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COLOR CAMERA
EBI-6351
pendent upon the base current of Q2. The
base current of Q2 is derived from the out-
put voltage, forming a closed -loop circuit.
A decrease in the output voltage causes the
base current of Q2 to drop, which results
in a decrease in the collector current of
Q2 and the base voltage of Ql. The increased
base voltage on Q1 turns it on harder and
causes the output voltage to rise, returning
the voltage to its set value.
The operation of the positive section of
the power supply 20 -volt regulator, Q3 and
Q4, and related components, is identical with
the negative section described previously.
Intercom Amplifier Board, PL -7781675
Refer to the Component Diagram, Fig. 63,
and the Schematic Diagram, Fig. 64.
The intercom amplifier, is used to provide
two-way amplification for the intercom head -
General
sets. The unit consists of a microphone am-
plifier, Ql, and a receiver amplifier, Q2.
The microphone stage is a common emitter
amplifier having a gain of approximately 40.
The output of this stage is direct -coupled to
the green and black wires of the input/output
transformer, Ti,
The receiving stage is a common emitter
amplifier having a gain of approximately 15.
The input signal for this stage is direct -
coupled from the yellow and white wires of
Ti. The output of Q2 drives the headset
receiver button. Sidetone cancellation is ac-
complished by feeding a small amount of the
microphone output through the receiver input
winding of Ti. The phases of the voltage are
such that this voltage counteracts the voltage
induced into the receiver winding by poten-
tiometer R5.
The secondary of transformer T1 has an
impedance of 600 ohms and is normally con-
nected to the party line bus of the intercom
system.
MAINTENANCE
To obtain maximum life and operating
efficiency from the Color Camera, follow
a regular preventive maintenance schedule.
Periodically, inspect the Camera for any
evidence
of component overheating which
would discolor resistors and wiring insula-
tion, thereby causing breakage and erroneous
operation. If suitable test equipment is avail-
able, give transistors a leakage and beta
(gain) test. Replace any questionable com-
ponent.
When conducting a maintenance analysis or
troubleshooting this equipment, the input sig-
nal must be checked first because most of
the Camera boards receive their input sig-
nals from other boards within the Camera
and from external sources.
Keep the equipment as clean and dry as
possible. An air blower or brush with long,
soft bristles makes an excellent dust re-
mover. A high-pressure air hose is not
recommended since it can cause dust par-
ticles to scratch the optical surfaces.
Before installing any replacement parts,
check the circuit to determine the cause of
failure. When replacing components, select
the proper replacement from the Parts List.
All components are listed by symbol number
and have their General Electric drawing
number and description given.
Preamplifier Board, PL -7674511G1, G2
Refer to Figs. 15 through 17.
1. Check the
d -c
input voltages. They
should read
+600,
+100, +20 -20, and -6
volts d -c.
2. Check the Camera blanking input.
It
should read 60 volts ± 5.0 peak -to -peak.
3. Check the calibrated 15 -kHz sawtooth.
It should be adjustable from 0.4 to 1.0 volt
peak -to -peak.
4. Check the signal output. It should be
typically 0.20 volt peak -to -peak into 51 ohms
for luminance and 0.30 volt peak -to -peak
into 75 ohms for chrominance.
25
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