ELECRAFT K 2 Owner's Manual page 125

K2 Manual 1/24/99 V.XC ©1999 Elecraft
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 (counter-clockwise)
§
Check the key or key jack for a short to
ground
§
Make sure the RF gain control is not set for
minimum gain
§
If you have the 160m/RXANT option board
installed, you may have menu entry rANT
turned ON but no receive antenna connected
§
Peak the band-pass filters if you have not
already done so
§
Turn the AF gain to maximum (clockwise).
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).
§
Use a 3' long piece of hookup wire to do
"signal injection," working backwards from
the audio amplifier stage. Start by touching
the wire to pin 4 of RF/U11 (product
detector). If you don't hear a hum when you
touch the wire to this pin, the AF amp input
may be shorted or open on the control board.
Next, touch the wire to pin 1 on RF/U11. If
you don't hear an increase in noise, look for
a problem in the product detector circuit.
Continue tracing backwards until you find
where the signal is getting lost.
§
Try using signal injection if the problem is
occurring in an earlier stage of the receiver.
§
110 AF amp not Use the menu to set a sidetone level of 60
working (ST L 060). Press SPOT. 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
§
If you have the 160m/RXANT option
120 Signal loss only
on some bands 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
§
140 Receiver current If you saw the message INFO 140, your
drain is too high receive-mode current drain was measured at
over 400mA during normal operation.
Continue with the checks below.
§
Use DISPLAY to show voltage and current
on the LCD. If the current shown is >
300mA with no incoming signal or >
200mA with the bargraph turned OFF and
no signal, you may have a short or excessive
load on the 8V or 8R lines (053).
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