TM 55-1930-209-14&P-12
1.1.3
Continued
The oscillator (inverter) is shown schematically on drawing M-2194-C. The nominal 12 V DC input is
connected to + (1) and -(4), and the driver leads to "D" (6) and "D" (7). Note driver leads receive AC, no
polarity (unless signals are stacked and phasing must be retained).
The inverter circuit terminal 2 is connected to terminal 1 on the timer board and is the positive supply for
the timer board. Terminal 3 is connected to terminal 2 on timer board and is the negative supply for this
board. Terminal 5 is connected to terminal 4 on the timer board and is the coding terminal for the
oscillator. (see drawing S-4368-C)
The regulator is turned on when it sees a negative on terminal 5. The oscillator may be keyed on
continuously for testing by connecting a 1000 ohm resistor from terminal 5 to negative A schematic of the
FA 390A Oscillator is shown in Drawing M-2194-C.
Assume that when the regulator is turned on Q7 conducts first. The following sequence of events will
occur, Current will flow through the upper half of the winding of T2. By transformer action, Q8 will be cut
off (open switch) due to lowered net voltage on the collector, and reverse bias being developed on the
base. Shortly after current has started to flow Q7 will be driven into saturation (closed switch) placing most
of the battery voltage across the upper winding of T2. The current through this winding will now be
Form No. 6310 0238
