Main Vco Troubleshooting - Motorola MTM800 User Manual

9.1 - 18

Main VCO Troubleshooting

Check components between
U5701 pin 5 & 6 and TP5701
Failure:
VCO signal level at TP5702 < -5dBm
Start
Connect the radio's accessory connector to the Tetra Com interface.
Connect the radio's antenna connector to the high power RF output
on the IFR.
Connect the 50 ohms RF probe to the low power RF input on the IFR.
Setup IFR:
Select high power output and low power input.
No System,
TX Test,
TX Frequency 386.675MHz
Spectrum Analyser
Set Reference Level to 10dBm.
Run Tetra Com script for RX test.
Measure RF levels and frequencies with the 50ohms RF probe.
Measure DC levels with a multimeter.
Yes
0.6V DC at
U5701 pin 6
No
4.6V DC at
C5343
No
Yes
Replace
5V DC at U5331
U5331
pin 30
No
Check for 9.3V at
U5322 pin 3 &
6 and L5301 before
replacing U5321
?
Yes
?
3.3V DC at
U5701 pin 14 & 18
No
?
Check for 9.3V at
U5321 pin 1 & 3
before replacing
U5321
TROUBLESHOOTING CHARTS: 450-470MHz
Tetra Com Script for RX Test
TEST_ENTER
DELAY 18
Check for "Radio HW is READY"
MODE IDLE
FREQ RX 460.025
L1TIMER ON
AVE 10
MODE RSSI
GO
Use STOP to terminate RSSI reading
Yes
Replace
U5701
?