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STTNG Ground Short (and Other Electrical Oddities)

Here's another one for the "always look for the simplest explanation first" file.

During the course of my STTNG Drop Target Saga, new problems seemed to keep popping up. Many of these served as distractions and red herrings that contributed to making said saga a three-week nightmare of frustration.

One of these was that, at the end of the second or third day of troubleshooting, the game suddenly developed a series of ground faults, specifically on Row 1 and Column 1 of the switch matrix. 

What. The. Hell. 

My tech was going to look into it the next time he came over, but I couldn't let it go. I was talking with a friend of mine and we were looking at what connectors or board problems might be causing it. Then, I got the bright idea to open the coin door while the playfield was down and look inside.

I actually said, "Oh, for f**k's sake" when I saw what I saw.

Turns out that the right safety bar--one of the "handles" that you use to pull the playfield out to 

raise it--was bent out of shape. When the playfield was down, it was touching all the contacts on the Buy-In Button--which, if you look at the switch matrix in the manual, is the top switch in Column 1 and the first one in Row 1. ​

I took the bar off and bent it straight. Problem solved. And, because it's now prone to bending, I make sure I bend it back every time I raise the playfield--and I wrapped it in electrical tape just to be sure it won't cause this problem again.

Again...always look for the simple solution.

While I'm on the subject of simple, silly things with easy solutions, during my search for the ground short, I opened the playfield part way and was planning to test a switch. When I turned the machine on, the left cannon started turning on its own and wouldn't stop. Even when I went into test, it just kept turning.


I was thinking, "Great. I broke something else." But it turned out that, while I thought I had the playfield sitting on the safety bars (as you would when it's partially up), I actually had it resting on the motor for the left gun which, inexplicably, was positioned by the architects of the game in such a way that it sticks down far enough to allow that to happen...and, when positioned just so, both contacts on the motor touch the metal lockdown bar mechanism, causing it to short. The problem miraculously went bye-bye as soon as I propped the playfield up properly.

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