I have been working on a Wizard of Wor machine that wouldn’t start. The only thing I got was a vaguely green screen and a buzzing speaker. I began by removing the socketed chips one at a time and cleaning them with a high quality plastic eraser and a Dremel wire brush when the tarnish was too heavy. After this I sprayed Deoxit into all of the sockets and reseated the chips several times each.
I checked the power supply and found that there was no voltage on the +12v line. If all voltages are not present, the supply will not send the 5v “power good” signal and the game will not boot. My first thought was to replace all the capacitors on the power supply since they are at least 37 years old at this point. However, I still didn’t get any change. I also tried changing out the variable regulator that controls the 12v to no avail.
It was suggested to me that the small tantalum capacitors on each of the 6 game PCBs are known to short out. While I was testing another point on the power supply, one of these capacitors on one of the game’s two RAM boards exploded, so I went ahead and replaced them all with these. After that the game booted!
However, the display was completely scrambled. Another tip I got was to adjust the horizontal frequency control deep in the recesses of the monitor chassis. Turning it all the way up, I was finally able to get a steady picture, but it was a bit unevenly projected, most likely due to old capacitors. There were also two sets of vertical yellow lines at even intervals across the screen. The cause of this turned out to be some bad RAM chips.
To test the RAM chips, I burned Mark Spaeth’s excellent GORF test ROM since Wizard of Wor uses the same hardware. I had to create an adapter to burn it onto a 2532 EPROM because my programmer isn’t compatible with them out of the box.
I also had to bend a pin out and wire a jumper in place so it would not be damaged by the ROM board (which still uses the original mask ROMs.) I found this information in the readme file for an earlier Wizard of Wor test program, WOWMD.
Now the game is up and running. I need to replace the capacitors on the monitor to correct some display geometry issues, and that’s it. I’m also planning to put heatsinks on the game’s special Astrocade chips since those are known to sizzle, and without them we’d have a dead game on our hands. Since the original heatsinks that Midway used are pretty hard to come by now, I found some alternatives I think will work nicely for about 50 cents each.