Elecraft K2 Owner's Manual - Manual (Page 158)

6
Receiver (100-149)
Problem Troubleshooting Steps
100 Low (or no) audio
output from receiver,
or general receiver
gain problem  If you hear 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 AF GAIN not at minimum
 Check for missing audio filter option
(KDSP2 or KAF2) or their bypass jumpers
 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. Typical
voltage at U2 pin 5 is 3.80 volts (no antenna,
RF GAIN at max). You can set R1 for a
slightly higher voltage at U2 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 RANT
turned ON but no receive antenna connected;
this may affect only one band since
RANT
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
( ST L 060 ). 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 CAL S LO . 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 O F F , or if it is ON that you
have a receive antenna connected
 If K60XV option connectors are installed
(J13 and J15 on RF board), but the module is
removed, install C6 and W6.
 Peak appropriate band-pass filters
 Inspect T-R switch components and voltages
 Trace signal from band-pass filters to the
antenna using an RF signal generator
 Make sure the VCO is oscillating on affected
bands by using the frequency counter