Right on the heels of my project Space Shuttle that I got 100% working, I just picked up a project Gorgar

Gorgar boots and can start a game, "Gorgar speaks!", then goes right into tilt. I haven't had time to do much troubleshooting, but I did unplug the switch connectors and go into switch test mode, and it reads a series of switches on the second row, one of which is the ball roll tilt.

So we've got a problem on the driver board. I haven't dug into the schematics yet, but does anyone know off-hand what would cause switches, perhaps even a whole row, to be registering even when the switch connectors are unplugged?

Thanks!

How's this for an interesting issue? I removed the Switch Matrix PIA and entered the switch test. It registers switches 1, 2 and 8. Should the switch test be registering anything with the PIA removed?

I've isolated the issue to the driver board. My Alien Poker uses the same driver board and when I swapped AP's board into Gorgar, Gorgar no longer registered the phantom switches.

I don't have replacement female headers for the 40-pin interconnect, but I did replace the male pins just to see if that would have done anything. I will replace them, but the tension on the female pins seems good, so I'm inclined to blame the phantom switches on something else.

The 3 PIAs are socketed and swapping them around doesn't change the behavior at all. One of the sockets showed signs of corrosion. I replaced it with SIP sockets and nothing changed.

I'm not sure what else to blame other than possibly the HEX inverters.

Is more than one PIA responsible for switch detection? I was thinking based on one of the board diagrams that it was just one PIA, but looking at the traces, it appears to connect to some of the pins on the middle PIA (that's the one where I replaced the socket). I don't understand how the game could be registering any switches if that PIA is removed altogether... Just to see what would happen, I removed the middle and right PIAs and STILL get phantom switches in switch test mode...

Anyone have any ideas?

I did a bit more troubleshooting before calling it quits tonight. It occurred to me that even with swapping PIAs around, the constant in all of it was the socket for the switch PIA. It looked like a newer one, so it had likely been replaced at some point. I checked continuity of all pins to a corresponding point on the board and found one that wasn't making contact I assume due to a cold solder joint. I failed at adding solder to fix it and opted instead to replace the whole socket with SIP sockets.

That seems to have cleared up the phantom switches! I can now play a game without it going into tilt mode.

I checked that all switches register on-board by unplugging the switch row and column connectors and using a jumper between the rows and columns. Any remaining switch issues are going to be on the playfield or connectors.

It hopefully won't be too much more work getting this game playing 100%.

I love it when I'm able to bring a non-working game back to life!