78
OPERATION
Normal operation is indicated by a green light
in the lower left corner of the front panel. A red
light indicates that the input signal is too low to
maintain the set amplitude output.
TROUBLESHOOTING
WARNING: Dangerous voltages are present
on the printed circuit board. Always turn the
power off and disconnect the line cord before
removing the cover or changing components.
If front panel indicator is not lit, check the rear
panel power switch, the power cord, and the
fuse. If the Signal indicator is red, check for
proper input signal frequency (10 MHz ± 1%)
and sufficient amplitude. Also, check for opens
and shorts on the input and output connections.
CALIBRATION
Either J50 or J75 (not both) should be installed
to match the input signal impedance (50 or 75
ohms, respectively). The output level can be
set to any level from .75 to 1.25 volts peak to
peak by adjusting P1. Of the 8 round holes in
the top of the box, P1 is accessible through the
right-rear position.
CIRCUIT DESCRIPTION
T1, L101, C101, R101, and R102 comprise the
input network and provide ground isolation,
bandpass filtering, and impedance matching.
The signal is amplified by U1 and further
filtered by a "stagger tuned" network consisting
of L103, C107, R105, C108, C109, and L102.
U2 controls the gain of U1 by comparing the
peak voltage at L102 with the reference
voltage from P1, R117 and R118. D1 indicates
loss of signal (red) if the control voltage from
U2 becomes less than -2.5 volts. Q8 buffers
the signal for distribution to the output
transistors Q1 through Q7. Final bandpass
filtering and impedance matching is provided
by L11-L71, C11-C71, and R11-R71.
LINE VOLTAGE SELECTION
The FS710 operates from a 100, 120, 220 or
240 Volt AC nominal, 50 or 60 Hz power
source. Before applying power, verify that the
line selector card (located in the power entry
module) is in the correct position. The
selected voltage is indicated by the white dot
on the voltage list.
To change the line voltage selection,
disconnect the line cord and remove the fuse
module with a small screwdriver. Pull out the
voltage selection card (located at the right of
the power entry module) with a pair of needle
nose pliers. Rotate the plastic indicator until it
lines up with the correct voltage indicated on
the fuse holder and reinsert the card. Install the
correct fuse, reinsert the fuse holder and
replace the line cord.
LINE FUSE
Verify that the correct line fuse is installed
before connecting the line cord. The rear panel
indicates the correct fuse size, 1/4 Amp @
100/120 Volts or 1/8 Amp @ 220/240 Volts. If
necessary the fuse can be changed as
indicated in the line voltage selection section.
