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Maintenance, Calibration, and Troubleshooting
Overall Fail Circuitry Associated with the ECS Test
5
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5.11 Overall Fail Circuitry Associated with the ECS Test
Because the ECS Test involves circuits on the switch printed circuit board, power supply printed circuit
board and relay driver printed circuit board, as well as those on the ECS printed circuit board, a fairly
detailed study of this overall circuitry has been included. The study is devoted not only to circuitry, but in
great part to the interconnections between the printed circuit boards involved.
5.12 Starting With Pins M and P on the Power Supply
Schematic
These pins are ultimately connected to the two inputs of OP AMP U2.
The muting signal input, (15 V), is connected to pin 2 (-). It must pass through a diode to get to pin 2.
There is also a second input to pin 2 from the high voltage 506 V. But the second input is connected to
pin 2 by high resistance, and even if the high voltage falls to 0, the muting signal can overcome it, and
prevent the circuit from going into an alarm condition.
A voltage of either 0 V or 14 V is connected pin 3 (+) of the OP AMP. (There is also connected to pin 3 a
resistor of 130 kilohms whose other end is at 6.2 V.) In the operation of the OP AMP, a 0 V input to pin 3
is a pass condition (green light will stay on) and 14 V is a fail condition (green light will go off), and alarm
relays will be de-energized.
The output of the OP AMP goes from terminal N of the power supply board to the fail/safe circuit on the
relay driver board, via terminal H.
5.13 Starting With Terminal H on Relay Driver Board
If the input on pin H is low (-9.25 V measured), the output on pin 4 of the K503 solenoid is low (0.148 V
measured). When the input on pin H is high, the output is high (14.5 V measured). When pin 8 of U503 is
low, the solenoid has almost 14 V across it and is energized; when pin 8 is high (U503 cut off), the
solenoid has no voltage difference across it. The common point connecting the collector of Q501 and the
base of Q502 has a high (SAFE) of only 0.8 V and a low of 0.03 V, but this change is enough to cause
switching, since conduction in Q502 occurs when its base rises above 0.5 V.
The output of the FAIL/SAFE circuit, on pin F, is connected directly to one terminal of the green lamp on
the switch printed circuit board (effectively also the panel), and the other terminal of the green lamp is
connected directly to +14 V. Consequently, a low input to pin H on the relay driver board puts 14 V on
both terminals of the lamp and goes out.
5.14 Provision of Inputs to Terminals M and P on the Power
Supply Board
Operation of the green lamp is the same for manual and automatic reset functions. The closing of the
ECS switch causes a sharp negative pulse to be generated by the differentiating circuit R217-C205. The
differentiated pulse is passed to the anti-initiate circuit whose purpose is to prevent malfunction in case
the ECS button is inadvertently pressed twice. The circuit consists of two sections of U208 (pins 3, 4, 5, 6,
and 7). It has two outputs:
1. From pin 5 a pulse is sent to U206, another pulse generator that provides a more powerful pulse or
the initiation of the low voltage ramp, 0 to 6.2 V.