6
Receiver (100-149)
Problem Troubleshooting Steps
100 Low (or no) audio
output from receiver,
or general receiver
gain problem
If you hear normal audio output on some
bands but not all of them, check the band-
pass and low-pass filters and T-R switch
(120)
Make sure you have headphones or speaker
connected and do not have the AF GAIN set
at minimum
Check the key jack for a short to ground
Make sure RF GAIN is at maximum
The AGC threshold control (R1, Control
board) may be set incorrectly. It is normally
set so that the voltage at U2 pin 5 is 3.90
volts (no antenna, RF GAIN at max). You
can set R1 for a slightly higher voltage at U5
pin 5 to increase the no-signal I.F. gain. If R1
is adjusted, you'll need to re-adjust CAL S HI
and CAL S LO (S-meter).
If you have the 160 m/RXANT option board
installed, you may have menu entry
R A N T
turned ON but no receive antenna connected;
this may affect only one band since
R A N T
can be set individually for each band.
Peak the band-pass filters if you have not
already done so
Check for ground shorts in the LPF and BPF
by first resetting all of the relays (065)
Turn the AF GAIN to maximum
If you don’t hear any “hiss” at the receiver
output, troubleshoot the AF amplifier (110)
Check the 8V regulated supply voltage and
troubleshoot if necessary (053)
Measure the 8R line (+8V receive) at the
anode of D6 on the RF board. It should be 8V
+/- 0.5V. If not, look for a problem in the 8V
switching circuitry (control board).
Try using signal tracing (see procedure later
in this section)
110 AF amp not
working
Use the menu to set a sidetone level of 60
(
S T L 0 6 0 ). Hold S P O T . If you hear a
strong tone, the A.F. amplifier itself is
probably working; check the mute circuit
(CTRL-Q6 and Q7) and trace the volume
control lines back to the product detector
(RF-U11)
Remove the control board and inspect the
entire A.F. amplifier and mute circuit for
mis-installed components, shorts, and opens
114 AGC or S-meter
not working
If AGC appears to be working but the S-
meter isn’t, try re-calibrating the meter using
C A L S H I and C A L S L O . If the S-
meter is “stuck,” you may have an open,
short, or incorrect component in the area of
U2 on the control board.
Make sure the RF gain control is at
maximum
If the AGC and S-meter are both not
working, you may have a dead 5.068 MHz
oscillator crystal, X1 (control board). Listen
for the 2
nd
harmonic of X1 at about 10.136
MHz while touching a screwdriver blade to
pin 7 of U1 (NE602). If you can’t hear this
signal, try soldering a 22 k resistor from pin 7
to pin 3 on U1 (NE602).
120 Signal loss only
on some bands
If you have the 160 m/RXANT option
installed, make sure you have menu entry
rANT set to OFF, or if it is ON that you have
a receive antenna connected
Try peaking the band-pass filters on the
affected bands
Inspect all components in the T-R switch
area, and check all T-R switch voltages
Trace the signal from band-pass filters back
all the way to the antenna using an RF signal
generator
Make sure the VCO is oscillating on affected
bands by using the frequency counter
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