Do not attempt to replicate what I demonstrate in the post below.
High risk of electric shock!
You have been warned!
This story started a long time ago. Like late 2014. I was fixing a United Singapore bingo machine. Everything was going well. The machine was ON and plugged in. Then, I touched the trip bank assembly reset arm and got a shock. Nothing dramatic but it was quite a zing.
I immediately suspected the large 120V reset coil, something like the coil's winding was shorting to the brass sleeve.
Back then I only had a crappy multimeter that didn't go into the megohm range.
Heck! It didn't even go that deep into the kiloohm range so when I measured between the winding and the brass sleeve, it measured open circuit. So based on my dodgy measurement device with a very limited range, the coil tested OK. Seemed fishy and I suspected the multimeted wasnt sensitive enough.
Fortunately, I had a spare coil, swapped it out, and no more getting zapped by the trip bank reset arm.
A few weeks ago I remembered the incident with the Singapore coil and it got me thinking. It piqued my curiosity. I looked through my pile of bad parts and found the bad coil in question (shown above).
I ordered a Chinese Megohmmeter off ebay, I think it was the lowest priced one for sale. I tested the coil with the Megohmmeter... 0.034 Megohms
Be
careful when using a Megohmmeter. You can literally zap yourself with the probes!
Then I tested it with my current multimeter... 0.23 Megohms! There's like a factor of 10 difference between both measurements. Anyway, the coil is bad. That's an established fact. Good coils should measure open circuit between on of the lugs and the brass sleeve.
Then to illustrate just how bad the coil is: I put 120V on one of the coil lugs and measured between the bracket and ground... 119V. No wonder I got zapped all those years ago!
Never play with line voltage! I'm demonstrating this so you don't have too.
When working on old games with coils with brass sleeves, that's something to consider. The risk of getting zapped! The coil winding might be shorting to the brass sleeve and then conduct to whatever metal part the coil stop is in contact with.
The enameled wire might be damaged either from heat or wear. From factory there's a kind of cardboard insulator at the core between the sleeve and the winding but if the coil was re-wound, or if the coil got too hot at some point, that insulator might not be there anymore or may be ineffective.
So the moral of the story is if you want to fix old pinball / arcade / bingo machines buy a good multimeter. With the especially old coils test the resistance between the winding and the sleeve.
