TRANSCEIVER 400 MHz
MTP700 Portable Radio / Detailed Service Manual
4.1 - 85
2nd LO Troubleshooting
Perform the following:
1. Remove the 2nd_LO shield.
2. Set the Unit to continuous
receive mode (Rxtdm).
3. Measure the 2nd_LO control
voltage between C1512 & R1512.
Check for feedback problem.
1. Check soldering of C1544,
L1541, C1543 and C1542.
2. Measure the RF power level
at Pin 5 of the LMX at 219.3MHz.
Check DC supply for the
VCO:
1. Check for 2.45V on
L1522, R1524 and C1527.
2. Check for
TETRA_2nd_LO_En on
Q1531.
Is the control voltage
between 0.5 and 4.5Vdc?
Measure the RF power at
C1544 at 219.3 MHz.
Is the power level
-10dBm
±
1dB and stable
on frequency?
The 2nd_LO VCO/Synthesizer
is O.K.
Check Q1521, R1524 for
soldering problems and
for the right values.
(compare with BOM)
Does the VCO have
its DC Supply?
Check DC supply for the LMX.
1. Check for 5V_RF on C1501, C1504.
2. Check 2.775V_WPIC on C1502.
Does the LMX have
its DC Supply?
Perform VCO_ONLY TEST
1. Connect at external 0.5 to 4.5V
power supply to R1512.
2. Measure the RF freq at C1544.
3. Adjust the external supply voltage
until the frequency is 219.3 MHz.
Can the frequency
be set to
219.3MHz?
The VCO is working properly.
The problem is with the LMX.
Replace the LMX.
Check DC
Block
Check DC
Block
Check all VCO components
around Q1521 for soldering
problems and compare
with BOM values.
Yes
Yes
No
No
No
No
No
Yes
Yes
Yes
Содержание IMPRES Tetra MTP700
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