Bally Switch Matrix Issue & Resolution

[Steve2010]

Anyone who has attempted to resolve switch matrix issues will know what great fun it is - not!  I have resolved a few of these over the years, mostly needing a replaced diode or capacitor.  I have also had an issue where a T-nut was bridging two rollover switches - that took a while to diagnose.

Over the past few days I was trying to resolve an issue on a Bally Star Trek where I had two switches appearing as stuck.  Anyway, to make a long story short, and after spending probably at least 10 hours trying to work what the heck was going on, it turned out to be what I would call a "leaky" insulator in the switch stack.  That is, one of those brown insulators that make up the stack - as per the image below.

The "leaky" insulator was sitting between the two ends of the diode, and fortunately I had some spare insulators from spare parts.  Sure enough it fixed it, but I would have never thought it would have been this.  And this was the issue in both switches.

I have posted this for anyone's benefit to keep this in mind when trouble shooting switch matrix issues.

[pinnies4me]

Wow, add that to the list of things to check.

[pinball god]

Can't really make out what's going on from the photo. Are you saying the insulator had broken somewhere and two metal parts were then touching? Unsure of your tip and would appreciate clarification as I'm sure I'll encounter it in the future

[Ballywannabe]

What I have found is that the ''crap'' that builds up on the switches over the years will combine with moisture to form a bridge strong enough to trigger a switch, particularly if it has a cap on it.  When my machines were in an uninsulated shed, and cold, damp winter air occured for a few days, some of my Ballys were unplayable!

[Steve2010]

Can't really make out what's going on from the photo. Are you saying the insulator had broken somewhere and two metal parts were then touching? Unsure of your tip and would appreciate clarification as I'm sure I'll encounter it in the future

I had included the image just to show what I meant by the brown insulators.  You wouldn't notice anything unusual just looking at it, but as Ballywannabe above said, it probably is a combination of subtle crap and moisture.

Whilst tearing my hair out trying to work out what was going on with the switch matrix, I narrowed it down that it had to be something about the switch assembly itself.  One was the standup target, as pictured, the other was a thumper bumper switch.  I was able to narrow it down by creating a dummy/separate J2 connector for the MPU, and wiring just two leads into that connector - one for the strobe and one for the return for the associated switch.  I pulled out the regular J2 connector from the MPU, and plugged in the test one.  I then unsoldered the switch assembly from the cabinet wiring, and connected the problematic switch to the test setup.  As the problem still occurred under this situation, I was confident it came down to the switch assembly itself (and not the playfield wiring or other switch issue).

With the machine in the test setup for stuck switches (ie. after pressing the red test button inside the coin door), I noticed that as I loosened the two screws which hold the switch stack together, the switch became unstuck (as noted by the digit '0' in the credit display.  Tightening the two screws caused the switch to become stuck again.  I was thinking to myself, what on earth is going on?  It took a little while, but I suspected something not right with the insulators between the metal in the switch stack.  Sure enough, changing the single insulator between the two diode connections solved the problem.  Now, tightening the two screws in the switch stack to fully tight had no issues with the switch being stuck anymore.  And this was the situation in both switches.

As mentioned, maybe the cold weather/humidity has something to do with it.  But it seems strange that it only affected these two switches, and not the umpteen others in the machine.  I think it comes down to the properties of the insulator.  Maybe over time, with crap build up etc combined with a bit of humidity causes problems.  Anyway, first time I have ever seen this happen.

[Mr Pinbologist]

Thanks heaps for posting this info, i think you may have just helped me with a problem i had been having with my KISS pin  

What I have found is that the ''crap'' that builds up on the switches over the years will combine with moisture to form a bridge strong enough to trigger a switch, particularly if it has a cap on it.  When my machines were in an uninsulated shed, and cold, damp winter air occured for a few days, some of my Ballys were unplayable!

I had this issue (still have it after a lot of rain) with my KISS, where if you started a game the right bumper would go completely ape shit, firing continuously! I too spent hours trying to track this down, even swapping boards etc all to no avail   In the end i found if i unplugged the switch matrix connector going to the CABINET switches, the game could be played (removed the connector after starting a game).  

The last time the game started acting up in this way, i got my heat gun and blew hot air into the cab while it was doing the bumper firing on its own thing.. it stopped within about ten seconds and functioned normally!! Ever since the if i wanted to play KISS and we'd had a lot of rain i'd just blow hot air into the cab   But now, armed with this info i think i'll be changing a few switches  

Btw, this NEVER happened on any of my other Bally or Stern games. They are all in the shed which i insulated as much as i could do when i moved in to the place.

Thanks again  

[goodolddays]

Very handy tip. Thanks for taking the time to post . I will be keeping this in mind for the future .

[pinball god]

funny you should mention something I think I may have on my twilight zone. the clock target is acting a little strange. it kind of gets stuck on or something and if I test it I the switch test a whole row can activate. if I move the plastic target part a little left or right while the stack remains stationary the problem goes away. move it back a little and the whole row lights up. obviously during game play this garget can either work or not depending on the type of ball strike.

could this be similar in problem and if so, is the solution replacing parts of the stack?

thanks