The Addams Family Pinball

It turns out that the problem reported in my last post regarding the intermittent fault on one pair of optos wasn’t simply solved by cleaning. In fact it didn’t matter how often I cleaned the opto pair, the fault would repeatedly come back – but not permanently. Time to investigate….

On taking the necessary opto apart I was horified to discover a lead which had never been soldered. This means that this pinball machine has had this intermittent fault since its birth:

Source of an intermittent problem

I’ve been suspecting an issue with my STTNG lately. It started off with having a game with two balls in play. Then there was a game where the machine appeared to be searching for balls as it tried to load the left cannon. Then this evening, Final Frontier finished even though I still had two balls on the playfield. Once the balls had drained and the machine tried to set up the playfield for the start of the following game, it only sent two balls instead of the usual three to be loaded under the playfield. Obviously the computer thought there were three balls under the playfield when there were actually only two.

On clearing the balls out from the machine (using the routine in the menu) it was apparent a ball hadn’t been staged in the pop-up for the left cannon. Sure enough, on checking the switch matrix, the relevant opto switch for the pop-up was registering closed, meaning the machine thought that there was a ball there, when there actually wasn’t.

So I got out a cotton bud and soaked it in alcohol to clean the opto switch pair and everything was as right as rain again.

An easy fix for a most annoying problem!

Having played my ST:TNG now for quite a while, it has become ever increasingly more annoying that the pinball sometimes becomes trapped behind a hanging ramp switch on the Alpha Ramp. The only way to get this stuck ball out is by removing the glass and physically taking it out. The problem here is that the switch has been replaced with the incorrect switch with an incorrect actuator.

Having acquired a new switch (second hand) from a forum memeber on my favourite forum (flippermarkt.de) I proceeded to replace the existing one. And what I found was an interesting hack. The switch had been replaced (with the incorrect switch) and the leads had been simply twisted together and covered in normal sticky tape:

Sticky tape used instead of insulating tape....

... covering twist connected leads

Yeuch!

The original display that had come with my ST:TNG had already started gassing at the bottom right of the display:

Display with gassed out region bottom right

Although this isn’t too noticable and actually during gameplay not noticable at all, I was able to sell it to another pinhead today (at a knock down price) and replace it with a newly acquired one.

I notice some ramp damage today on the subway ramp under the playfield where balls falls into the ramp once the single drop target has dropped. So I decided to take off the ramp to repair it. Although I had read many horror stories regarding the removal of this ramp, it turned out to be not so bad.

Main subway ramp

Of course the ramp was filthy, so I cleaned it with Bref prior to repairing the cracked ramp with Ambroid Pro Weld (an excellent soltuion for repairing ramps, as it welds the cracked plastic together at a molecular level rather than sticking them together).

Having put everything back together, replacing J121 in the process and inserting some new batteries, I turned the machine on and was met by some crazy canons which seemed to have a mind of their own and just kept on rotating. Fortunately I was prepared for this (having read up on the most common problems with a ST:TNG) and knew that if the opto in the canon wasn’t working (which it wasn’t on the left) that there was probably a wire harness problem. So, having removed the left canon covering, the opto pair and unplugged the wires from under the playfield, I removed the wiring harness to reveal some very damaged wires:

Broken wires from the wire harness from left cannon

So, having repaired these and put everything back together, I had a fully working ST:TNG. Wonderful!!

My recently acquired ST:TNG came under scrutiny today. The backbox had already been removed, so it was a case of checking out the PCBs. Two things were immediately obvious – a scorched J121 and an external battery wired directly to the battery holder on the CPU board.

Inside the backbox - note external battery bottom left

Although dirty, the condition of the boards was good, so I just had to clean them up with Bref.