Gorf was always one of my favorite arcade games because it included five different games in one. Also, it included speech and two audio channels. I liked the joystick with the trigger and that it was centered so I could play with either hand. I often played for so long that my hand and arm would get tired so I had to keep switching hands.

I had been looking for this game for about 14 months during which time I saw several. All of them were converted or stripped or in very bad shape. I didn't feel like another total-project job so I just kept waiting. I finally lucked out when I got this one. It was in very good shape and it sold dirt cheap so I couldn't pass on it.

Just look at how nice this control panel. Usually all of the text is worn off and the metal looks awful. This one looks practically new.

Gorf is very well illuminated with 2 bulbs in the upper marquee, 2 in the lower marquee, and 1 behind the blue panel above the screen. When my machine was delivered to my home, some of the old lamps (I call them fish-tank lamps) had fallen out of the sockets but luckily none had broken. I removed them all anyway and installed 9W compact fluorescent bulbs because these will look better, run cooler, and last a lot longer. This picture exagerates the light output a bit but it certainly is the brightest of all 12 of my games.

As luck would have it, this machine wasn't working perfectly as advertised when I received it. Besides a few loose connections (caused by aged connectors), the video color red was missing and the width (top to bottom in this case) of the picture was way to big so that the text was going off of the top of the screen. The width was easily dialed in but the red proved more difficult to restore.

First I tried to find the R signal at the RGB inputs on the monitor using my scope. The B & G were there but no R. I followed the R wire back and it went into a small board mounted on the side of the cabinet. Checking the schematics, I learn that this board is called the "interface" board. What's this thing supposed to do?

Gorf has 6 circuit boards sitting in a metal rack in the bottom of the cabinet. The boards are connected to each other by a single "backplane" board that has sockets for all of the boards. Gorf video originates on the CPU board in the form of three signals called R-Y, B-Y, and video. These signals are digital and come from a 40-pin custom AMI chip. Each of the 3 signals controls a PNP transistor (Motorola MPSH69). These transistors are very fast. They are rated for 2 GHz and that's a lot faster than your average general purpose device. The outputs of the 3 transistors exit the CPU board and, through the backplane, travel to the game logic board. Here, the signals each control an NPN transistor which produces an output by driving a 100 ohm resistor. The final R-Y, B-Y, and Video output signals then go to the interface board.

The interface board is an op-amp mixer circuit that converts R-Y, B-Y, and Video signals into R/G/B and Sync signals, and these are the signals that finally go to the monitor.

In my case, my scope showed that there was no R-Y signal going into the interface board so I followed it back to the game logic board. There I found that the 100 ohm resistor (R68) was fried. The NPN drive transistor (Q7) was okay according to a quick diode-test check. I replaced R68 and tried the game again. My screen had red again but unfortunately there was way too much of it. The red was obviously stuck full on. Okay, so I followed the R-Y signal path back to the CPU board. There I found the MPSH69 PNP transistor (another Q7) was broken in half.

I replaced it with a general purpose part (MPSA06 rated 100 MHz) and the results were awful. Control of red was restored, but because the transistor was so slow, the video was terribly smeared. It looked really bad. In fact, it was so bad that I quickly decided that no red was much better than smeared everything so I removed the transistor and waited until I was able to get the proper part to install. Trust me, it was well worth the wait. The reason that it smeared everything and not just red is because the R-Y signal must be combined with the B-Y signal in the interface board to generate R/G/B. Anything that effects either of these signals ultimately effects all 3 of the final colors.

An aside here, Gorf has three small boards that are mounted separately in the machine (display interface, joystick, and display driver). If you find yourself looking for a complete set of boards for Gorf (or Wizard of Wor), be aware that most listings sell the 6 main boards in the metal rack and usually do not include the other 3 small boards. Also, be aware that the metal rack is absolutely required to make the 6 main boards work because the rack has the backplane in it.

I like the joystick in Gorf better than many other games because it uses an optical pickup system. There are no leaf switches to adjust or wear out and no microswitches to make noise. This circuitry is on the circuit board mounted directly under the stick.

Another little thing that I like about Gorf is the small panel to the right of the screen that has 6 difficulty level indicator lights. These lights are driven by the "display" board. Each time you make it through all 5 games, you are promoted to the next level of difficulty. Each lamp in the display board lights one of the 6 squares labeled Space Cadet, Space Captain, Space Colonel, Space General, Space Warrior, Space Avenger. Once you get to Avenger, the game doesn't get any harder so if you are proficient at this level, you can play for as long as you can stand it. The display board also drives the small lamps inside the top of the joystick.

 

Power Regulator Board After Rebuild: (click images to enlarge)

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Midway, 1981