A little pinball tech : G.I. lights at coin door fix on WPC-S system

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Dave W.
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Joined: Sun Dec 12, 2010 11:20 pm
Location: Montreal (Ile Perrot)

A little pinball tech : G.I. lights at coin door fix on WPC-S system

Postby Dave W. » Wed Jan 17, 2018 8:38 pm

For starters, I'm no whiz with pinball repairs. But I take the time to research things when I have problems and just wanted to share a recent fix I did. I love Sparky's recent tech postings and think they make great use of MAACA.

Problem : Coin door G.I. lights not working
System : Bally WPC-S (World Cup Soccer 94)

So this is usually a simple fix, right... change the bulbs and you're good to go. Well, not in this case. New bulbs installed and still no coin door lights.
I grounded an alligator clip to the frame of the cabinet and connected the other end to the G.I. return wire on the socket... the coin door lights came on. So voltage is good but there is a bad connection somewhere.
ground coin door.jpg

So let's follow this purple wire (G.I. return) as far back as necessary.
With meter set to continuity, I confirmed that the signal from the bulb socket to the coin door interface board was good

If i look at the schematics of the coin door interface board, the coin door G.I. goes from J5 (pins 1,2) to J2 (pins 3 and 5).

From J2 at the coin interface board, the G.I. then connects to J119 (pins 1, 3) at the power driver board.
j119.jpg (7.49 KiB) Viewed 193 times

So, I checked continuity from the coin door interface board all the way up to the plug at the power driver board. Checks OK. Let's keep going...

Looking at the layout of the power driver board, you can see that the solid purple G.I. return at J119 (pin 3) gets its signal from J121 (pin 6). Checked continuity between these 2 points and nothing, I get an open connection. So I've likely got a broken trace or bad solder joint.

Pulled the power driver board off and inspected the area. The trace on the top side of the board looked fine and the solder joints looked OK too. At this point, I was tempted to just run a jumper wire from another source to J119-3, but figured I'd do it properly.

Removed the J121 header pins and the solder pad on the top side of pin 6 looked pretty worn. Pretty sure this was the problem. The signal comes from pin 6 at J120 to pin 6 at J121 on the bottom side of the board and then travels to pin 3 at J119 on the top side of the board. I just needed to recreate a proper connection between the plated through-hole at J121-6.

I made a little stitch from 4 strands of copper wire, lightly soldered it through the plated through-hole at J121-6, essentially joining the 2 solder pads together. Popped a new header pin in place. Even without solder, I was already getting continuity between J119-3 and J121-6, so I knew this fixed it. Soldered the pins in place, reconnected the board, and voilà.

Seems like a lot of work for coin door lights eh?
lights on.jpg

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Re: A little pinball tech : G.I. lights at coin door fix on WPC-S system

Postby MIkea » Sat Jan 27, 2018 2:20 pm

This is great!
Thanks and keep ‘em coming!

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