testing voltage regulator

There is a way to bench test a regulator. It requires a variable voltage power supply, voltmeter, and a 50 Ohm resistor. The resistor serves to limit current in the field connection for test purposes. I use 0 to 30V supply, with a 0 to 3A current limit, it has built-in voltmeter an ampmeter. The regulator is powered from the supply, connect the regulator case to the - of power supply, the (I) terminal of the regulator to the + of the power supply. Also connect one lead the resistor to the +, and the other lead to the (F) terminal. Connect the voltmeter + to the (F) terminal and the - to ground. Start the powersupply at 12V, the voltage, at the field should be less than 1.5 Volts, increase the power supply voltage to around 13.8V, the field terminal voltage will rise immediately, and follow the supply. Do not go higher than 15V.

The voltage point where the F goes high is the voltage where the regulator regulates. A voltage below, turns a transistor on, sinking the field to ground, the other field lead is high so the field is energized. The alternator increases voltage, the F terminal goes high, reducing field current. In normal operation, it toggles at a high frequency as needed to regulate.