Dig Dug Resurrection

larrylemming

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This is a repair log for my second ever board resurrection, Dig Dug. (Galaxian was my first -- bad CPU, bad RAM, questionable ROMs, and a few bad discrete chips in the video section.)

This board was an eBay find -- listed non-working with a static screen of garbage. I figured I'd take a chance. It would also give me the opportunity to develop a good test bench.

I got the board and confirmed the seller's description -- static screen of garbage. I did the following:

1. Tested all 3 Z80's in my Galaxian cabinet. Two were good; the third fell apart as I was testing it. This got the board to attempt to boot itself.
2. Replaced all RAM chips on the board. Got a little further!
3. Cleaned and re-seated most of the IC chips. It boots!

But, it still had graphical issues. First, garbage in the sprites -- this was fixed by further IC cleaning. Secondly, every line of the playfield was duplicated. After verifying that most everything on the "Playfield Generator" page of the Dig Dug schematic, I turned my attention to the custom chips. I knew a little bit about what some of them did, but a little research didn't turn up much, certainly not enough information to satisfy my curiosity. Eventually, I removed the 00xx and tried booting -- the sprites were all fine, but the background disappeared. I then plugged it into a spare socket, which I then in turn plugged into the motherboard. This allowed me to lift each pin of the IC in turn until I verified that one of the inputs was indeed not responding to anything.

I did some shopping for replacement Namco chips, but most everywhere I looked was out-of-stock. FPGA Arcade had replacements, but for his asking price, I wanted to verify that the 00xx was the culprit before I wasted my money.

Then, one day, out of the blue, I found a non-working Galaga on eBay for a price I could afford. (The seller claimed that everything worked except for the input. Given how many chips were missing from the board, including some chips cut off at the legs without even being de-soldered, I'm not convinced. But that's a project for another day.) I removed the 00xx from the Galaga board, installed it in the Dig Dug board, and -- the board's not booting again. Re-seated some IC's (I really need new sockets), and... Presto! Fully working Dig-Dug!

The monitor in the picture is indeed a VGA monitor. I'm running the video through an imported CGA-to-VGA converter I picked up on eBay (Happ sells them too.) They work wonderfully, and I highly recommend them for a test bench or even as a cheap way to replace a monitor. After all, VGA monitors can be found in surplus fairly easily.

Total investment: 5-6 hours, plus ~$130, including the Galaga board which is, at least, still good for parts.

Next up -- building a cabinet to house this board... eventually. I have a few Nintendo Unisystem boards that need cabinets first.
 

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Congrats!

The best thing you can do for that board is to use good quality dual wipe sockets on those pesky custom chips.
 
Nice work. Those original IC sockets are a common problem. All the intermittent issues I was having with my Dig Dug went away after I replaced the IC sockets.

FYI, the 00xx custom chip is the same as the Pac-Man "284" VRAM addresser, which is often cheaper and easier to find.
 
FYI, the 00xx custom chip is the same as the Pac-Man "284" VRAM addresser, which is often cheaper and easier to find.

Good to know, as I'm still down a 00xx after I stole the one from the Galaga :p

I've heard conflicting opinions on what kind of sockets to use. I've heard some people swear by machine-pin sockets; other people prefer dual-wipe sockets. I personally prefer the machine-pin type as they're easier to install and seem to be a bit more durable. They're also significantly more expensive.
 
And I prefer the dual wipe sockets because the machine pin ones tend to damage the board. Machine pin sockets have a "shoulder" to their pins, which tends to get soldered to the top of the board during soldering. This in turn makes them VERY hard to remove without damaging the board further. I've seen boards severely damaged because someone installed machine pin sockets improperly. Good quality dual wipe sockets make a very good connection with the chips, and will function just fine. Plus, they're cheaper.

-Ian
 
I despise machine-pin sockets! It usually takes me minutes to insert a 40-pin chip. If I try to go faster, I bend or damage legs. I have tried varying techniques but so far no joy.
 
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