Beautiful diagram Rolf and Welcome! Thanks for posting it. I want you to know how sad I was when I heard of your medical issues. I am heartened to see you back in the game and posting again.
We seem to have, independently, come up with similar solutions.
Quoted from Pecos:
Problem: A lamp is flickering on a 1975 Bally Wizard! playfield. Another appears to be dead, even after testing the lamp and finding it to be good. Yet another goes from dim to off. What are the points of failure on a lamp socket and how do you remedy them?
Quoted from RocketFromTombs:
Corrosion (dull grey) on the outer socket or on the center nub. Poor connection between center nub and the tab that the wires attach to. Weak spring on center nub, or fatigued metal not securely holding the lamp if you have those cheap style sockets...
All good answers. I forgot about a weak spring and not securely holding the lamp answers so you get extra bonus points!
Quoted from Cheddar:
I watched a tech at the MoP in Banning solder buttons to tabs and barrels to mounts on an old em. He pulled the playfield and did all.of them at once. Machine lit up bright and beautiful after that.
This is an alternate solution that I don't like, but may be perfect for you. There is almost always more than one way to fix a problem and if you like the solder method, gopher it!
Quoted from Stoomer:
First attempt: Twist the metal tab the wire attaches to - this tightens up the connection between the plate and the socket itself, and often is enough for it to work fine after that.
Second attempt(s): Solder the socket to the base as Cheddar describes, and/or resolder wire from tab to nub on the underside of the socket
Third attempt: Replace socket
I forgot about the solution of last resort, replace the lamp socket! I have done this more than once. Bonus points for a solution that I had forgotten about.
Cleaning the lamp and lamp socket is the solution for oxidized metal. Perhaps you have seen this oxidation. It is a white coating on the lamp socket and is the enemy of proper electrical connections. There can also be corrosion and dirt, your basic 'grunge', on the connection points.
I use 91% Isopropyl alcohol and nicovolta's Magic Brush. The Magic Brush is a Dremel tool and a #443 wire brush and it is the best method I have found for cleaning corroded and oxidized EM parts.
First, use a Q-Tip soaked in Isopropyl alcohol to clean. Then use the Magic brush to polish. Then, again use a Q-Tip and Isopropyl alcohol but drier this time. I am going to call this the IPI cleaning method, Isopropyl, Polish and Isopropyl.
Lamp Socket Points of Failure Bottom (resized).png
Lamp Socket Failure Points Top (resized).png
Connection points 2, 3, 4 and 5 get the IPI treatment. Point 2 is best cleaned by pushing down on the lamp socket 'center post,' (still need the name of these parts), just as Rolf shows.
I used a little bit of solder wire, tightly tied, as a last resort if the connection was still bad, but a good polishing should give you a good electrical connection. If you must use a wire, Rolf's copper wire is a much better solution than solder wire. Solder wire melts too easily and is too 'fat!' Like you Rolf, I do NOT like using solder on my lamp sockets.
I was working on a Capt. Fantastic and The Brown Dirt Cowboy when I discovered that the lamp contacts were badly oxidized, a good reason why most of these bonus lamps weren't lighting. I usually just replace all lamps with new lamps, so I had not seen this problem before. A quick polishing of connection points 3 solved the problem.
The Harlem Globetrotters On Tour I was restoring had a 'dead' lamp on the GI lamps. After a lot of consternation, I discovered that the 'from transformer - hot?' 6 Volt wires had been soldered to BOTH points 1 and 6! Electricity will not flow through that type of connection!
Here is a summary of how to fix the six failure points on a lamp and lamp socket:
Connection Point 1: Look for loose wires. Check to make sure there is a solid solder joint. Verify that the 'from transformer' 6 Volt AC wire is connected and NOT the 'to transformer - neutral?' usually bare wire. Please, someone, correct me if I have those wire names wrong.
Connection Points 2, 3, 4 and 5: Gets the Q-Tip soaked in Isopropyl alcohol, Magic Brush to polish and Q-Tip and Isopropyl alcohol, (IPI), treatment. Be sure to thoroughly clean and polish connection points 4 where the bayonet nubs attach to the socket! This point of electrical connection is often overlooked but just as important as the other connection points.
Lamp Socket Oxidation (resized).png
Filthy exploded lamp socket parts.jpg
Just look at all of the corrosion and oxidation on these lamp socket parts! After you are done with IPI cleaning, these parts should be gleaming!
Connection Point 6: Similar to Connection Point 1. Look for loose wires. Check to make sure there is a solid solder joint. Verify that the 'to transformer - neutral?' 6 Volt AC usually bare wire is connected and NOT the 'from transformer - hot?' wire.
A lamp in a lamp socket looks like such a simple bit of pinball engineering. But, I hope that you now realize how complex it really is and how to best get those EM incandescent lamps of yours shining brightly, once again.