4.1 - 86
MTP700 Portable Radio / Detailed Service Manual
TRANSCEIVER 400 MHz
Synthesizer & VCO Troubleshooting
Use this test on a unit with the following symptom: no Tx or Rx.
Using a 50-ohm probe on the
spectrum analyzer, check the
LO output at the buffer output
at C3024 & C3025.
Is the frequency
at 514.65MHz?
Is the buffer
output between
-3 and 0dBm?
The unit tested successfully
Check the VCO output
at base Q3003, is the freq
514.65MHz?
Check for opens, shorts,
or missing components in
the buffer circuits.
Also check for 2.45Vdc on
E3001.
Test the VCO control
voltage at C3002. The
typical range is 0.2 to 4.9V.
Is the control
voltage railed to
<0.2V or >4.9V
Possible prescaler
feedback problem:
1. Check soldering of
C3022.
2. Probe to determine
if LO is reaching the
prescaler input.
A
YES
YES
YES
YES
NO
NO
NO
Note: This is
the abnormal
condition.
TetraCom Commands
> 11 timer on
> freq rx 405
> mode rssi
> main_vco on
> 11 timer off
NO
Содержание IMPRES Tetra MTP700
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