Step One: Power off, Check the Lower Board Fuses & Bridges.
With the game off remove each of the fuses one at a time and test with a Multimeter (DMM) set to continuity. If a fuse is blown, just don't replace it (just yet). Fuses often blow for a reason. Note what the fuse does (there should be labels for each of the fuses).
If for example the fuse for the CPU driven 6 volt lamp power is blown, test its accompanying bridge rectifier (because if the bridge is shorted, its accompanying fuse will blow). There's only two bridge rectifiers in a system1 game (25 volts coil power, 6 volts cpu driven lamp power.)
If the 69 volt fuse for the score displays is blown, this often means one of the power supply's four 1N4004 diodes used for rectifying this voltage is shorted. If a 6.3 volt general illumination lighting fuse is blown, that can often mean a shorted light socket on the playfield.
Now that the lower fuse panel is all checked out, REMOVE the 25 volt solenoid fuse before proceeding! Set it aside for later.
Step Two: Power off, Check Playfield Coil Resistance.
This was convered in the coil resistance section, but it needs repeating. If a driver board transistor shorted or there is a ground issue, a coil can lock-on and burn. If this is the case, either cut the non-banded diode lead going to the coil, or replace the coil. I do this before initial power-up. Because a burned (shorted) low-resistance coil can damage the driver board.
Step Three: Isolate the Power Supply.
This simply involves removing the top J2 and right J3 power supply connectors. (The top connector supplies 5/-12 volts to the CPU and driver board, the right side connector supplies display voltages to the score displays.) Only the bottom J1 power supply connector is attached (makes sure it's attached properely too, because this connector can be reversed!) Now turn the game on. The power supply's top connector J2 can be checked for +5 and -12 volts DC. The right side connector J3 can be checked for 60, 42, 8 and 4 volts DC. (The power supply board is screened with the voltage outputs for these connectors.) If any voltages are missing, you will need to repair the power supply before continuing. (More information on that can be found in the Power Supply section.)
Step Four: Power Up with the CPU board Only.
Now that the power supply checks out, the CPU board can be added to the mix. All CPU connectors can be removed except for the left most J1 (power) connector. Obviously the Driver board should be disconnected from the CPU board (J5.) Also remove the two right side CPU connectors J2 and J3 (which go to the score displays.) Disconnect J6 and J7 (switch matrix) connectors too.