Hello,
I am relatively new to the EM machine restoration hobby. I am currently on restoring my 4th machine. I am concentrating on EM shuffle alley machines (1950-60s). I find the machines on Craig’s list in non-working condition. I then fix them up and pass them on to friends or siblings for the cost of the machine and materials. My paying job is a Technical Support Engineer for BMW of North America. So far I have been able to fix all the issues on all the machines I have purchased except this one. The current one that I am working on is going to be a wedding present for my younger brother and it has one issue that I am unable to fix. I am hoping someone here will take pity on me and help me out. The machine is a 1968 United/Williams Delta shuffle alley machine. It was purchased in non-working condition and had not worked in years according to the previous owner. The issue I have is that intermittently the #10, #6 and #2 pin coil latch plates will not stay engaged/locked after the main reset relay bar is activated. Prior to working on this issue I have gone through the systematic approach as described in pinrepair.com. I have already gone through all the Step up Units to insure they functioned properly and cleaned out and renewed all the old gummed up grease. I have also checked all the switch adjustments on the machine (only found 3-4 that needed slight attention). I cleaned all the contact boards with a red scotch bright pad and put a light coating of Super Lube Synthetic Grease. I have also disassembled all the score wheels, cleaned of the old grease and reassembled without grease (metal to nylon contact = no grease needed). This fixed all the issues I had except the last one. The last issue I have is that intermittently the #10, #6 and #2 pin coil latch plates will not stay engaged/locked after the main reset relay bar is activated. This happens intermittently and can happen to one, two or all three randomly. It happens most frequently to #10 (once every 3-4 resets on average). #6 is next (once every 4-5th reset). #2 happen once every 20-30 resets. So far I have done the following to address this issue with no success:
Removed main reset bar, welded up elongated holes and re-drilled new holes in the proper location. Welded up and reshaped excessively worn stud on pivot bar that connects main reset plunger to main reset bar. Ensured that the main reset bar has enough travel and moves freely to reset coils properly. Insured main reset solenoid pulls plunger in far enough to activate main reset bay far enough to reset switch plates. Rechecked adjustment of all switches on Main reset assembly. Rechecked switch adjustment of all playfield contact switches. Rechecked all switch adjustments of pin tip up coil switches. Measured resistance of all coils on reset bar. All coils except the #1 coil were between 13.2-13.6Ohms (S-29 950 Light Blue in color). #1 coil measured at 5.4ohm (S-27 750 Green in color). I can see no reason why this coil should be different and the solder joint makes me think it was replaced sometime in the past. At this point I did not think the difference is significate enough to cause and issue and moved on.
I had someone else shoot the puck while I watched the main reset in action and I found that the coil plate for the #10. #6 and #2 pins would intermittently momentary lock in place and then seem to slip back out and not stay engaged. So the problem was that the coil would activate, the latch plate would engage but then immediately disengage causing my issue. I then removed the #10 coil, latch plate and switch plate and inspected them for excessive wear or damage. Finding no damage with the components I reassembled them and then connected a compact florescent light bulb using alligator clips in a parallel circuit with the #10 coil at the coil connectors. I continued testing and found that when the coil worked properly the light would flash momentarily when the coil was activated and did not flash during the main reset operation. When the problem would occur the light would flash immediately following the main reset bar activation. This was an indication that I was getting a second voltage signal being sent to the coil releasing the coil plate immediately after the reset. Occasionally the light would flash dimly during the main reset activation but would not release the coil plate. This tells me that the voltage signal this time was not strong enough to activate the coil. This testing with the LED light was also done to the #6 and #2 coils with the same results. So the million dollar question is; what can be causing the secondary pulse causing the coil to activate and release/disengage the plate?? As a side note, when manually releasing the coil plates and then activating the roll over relay I was never able to get the issue to occur. It seems that you need to shoot the puck to get the pins to pop up for the issue to occur. I have attached pictures of the machine, Main reset assembly and a close up of #10, #6 and #2 coil plates in the released/disengaged position. I have the wiring diagram, playfield switch diagram and additional documents describing the switch and relay operation.
I thank you in advance for any help you may give.
John

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Wow- thanks for the quick and varied replies.
I will answer the questions in order I received them:
Mopar:
I have cleaned and lubed the reset bar with no change. I have tightened the switch stacks but I will go through them again. With as many as there are I might have missed one.
I have adjusted the switches on the bank relay twice already without success but I will inspect them again. I like the tapping idea- I will defiantly try that.
Yes I checked the roll over switches twice but I did this with the playfield upside down on saw horses and now I am afraid that the weight of the roll over wire may be causing the switch adjustment to be too close when putting the playfield in the correct position. It’s very had to see/set them from underneath. I will have to make up some kind of short table so that I can comfortably inspect them and adjust them again. I also found another port where someone found a switch stack spacer cracked and shorting so that is something else I will need to check.
When you state that I may have magnetic plates: is there any easy way to check them? I touched them with a small metal rod but it had no attraction to the plates. Do I just swap plates with another pin coil that is not having and issue to see if the problem moves?

Dr of Style:
Yes the reset works properly and the locking tab is completely hidden. Then the plate will release just a split second later.
The # 1 coil has lower resistance so it would in theory have more current flow at the same voltage and pull in the latch plate faster. It would also create a larger magnetic field than the other coils. I am not sure this would affect the operation. Are all the coils for all the pins supposed to be the same? I will order one soon.

Drmsmd:
I already tried swapping the #10 latch plate and switch plate spring with #3 (no change). The # 3 springs are of the same vintage as the rest so they may be too week as you suggested. Any Idea where I can get good quality replacement springs?

My homework:
Using the schematic follow the # 2, 8 and 10 coil trip line back to what all is in line with it. Look for common element.
Recheck all game step units.
Inspect them and adjust roll over switches when orientated in the correct position (not upside down). Check for switch stack spacers cracked or damaged causing a short.
Check switches in the relay bank to see if one or more is slightly too close and touching from the reset's vibration. I will try tapping on switch bank assembly in various places to see if problem reoccurs.
Swap # 10 latch plate with another known good number in case it is Magnetic.
Replace # 1 coil with the correct coil.
Replace latch plate springs on # 2, 6 and 10.