36
TROUBLESHOOTING FLOW CHART #2A
(VHF/UHF Receiver RF)
Bad SINAD
Bad 20Db Quieting
No Recovered Audio
Audio at
C306?
Check
Controller
Spray or Inject 1st IF into
XTAL Filter
Audio
Heard?
Check 2nd LO
Cntrl Voltage
at R16
Inject RF
into J401
IF Signal
at L20?
RF Signal
at T1?
RF Signal
at L8?
RF Signal
at L6?
RF Signal
at CR109?
Check harmonic filter L126-127,
ant. switch, CR109, J401 contact.
Program filter to
schematic test freqs.
and check varactor
voltages.
If voltages OK check
varactor filter. If voltages not
OK, check U102. Check
also Q108, R115, U102
voltages. Check U102 can
be selected by MCU
before replacing U102.
Before replacing U3 check 2nd
VCO Q1. Check VCO O/P level;
C58, C95. Disconnect R117 and
verify that a 0.5V to 5V ctrl voltage
VCO will sweep about the IF freq.
Trace IF signal
from L20 to Q4.
Check for bad
XTAL filter.
VCO
Locked?
1st LO
O/P OK?
Locked?
Check FGU
Check Mixer,
U2, T1.
Check filter between
U1 and U2.
Check U1 Stage.
Before replacing U3,
check U3 voltages.
Trace IF signal
path. Check signal
voltage at TP40.
Q4
Collector
OK?
IF signal
present?
2.1/2.4
Mhz Check
at Pin 13
J301?
Check FGU,
Chart #4A
Rotate Freq. Knob
Activity
On U3
Sel Pin?
Check P301. If
OK, Check
Controller.
YES
YES
NO
YES NO
NOYES
YES
YES
NO
NO
YES
NO
YES
NO
NO
YES
YES
YES
NO
NO OR WEAK RF
YES
YES
NO
NO
NOTE: INJECT MODULATED
ON CARRIER FREQUENCY
SIGNAL AS REQUIRED
MAEPF-23269-O
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