The plastic form used to make pinball coils can crack or break. The part
that usually breaks is the shelf which secures the lugs. Wire from the coil
is soldered to these lugs (sometimes accompanied by a diode), and wire from
the game is also soldered to these lugs. Through use, abuse, and misuse, the
shelf gets damaged. Actually, over time, the heat generated from the coil
itself dries out the plastic and makes it brittle. A cracked or broken shelf
can cause the coil and, therefore, its function (i.e., flipper, pop bumper,
kicker, etc.) to fail or become intermittent, or it may even cause a blown
fuse. This physical break relates directly to an electrical break (or OPEN)
in the circuit (NOT a SHORT). If the break is bad enough, the lugs may then
SHORT to nearby metal objects, such as mounting brackets.
I have seen broken coil forms in many electromechanical pinball machines. I
have even seen them in some newer, solid-state machines. Fortunately, this
problem is quite easy to fix. The best method I've found is to use a hot
glue gun at the point of break or fracture. NOTE: The broken shelf will
usually cause broken wires or solder joints, therefore, a soldering repair
must accompany the shelf repair.
When you make the shelf repair, be sure to use enough glue to ensure that
your repair will hold up under the constant heat and vibration of the
pinball machine. Place the glue directly above AND below the point of break
or fracture. Be careful not to use so much glue as to interfere with the
action of the part driven by the coil. The glue will cool and set within one
minute. Remember, for safety's sake, always perform your repairs with the
machine unplugged, and always double check your work.