Motorola MTP700 Detailed Service Manual page 197

TRANSCEIVER 800 MHz
Escort Troubleshooting (cont.)
Perform VCO Test
1. Probe at R459 using spectrum
2. Connect external supply (1.5V to 4.5V) to L461
3. Adjust the external supply and check the
frequency range.
806MHz to 870MHz
VCO is working properly. Check the
buffers and feedback path to FREQB.
Probe at C461 and measure the RF power.
Check Escort IC functionality in close
loop. If control voltage at C475 is stuck
at HIGH (> 4V), Disconnect C461 will
make the control voltage stuck at LOW
(~1.25V). If control voltage was stuck at
LOW, disconnect C460 will make the
control voltage stay at HIGH.
Escort
OK
MTP700 Portable Radio / Detailed Service Manual
A
Yes
Supply problem?
No
Does frequency
No
was covered?
Yes
No
Does RF power fall
within 0 to –10dBm
level?
Yes
Yes
Does Escort IC behave
correctly?
Perform
Controller Test
Check C476, C477, C478, C479, C480,
C481, C482, C487, D460, L462, L463,
L464, L465, L466, Q463, R470, R471,
R468 for soldering problem and compare
with BOM value.
Check also the current drain to Q463 and
Q464 which is about 8mA to R468 and
16mA to R483.
Does
ESC_VCO_BUF_EN is
on (2.775V)?
Yes
Check C490, C461, C489,
R470, R476, R477, R479,
R482 for connection
No
Change Escort IC (U460) and
perform the Escort Test again.
No Check for shorting
on ESC_VCO_BUF
line and perform
Controller Test.
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