"Testing for Power at the Coil.
If a coil doesn't work, and the transistor is good, test for power at the coil. Do this with the game on and in attract mode, and the playfield lifted.
Put your DMM on DC voltage (100 volt range).
Put the black lead on the metal side rail (ground) of the game.
Put the red lead on either terminal of the coil. It should read about 43 volts. On flipper coils, any of the three terminals should also read about 43 volts.
If you are missing voltage at the coil, check for a broken wire/connector, or blown playfield fuse (see below). Remember the power wires are "daisy changed" together. So a break in the power wire in a previous coil will cause the coils further down the line to not work.
Testing a Coil.
You can also test a coil for proper operation. With the game on and in attract mode, and the playfield lifted, try this:
Connect one end of a alligator clip and wire to the metal side rail of the game.
Momentarily touch the other end of the alligator clip to the coil's terminal with the non-banded side of the diode connected to it.
The coil should fire.
Note if you accidentally touch the banded side of the diode to ground, you will probably blow a fuse.
If the coil doesn't fire, you have a damaged coil or no power at the coil. Look for a broken wire going to the coil's terminal. You can also test the resistance of a coil. A good coil should be in the 3 to 15 ohm range."