Now while waiting for some of my orders to come in, I turned to doing the checkout of the internals. I found a great guide for EM restoral:
So I started with the "Before Turning the Game On" section:
I had to run out to Harbor Freight to buy a multimeter (I'm slowly stocking my toolbox based on this project) for this work. I'm spoiled by high-end Fluke DMMs at work, but I settled for a reasonably cheap HF DMM with some extra alligator clips.
1. Check all fuses.
I didn't make the fuse tester from the guide (maybe if I do more games), but all of the fuses checked out with the DMM.
2. Check coil resistances.
We have a similar process at work (I work on the Mars Rovers) called Electrical Integration Procedures where we work through all power-off measurement of electrical components, so this section made sense to me. I made an expectations table to at least give me a rough estimate of what I should see; I later found similar pages, but I made mine from the schematic and parts websites. See screenshot below.
During the process, I found that the Hold Relay had a short. Apparently it's the most common coil to burn out, since it is held on the whole time the machine is on. It even looks burned out - the surrounding paper sleeve is burnt to a crisp. Sounds like I'll have to replace it.
All other coils check out, so I'm moving on.
3. Clean Plug Connectors.
Sanded the corrosion off of all of these with 400 grit sandpaper. Even if this wasn't necessary (it probably was), it was a good learning experience to learn where all the plugs where in the future where I need to disconnect plugs.
I missed/skipped cleaning the light sockets, and in retrospect this may come back to bite me.
4. Checking Switches
The guide recommended this for coin door switches, but I decided to do this for every switch. For every switch I could find (some of the bank and motor switches were too hard to easily access), I checked that the default state was correct according to the schematic and when the relay moved the switch changed the state (open to close, or vice versa). This was a good exercise in understanding the schematic and translating that to physical space. I read schematics often at work, but the formatting is pretty different and I'm used to DC power instead of AC. One additional wrinkle: the wire colors in the schematic are helpful, but in 47 years a lot of the colors have faded beyond recognition. Is that Brown-Red-Orange or Red-Yellow-White?
Along the way I found a few cases where the switch blades were bent incorrectly and weren't making correct contact, so those were adjusted with tweezers/needlenose pliers.
5. Cabinet Cleanup
Along the way, I found several loose parts in the cabinet. Most were fasteners, but I found one bakelite triangle that was totally unclear where it went. At this point, I just bagged it and hoped I would figure out where it went (spoiler: I did!).
On to the stepper motors and score coils, which deserves a separate post.
Lessons Learned:CoilMeasurements (resized).PNG
- Most DMMs don't have auto-ranging features. Make sure you pick the right range for your measurement. If you pick a resistance range too small, the circuit will register as OL, which can mislead you.
- Schematics are not physical representations. Things next to each other on the schematic may be very far apart physically, including in different segments (backbox, cabinet, playfield underside).
- The switches actuated by relays are not always near the relay in the schematic, or even the other switches on the relay. Have to look for the relay letter on switches all over the schematic. Once you start understanding the circuits, they're a little easier to find.