MFJ-9420 Installation Manual
20-Meter SSB Travel Radio
C. Connect Microphone.
D. Turn on unit.
VOLTAGE CHECKS AND ADJUSTMENTS: (use voltmeter)
A. VOLTAGE REGULATOR: Set R64 for 10.0 V at TP1.
B. RECEIVER AGC: Set R6 for 4.3 Volts at TP2.
VFO CALIBRATION:
A. Tune the VFO dial to 14.250 MHz (mid band).
B. Connect counter probe to U7 pin 6
C. Adjust L3 for 4.255 MHz readout.
BFO FREQUENCY CHECK AND ALIGNMENT:
A. Tune across 14.250 MHz. test signal (use generator).
B. Identify 2 peaks in passband by watching S-Meter.
C. Carefully set the VFO dial to lower frequency response peak.
D. Adjust BFO trimcap (C61) until CW note is 600 Hz.
E. Recheck. First peak should be at 600 Hz, second peak around 2000 Hz. Pitch of CW tones
should go DOWN as you tune UP in frequency, indicating USB operation.
CARRIER NULL: (use a second receiver to monitor beat note)
A. Short mic pin 4 to ground to kill mic pickup.
B. Key mic and monitor signal slightly off frequency.
C. Alternately adjust R36 and T3 for minimum carrier.
RECEIVER SENSITIVITY CHECK:
A. Connect weak 14.250 MHz signal source to antenna jack.
B. Tune in signal source for maximum S-Meter reading.
C. Touch up L1, L2, T1, and T2 for max SIG Meter reading.
TRANSMITTER BANDPASS FILTER AND COMPRESSOR ALIGNMENT:
A. Connect QRP Wattmeter with dummy load to ANT Jack.
B. Turn R61 fully CW and then the Press Carrier Switch (SW2).
C. Carefully touch up L5 and L6 for peak output.
D. Turn R61 CCW until RF output power drops by 10%.
If radio fails to operate properly after following these procedures, call 800 647 8324 for help.
*If reverse polarity track fuse opens, install a miniature 2.5 A pigtail fuse or a 3/4" hair pin loop of #32 wire.
DC VOLTAGE CHART TROUBLESHOOTING GUIDE
For advanced troubleshooters, the following are typical DC voltages found in the MFJ-9420.
Voltages were checked with handheld probe type DVM to minimize effects of lead inductance
and to limit the potential for RF feedback.
Vcc = 13.8 (Supply Voltage)
TP1 = 10.0 (LM-317 Output)
TP2 = 4.3 (AGC Bias Voltage)
INTEGRATED CIRCUITS: (TX checks made with mic. keyed, no audio)
-----------------RX-----------------
------TX-----
PIN U1 U2 U3 U4 U5 U6 U7
