Elecraft K2 Owner's Manual - Manual (Page 164)

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6. No-Signal AGC, Min. IF Gain: Measure the DC voltage on pin 1 of U2.
Expected: 4.6 V. Actual: _____.
7. Turn the signal generator back on.
8. AGC @ Saturation: Measure the DC voltage on pin 1 of U2. Expected:
6.9 V. Actual: _____. Adjust the VFO to make sure this voltage is at its
peak.
9. I.F. Amp AGC Input: Measure the DC voltage on pin 5 of U12 (RF,
sheet 2). Expected: 5.0 V. Actual: _____.
Product Detector and AF Amp (RF, Sheet 2)
1. Set up the DMM to read AC volts (use a 2 or 3-V meter range).
2. Touch the (+) lead of the DMM to pin 5 of U11 (NE602). Decrease the
signal generator level until the AC voltage at pin 5 reads .025 Vrms. (The
K2’s RF GAIN control should still be at minimum.)
3. Disconnect the headphones and speaker. Turn the AF GAIN control to
maximum.
4. Measure the signal at the speaker jack, P5 pin 1 (near the on/off switch,
S1). Expected: 1.6 Vrms. Actual: _____.
I.F. Amp Noise Gain (RF, sheet 2)
1. Turn the signal generator off and disconnect it from the antenna jack.
Connect a 50-ohm dummy load.
2. Turn off all nearby equipment (especially computers or signal sources).
3. Set AF GAIN to maximum. Set RF GAIN to minimum.
4. Make sure the preamp and attenuator are both OFF.
5. Verify that FL1 is selected (bandwidth = 1.50), as well as CW Normal
mode.
6. AF Output, Min. IF gain: Setup the DMM for its lowest AC volts
range. Measure the signal at the speaker jack, P5 (near the on/off switch,
S1). Expected: 0.000-0.001 Vrms. Actual: _____.
7. AF Output, Max. IF gain: Set RF GAIN to maximum. Measure the
signal at P5, pin 1. Expected: 0.007-0.013 Vrms. Actual: _____.
8. Preamp Noise Gain: Turn on the preamp. Measure the signal at P5.
Expected: 0.030-0.060 Vrms. Actual: _____.
9. Noise Increase w/Antenna: Connect an antenna. The signal at P5 should
increase substantially even if atmospheric conditions are quiet. A typical
reading on 30 or 40 m is 0.20-0.40 Vrms. In general, the longer or higher
your antenna is, the greater the noise increase will be.
Final Steps
If you have completed receiver signal tracing and any necessary repairs, you
should then do the following:
1. Re-install the bottom cover and heat sink.
2. Re-do calibration of the VCO, BFO, band-pass filters, crystal filters, etc.
as needed (see RF Board Alignment and Test, parts I, II, and III). If you
peaked L8 and L9 when signal tracing through the 30-m band-pass filter,
you’ll need to re-peak C21 and C23 on 20 m.
3. Leave the frequency counter cable connected to TP2 (BFO)
4. Connect the speaker and re-install the top cover.
Transmitter
The following procedure can be used to isolate problems with the transmitter
(the transmitter area of the RF board is identified in Figure 3). CW mode is
used for these tests. If you’re having difficulty with the SSB adapter, make
sure the transmitter works on CW first, then proceed with the signal tracing
instructions in the SSB adapter manual.
Once you find a location where the signal appears to be much lower than
expected, stop signal tracing and check that circuit. Check all component
values and DC voltages (see DC Voltage Tables). Closely examine the PC
board for unsoldered pins and solder bridges. One of most likely causes of a
transmitter problem is a poorly-soldered toroid lead. Re-heat any suspect
leads or solder joints.
Preparation for Transmitter Signal Tracing
1. Make sure basic display and control circuits are functioning before
attempting transmitter testing.
2. Remove the SSB adapter (if installed) and install temporary jumpers at
J9 and J10. Temporarily re-install C167 (.001 µF or higher) between pins
7 and 12 of J11. (See RF board, sheet 2.)
3. 12 V supply check: Use your DMM to check the DC voltage at the
cathode (banded end) of D10 (right edge of the board). Expected: 9 to 14
V. Actual: _____. Verify that the same voltage (or slightly lower) can be
found on the case (collector) of Q5 and the tab (collector) of Q6 when the
K2 is turned on and is in receive mode.