(Vhf/Uhf Voltage Controlled Oscillator - Vco) - Motorola Handie-Talkie MTX Series Theory/Troubleshooting Manual

VCO TX/RX UNLOCK
Check
VDC at
C246
(VCTRL)
VDC
NO
Replace
13V/0.7V/
U201
Drifting
?
YES
For VHF
4.6V at
check L217.
NO
Collector
If OK
of Q202?
replace
U201.
YES
Power at
collector of
Q202?
YES
Voltage
YES
Check
at U204
U204
Pin 21?
NO
3.3V
Check L205 &
NO
between
R220. If no fault
C2118 &
found, replace
C212?
U201.
YES
Replace
U201
42
TROUBLESHOOTING FLOW CHART #5A

(VHF/UHF Voltage Controlled Oscillator - VCO)

RX
* NOTE: If C240 is found
ONLY
defective, change to 2.7PF (VHF)/
2.4PF (UHF1)/2.4PF (UHF2)
Replace components & go
to -VEE crossover freq.
tune procedures. Chart #9
except if L208, L209 are
changed.
TX
NO
0.1V at YES
U201
Pin 7?
RX
NO
YES
0.7V at
U201 Pin
5?
NO
Check
L221 &
U204
Replace
U201
TX
ONLY
YES
Is
L207 (UHF)
208/209/
210/219
open
NO
Is
*
C235-C241, YES YES
CR207 (UHF)
CR201
open
NO
Check
R203, R204,
R205, R209,
& Q202
* NOTE: If C240 is found
defective, change to 2.7PF (VHF)/
2.4PF (UHF1)/2.4PF (UHF2)
Replace components & go
to -VEE crossover freq.
tune procedures. Chart #9
except if L213, L215 are
changed.
YES
Is
0.1V at
YES
L215, L216,
U201
L211, L213,
Pin 14?
open
NO NO
Is
C219, C220,
4.4V at
C222, C223,
U201 Pin
C226, C227,
5?
C270, CR203
open
NO NO
Check
L221 &
Voltages
YES
U204
at U201 Pin
11 & 12
OK?
NO
Check
Replace
R23, R206,
U201
R217, R219
& R210
*
YES
MBEPF-23273-O