(Vhf/Uhf Receiver Rf) - Motorola HT 1000 series Theory/Troubleshooting Manual

Inject RF
into J401
YES
IF Signal
at L20?
NO
YES
RF Signal
at T1?
1st LO
O/P OK?
NO Locked?
YES
RF Signal
YES
at L8?
NO
YES
RF Signal
at L6?
NO OR WEAK RF
YES
RF Signal
at CR109?
NO
Check harmonic filter L126-127,
ant. switch, CR109, J401 contact.
36
TROUBLESHOOTING FLOW CHART #2A

(VHF/UHF Receiver RF)

Bad SINAD
Bad 20Db Quieting
No Recovered Audio
NOTE: INJECT MODULATED
ON CARRIER FREQUENCY
SIGNAL AS REQUIRED
Spray or Inject 1st IF into
XTAL Filter
YES
Audio
Heard?
Trace IF signal
from L20 to Q4.
Check for bad
XTAL filter.
NO
Check FGU
Check Mixer,
U2, T1.
Check filter between
U1 and U2.
Before replacing U3,
check U3 voltages.
Trace IF signal
path. Check signal
Check U1 Stage.
voltage at TP40.
Program filter to
schematic test freqs.
and check varactor
voltages.
YES
YES Check
Audio at
Controller
C306?
NO
IF FREQS:
44.85 VHF
73.35 UHF
NO
Check 2nd LO
Cntrl Voltage
at R16
YES NO
VCO
Locked?
2.1/2.4
Mhz Check
at Pin 13
J301?
Q4
NO
Collector
OK?
IF signal
present?
Check
YES
for
2.0VDC
NO
Check U3
(IF IC) pin 2
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.
NO
YES
Check FGU,
Chart #4A
Check Q4
YES
bias Circuitry
for Faults.
Rotate Freq. Knob
NO
Activity
Check P301. If
On U3
OK, Check
Sel Pin?
Controller.
YES
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.
MAEPF-23269-O