40
V. SYNTHESIZER TROUBLESHOOTING
Table 14 lists a number of synthesizer-related
symptoms which may occur that interrupt normal radio
operation. Use this chart to help troubleshoot and repair
synthesizer problems to the board level. This chart
does not attempt to isolate problems to the component
level.
VI. HANDLING BOARDS CONTAINING
CMOS IC DEVICES
Many of the integrated-circuit devices used in com-
munications equipment are of the CMOS
(complementary metal oxide semiconductor) type.
Because of their high open-circuit impedance, CMOS
ICs are vulnerable to damage from static charges.
Everyone involved in handling, shipping, and servicing
them must be extremely careful not to expose them to
such damage.
CMOS ICs do have internal protection, but it is
effective only against over-voltages in the hundreds of
volts, such as those that could occur during normal
operations. Over-voltages from static discharge can be
in the thousands of volts.
To avoid damaging CMOS ICs, take the following
precautions when handling, shipping, and servicing
them.
1.
Before touching a circuit module, particularly after
having moved around in the service area, touch
both hands to a bare metal earth-grounded surface.
This discharges any static charge you may have
accumulated.
NOTE
Wear a conductive wrist strap (Motorola part no.
RSX-4015A) to minimize the buildup of static
charges on your person while you are servicing
CMOS equipment.
Symptom
Possible Cause
Correction or Test (Measurements Taken at Room Temperature)
Does not lock on
1.
VCO
With radio in receive mode; unplug loop feedback coax from VCO board to RF board;
any channel
measured level should be –5dBm ±6dB; frequency should be 407 to 411 MHz; if not, replace
VCO board.
2.
Reference oscillator
Is there > 1.5V p-p of 2.1 MHz on pin 21 of J500? If not, replace reference oscillator or
RF board.
3.
Command board
Do both the chip select lines (pins 16 & 20 of J500) go low during mode changes; is there data
on the clock & data lines going into the RF board (pins 18 & 19 of J500)? If not, replace
command board.
4.
RF board
Replace RF board.
Does not lock on
1.
Programming
Check mode programming information to ensure that the correct frequency programming
some channels
(EEPROM)
information has been entered.
2.
VCO
With radio in receive mode unplug loop feedback coax from VCO board to RF board; measured
level should be –5dBm ±5dB; frequency should be 407 to 411 MHz; if not, replace VCO board.
3.
RF board
Replace RF board.
Does not lock in Tx
1.
RF board
Check the aux bit states (pin 9 & 11 of J601)
(or talkaround
Receive: pin 11 > 8V; pin 9 > 8V
or receive)
Transmit: pin 11 > 8V; pin 9 < 1V
Talkaround; pin 11 < 1V; pin 9 < 1V
If wrong, replace RF board.
2.
VCO
Replace VCO board.
Synthesizer locks
1.
Synthesizer not locked
Check synthesizer lock line (pin 14 of J500); if > 1V, synthesizer is not locked; go to
on wrong
Synthesizer not locked guide above.
frequency
2.
Reference oscillator not
a.
Check reference oscillator frequency; should be 16.8 MHz ±4Hz;
on frequency/working
THIS MUST BE MEASURED @ 25 deg. C (77 deg. F) ±3 deg. C TO BE ACCURATE.
b.
Retune reference oscillator if frequency is incorrect.
3.
Command board
If reference oscillator won’t tune on frequency, is reference control voltage (pin 2 of J500)
tuning over 1.5 to 4.3 volts and is the 5 volt supply 5V ±.2V? If not, replace command board,
otherwise replace reference oscillator.
4.
Programming
Check mode programming information to ensure that the correct frequency programming
(EEPROM)
information has been entered.
5.
RF board
Replace RF board.
Table 14. Synthesizer Troubleshooting Chart
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