Delving into the Pac-Man Cocktail
We're gearing up for a trip back home to visit the family for Thanksgiving, so not much is going to happen next week on any of the machines. This did make for a good excuse to work from home today. While I was sitting on con calls, I decided to start working on that (Ms.) Pac-Man.
Earlier in the week, I had gotten the bright idea of pulling a Wells Gardner K4600 monitor from a Defender off the shelf and testing with the Pac. The perceptive reader may note that Ms. Pac/Pac-Man is a vertical game and Defender is a horizontal game. Well, the Electrohome monitor that's in the game appears to be of horizontal orientation, so I thought I would be OK (more on that momentarily).
The first challenge I ran into was the fact that the interface board used in the 4601 from the Defender is designed to run off separate X and Y sync signals (positive). Pac-Man uses a negative composite signal. After a bit of thought, I ran down the the garage and pulled the video interface board out of the W-G monitor in my Galaga. Once I had everything wired up, I fired up the game. Voila! I had video. Oh. I had scrambled video. Crap.
At this point, I had two possibilities. The video generation circuitry on the Pac board might be bad, or the interface board I had pulled from the Galaga might be bad because the monitor is dead.
Once again, brilliance struck and I remembered that I have a Ms. Pac upright downstairs. Grabbing the main board out of my cocktail, I took it downstairs and plugged it into the Ms. Pac (which works, by the way). Unfortunately, while I got a clear picture, I got a clear picture of all "F's". On looking more closely at the board that was in the Ms. Pac, I discovered several hacks centered around a voltage regulator and some large diodes. After a bit of research, I happened on the fact that Midway had built voltage regulation into the Pac boards. Since my Ms. Pac had been "upgraded" to a switching power supply (which provides +5 and +12VDC), it was no longer necessary to have a bridge rectifier circuit on the board. Well, when I plugged my board from my cocktail into that harness, there was no AC voltage provided, so it couldn't initialize. Oh well. I did learn something, and I verified that the video generation circuity was good.
Once again, back to trying to get the Wells-Gardner monitor to work, now that I knew the video generation circuitry worked on the Pac board, I needed to focus on the interface board. In another fit of brilliance, I remembered that I have a Millipede, which happens to use a W-G K4600-series monitor as well. I pulled the back off of the cabinet and discovered that it also uses a negative composite sync! I plugged my questionable interface board into the Millipede, fired it up, and lo and behold, it worked too. Crap!
Now I've determined that the Pac board, and my video interface board are fine. So what the hell? After a bit more thought, it began to dawn on me that maybe that Electrohome G07 monitor was, in fact, a vertical monitor rather than a horizontal one. In digging around a bit more on the Internet and getting a better understanding of clocking out pixels, I'm convinced that this is my problem. I'm clocking out a signal expecting a resolution of 224 x 256into a monitor that has 256 x 224. No wonder I can't get a good picture!
Oh well, so much for my W-G swap. It looks like I'll have to get that Electrohome working... Besides, the bracket wasn't going to work with the W-G.
I did do a little more troubleshooting with the G07 (burning out a couple of fuses in the process). At first I thought the issue was the degaussing coil, but disconnecting it didn't fix the problem. Right now, I'm looking on eBay for the shortcut - just pick up another mainboard for the G07.
Earlier in the week, I had gotten the bright idea of pulling a Wells Gardner K4600 monitor from a Defender off the shelf and testing with the Pac. The perceptive reader may note that Ms. Pac/Pac-Man is a vertical game and Defender is a horizontal game. Well, the Electrohome monitor that's in the game appears to be of horizontal orientation, so I thought I would be OK (more on that momentarily).
The first challenge I ran into was the fact that the interface board used in the 4601 from the Defender is designed to run off separate X and Y sync signals (positive). Pac-Man uses a negative composite signal. After a bit of thought, I ran down the the garage and pulled the video interface board out of the W-G monitor in my Galaga. Once I had everything wired up, I fired up the game. Voila! I had video. Oh. I had scrambled video. Crap.
At this point, I had two possibilities. The video generation circuitry on the Pac board might be bad, or the interface board I had pulled from the Galaga might be bad because the monitor is dead.
Once again, brilliance struck and I remembered that I have a Ms. Pac upright downstairs. Grabbing the main board out of my cocktail, I took it downstairs and plugged it into the Ms. Pac (which works, by the way). Unfortunately, while I got a clear picture, I got a clear picture of all "F's". On looking more closely at the board that was in the Ms. Pac, I discovered several hacks centered around a voltage regulator and some large diodes. After a bit of research, I happened on the fact that Midway had built voltage regulation into the Pac boards. Since my Ms. Pac had been "upgraded" to a switching power supply (which provides +5 and +12VDC), it was no longer necessary to have a bridge rectifier circuit on the board. Well, when I plugged my board from my cocktail into that harness, there was no AC voltage provided, so it couldn't initialize. Oh well. I did learn something, and I verified that the video generation circuity was good.
Once again, back to trying to get the Wells-Gardner monitor to work, now that I knew the video generation circuitry worked on the Pac board, I needed to focus on the interface board. In another fit of brilliance, I remembered that I have a Millipede, which happens to use a W-G K4600-series monitor as well. I pulled the back off of the cabinet and discovered that it also uses a negative composite sync! I plugged my questionable interface board into the Millipede, fired it up, and lo and behold, it worked too. Crap!
Now I've determined that the Pac board, and my video interface board are fine. So what the hell? After a bit more thought, it began to dawn on me that maybe that Electrohome G07 monitor was, in fact, a vertical monitor rather than a horizontal one. In digging around a bit more on the Internet and getting a better understanding of clocking out pixels, I'm convinced that this is my problem. I'm clocking out a signal expecting a resolution of 224 x 256into a monitor that has 256 x 224. No wonder I can't get a good picture!
Oh well, so much for my W-G swap. It looks like I'll have to get that Electrohome working... Besides, the bracket wasn't going to work with the W-G.
I did do a little more troubleshooting with the G07 (burning out a couple of fuses in the process). At first I thought the issue was the degaussing coil, but disconnecting it didn't fix the problem. Right now, I'm looking on eBay for the shortcut - just pick up another mainboard for the G07.
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