There are those who advocate simply replacing the bulbholder, or tumbling it. Any soldering beneath the playfield always involves the risks of collateral damage - melting some insulation somewhere, a rogue splat of solder forming to cause damage now or later, mixing up wires, mixing up diodes ......
Cleaning the inner surface of the holder is easy, the tried and tested small roll of plastic abrasive matting kept in a roll with some insulation tape, like this ...
The hard bit is cleaning the spring at the bottom. But i have cracked it. I had a dead bayonet holder on my funhouse that was not visibly corroded, it was actually quite shiny. The problem was a dirty spring contact in the middle
You use a "brad point wood bit" and hand turn it. These have a point that locates it in the centre of the spring. The cutting surface is curved so it naturally cuts a nice new surface on the curved wire of the spring. They are also extremely sharp so with about 4 hand turns you can actually see the new shiny contact
Different makes of drill bit will have different cutting profiles, but a 3mm to 5 mm one should do the trick
Cleaning the inner surface of the holder is easy, the tried and tested small roll of plastic abrasive matting kept in a roll with some insulation tape, like this ...
The hard bit is cleaning the spring at the bottom. But i have cracked it. I had a dead bayonet holder on my funhouse that was not visibly corroded, it was actually quite shiny. The problem was a dirty spring contact in the middle
You use a "brad point wood bit" and hand turn it. These have a point that locates it in the centre of the spring. The cutting surface is curved so it naturally cuts a nice new surface on the curved wire of the spring. They are also extremely sharp so with about 4 hand turns you can actually see the new shiny contact
Different makes of drill bit will have different cutting profiles, but a 3mm to 5 mm one should do the trick