Table of Contents
Advertisement
DC Protection
Overview
The RA-4 chassis employs protection for over and under voltage, as well
as over current for the +135 volt line. The +22, +19 and +7 volt lines are
monitored for low voltage. IC6102 is used to sense over voltage and over
current for the +135 volt lines.
Shut Down
Shut down occurs whenever a condition in the protect circuits causes the
Q6103/B to go HIGH. A HIGH on Q6103/B turns it ON, causing it to turn
ON Q6102. This drops the drive voltage to Relay Drive Q6104/B, turning
it OFF. This removes the ground return path for IC6011 and the unit shuts
OFF. During shutdown, the voltage from the RM+5 volt line maintains the
latch.
+135 Volt Over Voltage
The +135 volt line is input to the protection circuit through D6101 and then
to a voltage divider consisting of R6101 and R6102. The voltage devel-
oped across R6101 is applied to IC6102/5 Non-inverting input. IC6102/6
Inverting input has a voltage applied to it from the voltage divider consist-
ing of R6110, R6103 and R6104. IC6103 is a programmable zener diode,
which is used to stabilize the reference voltage at IC6102/6. This voltage
is approximately 2.4 volts and will vary about .1 volts since the entire
circuit uses a floating ground. If the voltage at IC6102/5 rises above the
2.4-volt reference, then the output at IC6102/7 will go HIGH. This occurs
when the +135 volt line is at about +146 volts.
This High output is then applied to the latch circuit and to IC1009 on the A
board for the Self Diagnostic feature. If OVP occurs, the Timer LED will
flash three times. See the Protection Block section for more details.
27
+135 Volt Over Current Protection
The over current protection circuit works by monitoring the voltage divider
network that consists of R6110, R6103, R6104 and R6118. Essentially
we can look at this as the voltage across R6118 since the voltage at
IC6102/2 will change with it. This resistor is connected between T601/7
and ground. Since T601/7 is the center tap of the winding that supplies
the +135 volt line, any rise in current sourced by that line will cause the
voltage across R6118 to lower. This voltage is input into IC6102/2 Invert-
ing input. IC6102/3 Non-inverting input is connected to ground. There-
fore, if the current draw on the +135 volt line should cause the voltage at
IC6102/2 to become negative, a HIGH will be output at IC6102/1. This
HIGH output is applied to the latch circuit and also to IC1009 on the A
board for the Self Diagnostic feature. If OCP occurs the Timer LED will
flash twice. See the Self-Diagnostics section for more details.
+19, +22, +7 Volt LVP
This protection circuit works by looking at the difference in voltage be-
tween the +19, +22 and +7 volt lines and the +11 volt line. If the +19 or
+22 volt lines should drop .6 volts below the +11 volt line, this would cause
Q6101 to turn ON. If the +7 volt line should drop below 3.5 volts, this
would also cause Q6101 to conduct. When Q6101 conducts, it places
the +11 volt line on its collector. When this occurs, the latch circuit turns
ON and shuts the set down. When this circuit is activated, there is no
indication given by the Self Diagnostic circuit. See the Self Diagnostics
section for more details.
Advertisement
Table of Contents
Troubleshooting
