(Vhf/Uhf, Closed Architecture, No Receive Audio) - Motorola HT 1000 series Theory/Troubleshooting Manual

No Audio at
Audio R755?
No
Audio at
Ext. Spk.
Ext.
NO
Spk.
Selected Check
? P403
U706, Pin 24,
Audio
YES
Pin 4,
U706
?
NO
Audio at U706
Pin 4, Pin 2
5V at NO
U709,
Pin 1?
YES
5V at NO
Collector
Q702?
YES
Is
NO
U706
Pin 20
low?
YES
Audio
YES Check C769, C770,
present at
C771, C772, C733
U706
If OK, Replace
Pin 8
U706
?
NO
Audio
YES
present at
U701
Pin 21
?
NO
Audio
YES
present at
U701
Pin 16
?
NO
Trace audio signal path
from jumper flex P301 to
Pin 16 of U701 for break
in audio path.
44
TROUBLESHOOTING FLOW CHART #6A

(VHF/UHF, Closed Architecture, No Receive Audio)

NO NO
Audio at
C306?
YES YES
No
Audio at
Int. Spk.
Check Spk.
Flex, P701,
L705, L706
Audio at YES
Check Spk.
Pin 2?
Flex, P403,
L704, L706
NO
NO
YES
7.5V at
U709, Pin
8?
NO
Check U706,
6.8V at
C765, C763,
base of
& C764
Q702?
YES
Replace Q702
Press
NO
Mon. Button
Is U706
Pin 20
Low?
YES
If radio is in
PL mode, check
that PL code is
correct
Check
Check
C718
MCU U705
Rotate
VOL. POT.
Check Voltage at
NO
C792 is changing.
Activity on U701
Data, SEL and Ck
Pins?
YES
If no audio, replace U701.
If weak audio, check
data sent to U701 is
changing as VOL. POT
adjusted before replacing
U701
Check Rx (Go to Troubleshooting chart #2A)
Check Flex P301, R775, C710
Check Control
Top Flex, P403
RF Controller
Flex P301, VOl SW.
Replace
U709
NO
P701
Flex
OK?
YES
5V at
U701 Pin
27?
NO
Increase
signal level to
–47dBm.
Radio OK?
NO
when RF applied
Rectify
Fault
Won't Unsq. Radio
Go To Controller
Troubleshooting
Chart #8A
Go To Controller
Troubleshooting
Chart #8A
YES
Check Squelch
POT Setting
If Sq. Setting = 0
YES
and radio does
not unsq., change
U701
Check RX.
Noise at
NO Check U3, if RX
C712 drops
front end is
working.
?
YES
REV.
MAEPF-23275-O