If you haven’t read part I yet, check it out here. In part I, I discussed the discovery of the modifications done to the transformer and power module. At first glance, I assumed that the transformer had burned up and someone added a second transformer to power the G.I. circuit. Even though the game seemed to work correctly, I couldn’t let it go out that way.
So I looked for a replacement transformer and I noticed some of them had different part numbers on them, even though the wiring appeared to be the same, none of the numbers matched the numbers on the transformer in the game. They would *probably* work but I figured, eh, why take a chance?
Sometimes I’m overly cautious, in this case I’m glad I was. I pulled a manual out to double check the transformer part number. It was then I had to do a double take of the rectifier board. The one pictured in the manual is nothing like the one in the game. I also had never seen one like it before. It has only one bridge rectifier mounted on top instead of underneath like all the other ones. It also only has one 12 pin transformer input plug instead of the typical two plugs, one 9 pin and one 6 pin. Oddly enough, the output side connectors are identical but pinned differently.
I’m thinking, “Now what?” Odds were definitely against having one on the shelf, turns out I was right, not only did we have one, we had two! One had a jumper wire on the back, so I passed on that one and chose the cleaner one. I gave it my usual treatment, a Simple Green bath and replaced the bridge, the 600ohm 10 watt resistor, the 6A diodes, and the four high voltage display power diodes. And for the last step, I reheated all the connector pins.
I just want to point out they only use this rectifier board in Gold Ball and Grand Slam, so it’s not common. As a matter-of-fact IPDB.org shows only 1750 Gold Balls produced and no production numbers for Grand Slam. I got lucky in finding one. The transformer, however, wasn’t as easy. It took a little digging to find one that was compatible.
To conclude this post, I will discuss a little about the operation. The lines that the previous tech spliced from the G.I. circuit and from the additional transformer power the zero-crossing detector. While I’m curious why the original power supply needed replacing, the tech who installed this had some idea of what they were doing. One problem I noticed was that the lights appeared dim. This was because the zero-crossing detector in the original game design provided 10 volts, the added transformer and G.I. circuit were only providing 6.
It uses the zero-crossing detector to turn the lights off. The feature lamps work by driving two bulbs with a single SCR. It uses an ”A” side and a ”B“ side, which is why there are two zero-crossing lines. It is a 20 volt center-tapped circuit providing two individual 10 volt references. If you see that two lamps are out, most likely an SCR has failed, I found this to be the case when I found two lamps out after verifying it wasn‘t the bulbs or the sockets.
Similarly, Williams WPC uses zero-crossing detection to dim the G.I. lights. Getting into the theory of zero-crossing is beyond the scope of this article, although I may delve deeper into it at a later date. The next and final Gold Ball post I will conclude with finding a replacement transformer and what was involved in making sure it was suitable and not going to blow anything up.