Tracking down drop targets that won’t reset – Bally-35 “Mystic”

This is a game that’s been sitting in the back for awhile at my place that I keep meaning to get to, so I finally jumped back into to figure out what was wrong. It’s weird to go over notes you made 6+ months ago and try to pick back up where you left off — remind me not to do that.. LOL But the issue was relatively simple: The center bank of drop targets was not resetting.

In this series of videos, I go over, step-by-step the process of how to figure out what’s causing this problem, how to read schematics and manual diagrams, and the various points of failure, and once again, we are reminded of “Ockham’s Razor” which suggests the most obvious cause is the most likely… OR IS IT?

Interestingly enough, once I figured out where the problem was, rather than solve it the traditional way, I choose to do a “hack”… basically just to see if I could do it. The choice was, do you replace an entire 16-pin IC that’s only using one small part of it (involving adding a socket and a new chip that is pretty expensive and hard to find) or do you “hack” the damaged chip and piggyback a new component on top of it? Normally I don’t do these kinds of MacGuyver stuff on system boards, but it was a fun trick to try and it cost a few cents and about 10 minutes verses a lot more time than would have been used to replace a whole IC.

One reason why this hack job is particularly sloppy is because I had to work on the board in the game due to the previous owner having hard-soldered some wires to one of the connectors – that’ll be another future project to clean up all that mess, but for now, I needed to get this back working.

To understand what I did, here is a substitute circuit board showing the position of various individual 2N4401 transistors overlaid on the CA3081 IC package. Using this you can figure out where to insert a transistor manually on the IC pinouts if one of them fails:

How to test bridge rectifiers (in pinball machines and elsewhere)

The other day I was working on a game and traced the problem back to a blown bridge rectifier, so I thought it might be nice to produce a short little video on how to test/check bridge rectifiers in pinball machines, as well as a little info on what they do.

Diagnosing problems with Mist Multiball mechanism on Bram Stoker’s Dracula

Diagnosing problems with the mist multi-ball assembly on a Bally/WMS Bram Stoker’s Dracula pinball machine. In this case, we were not getting power to the motor, which is supplied from the 20vdc circuit on the power driver board (which also powers the flash lamps). In this series of videos I show how to test the mist motor, and where you check for power and back-trace it to the driver board, then identify which components are related to this problem and how to fix it.

Building replacement LED displays (from a kit)

This is a fun series of videos of me trying something new. Let’s replace the old gas plasma displays in a Bally 35 solid state pinball machine with new low-voltage LED displays. This reduces the power consumption of the pinball machine and cuts out the high power portion of the power supply board for the display – a whole area we don’t have to worry about any more by switching over to LEDs. The price for this as a kit is quite reasonable (and cheaper than replacing them with used displays usually). But it takes some time and skill to populate your own circuit boards. I’m going to give it a try. Let’s see how it goes!

Here is a time lapse of me doing the lion’s share of the board work:

And here’s the finished product!

Upgrading eddy/proximity sensors on Bally/WMS games (Theater of Magic)

Recently I decided to replace the trunk eddy sensor on Theater of Magic with something more reliable than the original Bally/Williams proximity sensors. They are prone to “drifting” and will need regular adjustment. There’s a company that makes an auto-adjusting board that I wanted to try out, so here is my video showing the installation of that new board. This should make the game a little bit more reliable.

Dignosing and fixing a dead WPC MPU board (with RAM upgrade)

In this video series, I am working on a client’s “Dr. Who” pinball machine that wouldn’t boot up. It was just dead. None of the diagnostic LED blinks would blink on the WPC-89 MPU board, so I go over the process of how to identify and isolate the problem, then I upgrade the board with NVRAM (non-volatile memory) so that it will never need batteries again.