Troubleshooting a dead Williams System 3-7 logic board

Troubleshooting a dead or locked up Williams System 3-7 logic board. 

Here is a basic intro to fixing your locked up logic board. I’ll assume you have a good working power supply and all your voltages are present. First you should check your diagnostic LEDs and see if they are trying to tell you anything. Sometimes just reseating connectors and pressing the socketed chips back in will help get things going. Some of these games have been around for 4 decades or more and will need a few routine things to keep them reliable. 

If the diagnostic LEDs aren’t telling you anything, or the board appears completely dead try changing the CPU or if its giving you inconsistent information try swapping out the driver board, if you have access to one. I’ve had a few instances myself where I chased around a logic board issue that was caused by the driver board. Typically it seems the switch matrix PIA is the culprit, but any one of them really can prevent the logic from starting. Also the PIA on the board itself can cause a lockup condition too but I haven’t encountered that very often. 

Any experienced tech will tell you that you’ll spend 90% of your time finding out what isn’t the problem. The reality of it is that a lot of the time problems can be fixed by swapping a known good part for a suspected faulty one. Not exactly a sexy way to fix your games but it works, which can be helpful if you don’t have access to tools like a scope. 

Assuming extensive acid damage isn’t an issue there’s a few things that need to be done to make sure you have a solid foundation before getting into the fancy stuff. All IC sockets need to be replaced and the 40 pin header on the driver board as well. I can’t tell you how many times I’ve brought boards back to life just by changing the IC sockets. 

As a side note, I really dislike the round .156 pins on the board and I will typically replace them with new square ones and install trifurcon pins on the wiring. This isnt always necessary unless you are experiencing problems like erratic displays, switches, lamps or coils. If you are just doing a quick repair, or don’t have any plans to keep the game you can get away with skipping this step unless it’s the obvious cause of a problem. 

It helps to have some good tools, a digital multi-meter and a logic probe for the most part will be sufficient. A logic probe will be handy for observing the reset circuit as well as some other lines to check for activity. You can also use it to check for clock pulses. It won’t tell you if it’s running at the right frequency but at least you’ll know if it’s pulsing or stuck either high or low.

The reset circuits main job is to prevent the CPU from starting for a few hundred milliseconds or so till all the voltages stabilize. Think of it as a time delay. While observing it you should notice it go from low to high while turning the game on. A typical CPU reset is an “active low” function meaning that when the reset pin is taken low, or shorted to ground, the CPU will reset. If you ever noticed the word “reset” with a bar or line over it, that’s what that means. That’s also true for any function listed in schematics or documentation with a bar over the word. It means it’s an “active low” function. 

If the reset circuit isn’t functioning correctly then you’ll need to dig into that before going any further. If it is and having already changing the aforementioned sockets and driver board interconnect headers doesn’t get you any results the next item to swap out would be the ROMs themselves. Unfortunately the old masked ROMs don’t hold up anymore and a new set may be in order. You can get the necessary ROM files from www.planetarypinball.com if you have access to a ROM burner or you will have to buy or borrow a set from someone. Some of the game ROM files have been combined to reduce the number of chips used for certain games. Depending on which system you have, modifications to your board may be necessary to accommodate changes to the ROMs. That is beyond the scope of this basic troubleshooting guide and I’ll get into board mods at a later time. 

Even though this article is intended for Williams systems 3 -7, it really applies to just about any pinball logic board since the same principles apply. Hopefully you gained some insight on how to deal with dead or locked up boards, check back for more troubleshooting tips and helpful info.  

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