I have a 1975 Williams which the match unit armature sticks to the coil.

I have come to my wits end, I have no idea what is causing this. The coil is pulsed on, pulling the armature to it. Power is removed from the magnet and the armature remains stuck to the coil pole.

I can reach around with my finger and with just a very slight touch on the backside of the armature and it pops loose from the magnet pole. It's like the armature has sticky adhesive on its back side.

I've disassembled this unit 3 times, cleaned the armature backside and coil end-pole with alcohol and gave it a light sanding. The last time I reassembled it, I increased the return spring pressure and it worked properly for maybe 30 games or so and it's back sticking as shown in the video.

I have also tried adding various width shims (washers) between the coil and match unit frame, where it mounts.

The first thought is it may be hanging up on the ratchet, but you can see I can slowly rotate the ratchet shaft, even clicking the pawl which shows it is not a mechanical ratchet bind.

The first part of the video-
I rigged a yellow wire clip which I connect to the 24v buss for testing. You'll see me start a game and activate the relay- then release it with my finger.

The second part of the video-
I thought maybe something was keeping the coil energized so I rigged a 24v lamp and clipped it onto the coil terminals. It shows nothing is keeping the coil energized and rotation of the ratchet shaft.

Any ideas at all? I am dumbfounded and I need to get this fixed.

Thanks in advance.

match-unit.jpg

Thank you, both of you.

I've been very busy before having the chance to read your replies.

I had the unit apart once again...I had really polished both contacting surfaces of the armature and coil pole. #320 sand paper, graduated down to #1000 then mirrored with #0000 steel wool.

You both are right, and it still stuck just as bad. There is residual magnetism left in the coil pole as you say, I can feel it trying to stick even with the game powered off.

I fully and 100% accept the solution you both offer and not questioning it.

But there's something I don't understand about this, and that's the fact these are AC coils. I can understand how the poles can become magnetized with a DC coil but not these... Yet these AC coils obviously do.

I guess it has something to do with the brass insert at the tip of the pole? I know the brass shader eliminates armature chatter caused by the AC, as it holds the magnetism between cycles.

My own flawed logic would say that introducing an AC field from a demagnetizer to the pole should be the same as applying AC to the coil itself... That there would be no difference between applying AC to the coil and applying a demagnetizer.

Maybe there's a difference between applying the AC field to the end of the pole versus in the middle of it. Maybe, I'm not sure.

But thanks again for the replies. I'll take your advice to heart and give it a try.

Well, I dedicated almost all day to resolving this issue, and I think it's fixed.

I disassembled the match unit and demagnetized the coil's iron core, the armature and the steel frame. I put it together and by manually operating it with my finger, I felt no sticking or attraction at all.

So I powered up the game and it stuck on the first pulse. Afterward I worked it again with my finger and the magnetic "stick" had returned.

Back to square one. Things just didn't make sense so I thought about this a bit deeper.

Why would the factory use a brass screw to mount the coil? There's a steel lock washer under the screw, then a thick brass washer which goes against the steel frame. The only reason I could think is to magnetically isolate the coil's iron core from the steel frame.

If that is so, I am screwing it together so the coil's iron core is flat against the frame. Maybe this is setting up the mysterious magnetic field?

I found a suitable brass flat washer in my stock and put it in. Although it was already very thin, it wasn't thin enough to allow enough clearance for the ratchet to operate. I took the washer out again and reduced its thickness first with a bench grinder then finished it up with a flat file to make it about the same thickness as the cardboard of a cereal box.

I demagnetized everything again then put it all together. I've played back to back 4 player games for about an hour now and it is working every time.

Looks like this was caused by a missing brass washer under the coil... Shown in red on my diagram.

Diagram.jpg