TM 1 1 - 5 8 2 0 - 9 2 1 - 4 0 - 1
Starting from condition A, the sequence of events for starting the +1600 Vdc High Voltage Power
d.
Supply, (assuming there is no fault) areas follows:
(1) Switching on the +26.5 Vdc power starts the time delay circuit cycle through its preset 60-
second delay period and applies operating voltages (except the +1600 Vdc) to all circuits in
the power amplifier.
(2) After 60 seconds, the timing circuit applies a high to pin 6 of NAND gate 1A2U1, enabling
the gate in preparation for the initiation of the Automatic Tune Cycle.
(3) When the power amplifier is keyed, the T/R LINE signal input to NAND gate 1A2U1, pins
8 and 9, is grounded. This produces a high at pin 5 of NAND gate 1A2U1 which, when
NANDed with the high from the time delay circuit, produces a low output which is inverted
and applied to the base of transistor 1A2Q8, turning it ON. This applies the HV ON signal
(ground) to HV ON relay 1A13A1K1, energizing it.
(4) The 1A14A3Q1 base-to-collector feedback path is completed through contacts B1 and B2 of
relay 1A13A1K1.
(5) When capacitor 1A13A1C1 discharges through 1A13A1K1, contacts A1 and A2, and resistor
1A13A1R10, transistor 1A13A1Q1 momentarily turns ON, providing a HV START pulse
(+26.5 Vdc) to the base of transistor 1A14A3Q1 through transistor 1A13A1Q1, resistor
1A13A1R12, and diode 1A13A1CR2.
(6) The dc-to-dc converter transistors (1A14A3Q1 and Q2) go into self-sustained oscillation at
2 kHz.
(7) The +1600 Vdc appears across bleeder resistors 1A13A1R1 through R7, developing the
+1600V SENSE signal which turns HV ON indicator lamp 1A13A1DS1 (Amber).
Note
After completion of steps d.(1) through d.(7), the active elements of the control
circuit are in condition B (see table 2-5). An overload condition is sensed by
the magnitude of the voltage drop across the 10 ohm resistors (1A13A1R8 and
1A13A1R9) between the negative (cathode) side of rectifier bridge 1A13CR2
and ground. This voltage (Ip SENSE) is applied to amplifier and latch 1A2AR1,
pin 3, in the DC Control PWB Assembly 1A2. Resistor 1A2R20 is adjusted to
approximately 3.5V as a reference so that when the current drain from the
+1600V power supply exceeds 700 mA, amplifier 1A2AR1 turns ON and latches.
The sequence of events after an overload condition has been sensed is:
(8) Transistor 1A2Q7 is turned ON by amplifier 1A2AR1, shorting the base of transistor 1A2Q8
to ground.
(9) Transistor 1A2Q8 turns OFF, de-energizing HV ON Relay 1Al3A1K1.
(10) When relay 1A13A1K1 de-energizes, it opens the base-to-collector feedback path of transistor
1A14A3Q1 and stops operation of the dc-to-dc converter.
(11) The +1600V across bleeder resistors 1A13A1R1 through R7 drains off, turning OFF the
1A13A1DS1 HV ON indicator light.
(12) When transistor 1A2Q7 is turned ON, it also grounds the PA FAULT line which is sensed by
the transmit-receive switching inhibit circuit in System Control PWB Assembly 1A3 and
transmit operation is inhibited.
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