Friday October 20, 2017

Williams Diner Pinball - Non-working Saucer Flash Lamps

Author: Wayne Eggert
Date: 9/18/2011


Problem Description

This was a Williams Diner I bought a while ago that had non-working Saucer Cup flash lamps.  I had already fixed a number of other things on the machine, but the Saucer flash lamps remained.


Diagnosing
I checked the transistors involved in the cup saucer using the diode test on my multimeter.  The transistors seemed fine, so I started with the basics and checked continuity between the flasher and wire harness on the interconnect board.  Continuity to the harness was fine and continuity from the harness onto the board was also fine.

Finally I checked the cement resistor involved for the Saucer flash lamps and found it was reading "open" (ie. no connection).  It should have been roughly 3 ohms but read infinite.

Interconnect Board
Picture: Inside Backbox of Williams Diner.  Cement "Flash Lamp" Resistors on interconnect board are circled


Problem Resolution
There really shouldn't be a reason to measure infinite resistance across a resistor in-circuit.  So I suspected the cement resistor was bad and replaced R6 cement resistor with a brand new 5w 3ohm cement resistor.

Fixed Resistor
Picture: New 5w 3ohm resistor soldered into R6 for Saucer Flash Lamps

Now was also a good time to check the other resistor values.  The interconnect board gets most of the games wire harnesses plugged into it, so although it's a small board it's really a pain to keep installing/removing it in the machine.  I found a few of the cement resistors measured very low, almost as a short.

It took me a little while to figure out why.  Can you guess?

0 ohm Resistors
Picture: Zero ohm resistors underneath cement resistors

It looks like these had 0 ohm resistors installed from the factory that were actually beneath the cement resistors.  I don't remember for certain but I think the cement resistors appeared to be a non-factory addition.  In any case, these resistors with the 0 ohm resistors beneath them were unused in Diner.  I left them as-is figuring I might do more harm unsoldering them than just leaving them, but found it interesting none the less.


Final Thoughts
That's it!  A pretty quick repair overall and the cup flashers are now working just fine.  Also learned to watch out for zero ohm resistors hiding beneath the cement resistors on these interconnect boards.




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