope and saw signs of life on the cart. Pulling the mask roms, they were all coming up FFFF. I wasn’t sure if I was reading them wrong or if they all took a power hit? I’ve only worked on a few of these so some of the time was just understanding the board set.

The built in sound test said that the sound CPU was not responding. It is a 6502 – so that was a good place to start. I made a FPGA Tester configuration to just see if I could read across the interconnect for RAM and ROM to isolate and diagnose the sound circuit. After a fair amount of probing and testing, etc. The ROMs were not reading – I burned 2 replacements and they still were not reading, but I knew mine were good. The mask ROMs had issues (see below). The RAM looked like it was partially working. Finally I removed the RAM at location 16M, installed a socket, put in a new RAM and the sound test started working and it cleared the ROM read errors. Confirmed the Pokey was functioning correctly and that the mask ROM were actually bad. This confirmed I was reading them correctly on the bench.

One more test, I put the original RAM back and it also worked? Not sure why, maybe there was a hidden short under it? But at least I had a portion of the CPU board talking to the cart. It was a start.

Now that I had something working. I decided to pull and test all of the mask ROM on the cart. Each one read bad until I finally happened across one that worked. The good news is I was reading them correctly, the bad news was the board needed 13 replacement EPROMS.

Once I got all of them installed – very similar results in diag mode. In game mode, wiggling 2-3 of the ROM in the sockets got me an actual game with some partial graphics! Replaced 3 faulty ROM sockets as an initial step. Now that the game booted – some of the diag worked correctly and some screens didn’t.

At this point – I popped a few more covers off and many of the sockets looked like this. Replaced all ROM sockets on the cartridge board that had chips in them.

While doing that, found this:

Factory – never soldered cap. Didn’t effect anything – but I soldered it back in place.

Once I got all of the ROM and sockets replaced and stable.

I got this. Fully functional – with missing graphics blocks. This took a while to hunt down as well – but most of the board was working – so I was happy with the progress.

Replaced a PROM @7A, which had a single corrupted data bit and was responsible for selecting the correct graphics and picture data, restoring full playfield graphics. If you look at byte 0 – the good PROM has ‘e0’ and the bad one has ‘f0’ – that’s it.. a single bit flip causes those missing blocks. I ran this one over 50 hours in total. The owner and I (who got this off eBay) determined that it was originally a barn find. Which tracks. This set had not seen power in many years.

Board Works!