If you ever have a display whose segments and/or digits are "flickering/dancing", this may be of assistance to you.
One of my Bally displays was playing up. It was sporadic at first, but then became consistent. This was a 7 digit display on Skateball.
The problem was that both of the comma segments, and most of the segments in the 100,000 digit began to "dance/flicker". That is, the brightness within the segment would "dance" in a random way. This occurred when these segments should have not been lit, and even when they were lit when they should have been, the "dancing/flickering" effect could still be seen within the segment.
Although a video clip would have been better, here is an image of the problem.
As usual, the first place to read was Clay's guide. At first I thought to swap the display to another player position, but the problem persisted - problem must be with the display board. Then maybe it was some bad header pin connections, so I reflowed the pins on both the J1 and J2 connections. No improvement.
I then thought it must be something faulty with one of the transistors. As both comma segments were mucking up, I thought it must have something to do with at least that particular segment driver. Eventually, I tested every transistor - all OK. Check all the resistors - all OK. Swapped the BCD to 7 Digit Chip with a known good one .... problem still there. This was driving me crazy .... what could it be?
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In between all the checking above, there were many weeks that passed. After testing something for a while, I would say "enough is enough, leave it for another night".
So, quite a few months had now passed. Another one of those nights presented itself, I thought, time to try again. Don't know what lead me to it, but I tested the actual voltages on the pins leading up to the glass display itself (J2). The voltage readings on the pins associated with the segment drivers were much higher than they should have been. Now what ....... what the heck is going on! Well, I tested the voltage on either side of zener diode VR1, and got the same reading on either side (ie. both sides were 170V - the HV voltage). So, VR1 was shorted, and this zener usually drops the voltage 110 volts.
This image of the board shows VR1 at the very right side of the display board. Six digit displays also have this diode.
So, a few replacement diodes were added to a very large list of other (unrelated) things to order from GPE. I received that package the other day, and today replaced the diode. Into the machine she went, and voila, all is good.
Image of the board with the new diode VR1. Note that the replacement diode from GPE was much chunkier than the replaced one, and just fit within the existing board design.
Working display image.
Interesting to note that Clay's guide did not cover this situation. That's cool, I don't expect it to cover all situations. But persistance paid off!
