Check every coil's resistance before first power-up

Steps

• With the game off, set the meter to its lowest ohms range and measure across each coil's lugs; expect 2 ohms or more.
• If a coil reads under 2 ohms, unhook the thin ground-side wire (non-banded diode lug) and measure again.
• If it now reads normal, the driver chain is shorted: replace the under-playfield transistor if used, the driver board transistor and its pre-driver.
• If still low, cut one diode lead and measure; normal now means the diode was shorted, so fit a new 1N4004.
• If still low with the diode off, the coil is shorted; replace it and fit a 1N4004 across it.
• Reconnect the power wire (usually the doubled or thicker wire) to the banded-diode lug and the thin wire to the other lug.

Systems

• Gottlieb System 1

Related tips

• Check every coil's resistance before first power-up
• Testing the diode on a coil
• Testing coil diodes on the auxiliary power driver board
• Wire an A-16890 relay coil to run on EM AC power
• Testing a coil diode
• Flipper stuck up with power on (Playboy and later)
• Which way a coil diode goes
• Which way a coil diode goes

Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)