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, 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 full CW, 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.
INTERNAL ADJUSTMENT LOCATIONS:
V REG: Regulator voltage
AGC: U2 AGC threshold
M ZERO: Panel meter zero
BFO: Carrier osc. freq.
VFO CAL: VFO freq. adj.
IF1,IF2: IF ampl. peak
L1,L2: RX front end peak
L5,L6: TX filter peak
CAR BAL,T3: Carrier null
PA BIAS: PA idle current
SP PROC: TX ALC level
MIC GAIN: TX audio level
TUNE SW: Full carrier out
PWR: Power on
VOL: AF Ampl. gain control
VFO TUNE: Sets operating freq.
FUSE: Reverse polarity protect
*If reverse polarity track fuse opens, install a miniature 2.5 A
pigtail fuse or a 3/4" hair pin loop of #32 wire.
PARTS PLACEMENT, MFJ 9420:
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
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