Motorola MTP700 Detailed Service Manual page 113

TRANSCEIVER 400 MHz
Escort Troubleshooting (Cont.)
Supply problem?
ESC_VCO_BUF_EN
Perform VCO Test
1. Probe at R7514 using spectrum
2. Connect external supply (1.5V to 4.5V) to L7502
3. Adjust the external supply and check the
frequency range
380MHz to 430MHz
VCO is working properly. Check the
buffers and feedback path to FREQB.
Probe at C7031 and measure the RF power.
fall within 0 to -10dBm
Check Escort IC functionality in close
loop. If control voltage at L7502 is stuck
at HIGH (>4V), disconnecting C7031 will
make the control voltage stay at LOW
(~1.25V). If control voltage stays at LOW,
disconnecting C7003 will make the
control voltage stay at HIGH.
Escort
OK
MTP700 Portable Radio / Detailed Service Manual
A
Yes
No
Is
No
on (2.775V)?
Yes
Is frequency
No
covered?
Yes
No
Does the RF power
level?
Yes
Yes
Does Escort IC behave
correctly?
Perform
Controller Test
Check for shorting
on ESC_VCO_BUF
line and perform
Controller Test
Check TX VCO components for soldering
problem and compare with parts list value.
Check also the current drain of Q7501 and
Q7502 & Q7503, which is about 10mA at
R7512 and 2.6mA at R7511.
Escort
OK
No
Change Escort IC (U7001) and
perform the Escort Test again.
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