Wizard of Wor repair log

 

This game uses 6 PCBs – an unusual design.

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!

The shorted capacitor exploded so hard that it actually broke in half.

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.

After finally getting the chip on the board, I was able to test the RAM.

I ended up having two bad RAM chips on the board with the capacitor that exploded.

I replaced the original 4027 chips with 2104 RAM, which is a drop-in replacement.

 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.

9 thoughts on “Wizard of Wor repair log”

  1. This is a really great ‘blog. I’m a HUGE fan of Wizard of Wor and finding technical info, deep technical info, about it just made my day. Tell me, how much RAM did it have? Did the system have a discrete CPU or was it just logic? I’m guessing it was a z80? Or was it a 6809? Is the votrax (if that’s the correct hardware) board in the main cage pictured or is it a separate subsystem?

    Anyway thanks for this cool ‘blog post regardless!

    1. The Votrax chip is indeed on one of the boards in the cage. All of the game circuitry is in there. It’s a pretty unique design, and the only other game that runs on similar hardware is GORF.
      It has 16 RAM chips on each RAM card, and each “4096 word x 1 bit” RAM chip equals, I think on an 8-bit CPU, 512 bytes, so I think the game runs on 16k of RAM. I’m not an expert by any means so my calculations could be off.
      You are correct, the CPU is a Z80. Glad you enjoyed reading my post!

  2. Great work !! Thank you so much ! Also thank you for the component links !
    Where can I find this test rom exactly ?

    Best regards
    Marco

      1. Excellent info, I’m attempting repairs on my WoW which just went down. Once I have the test rom programmed, where do I install it, at which location and on which board?

        Regards,
        Ivan

        1. The file included in the zip should have this info, but just in case, the ROM should go in position X1 on the ROM board.

  3. hey there
    are all the titanium caps the same on all the boards? I’m fairly sure its my CPU board thats giving me issues as I get no 12v if its plugged in but I do when I take it out of the slot.
    LMK ~sm

    1. Hi,
      Yep, that sounds like it could be caused by a shorted tantalum cap. That link to the replacements I provided should work for all of them. I would just replace them all so you don’t have to worry about another one shorting out down the line.

  4. Standard electrolytic caps – 22uf @ 50v axial – will work just fine and are a lot cheaper than using tantalums, plus they won’t explode.

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