Synthesizer Troubleshooting; Handling Boards Containing Cmos Ic Devices; Table 14 Synthesizer Troubleshooting Chart - Motorola Spectra Service Manual

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
(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.
Symptom
Does not lock on 1.
any channel
2.
3.
4.
Does not lock on 1.
some channels
2.
3.
Does not lock in Tx 1.
(or talkaround
or receive)
2.
Synthesizer locks 1.
on wrong
frequency
2.
3.
4.
5.
40
are of the CMOS
Table 14. Synthesizer Troubleshooting Chart
Possible Cause
VCO
Reference oscillator
Command board
RF board
Programming
(EEPROM)
VCO
RF board
RF board
VCO
Synthesizer not locked
Reference oscillator not
on frequency/working
Command board
Programming
(EEPROM)
RF board
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.
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.
Correction or Test (Measurements Taken at Room Temperature)
With radio in receive mode; unplug loop feedback coax from VCO board to RF board;
measured level should be –5dBm ±6dB; frequency should be 407 to 411 MHz; if not, replace
VCO board.
Is there > 1.5V p-p of 2.1 MHz on pin 21 of J500? If not, replace reference oscillator or
RF 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.
Replace RF board.
Check mode programming information to ensure that the correct frequency programming
information has been entered.
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.
Replace RF board.
Check the aux bit states (pin 9 & 11 of J601)
Receive: pin 11 > 8V; pin 9 > 8V
Transmit: pin 11 > 8V; pin 9 < 1V
Talkaround; pin 11 < 1V; pin 9 < 1V
If wrong, replace RF board.
Replace VCO board.
Check synthesizer lock line (pin 14 of J500); if > 1V, synthesizer is not locked; go to
Synthesizer not locked guide above.
a. Check reference oscillator frequency; should be 16.8 MHz ±4Hz;
THIS MUST BE MEASURED @ 25 deg. C (77 deg. F) ±3 deg. C TO BE ACCURATE.
b. Retune reference oscillator if frequency is incorrect.
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.
Check mode programming information to ensure that the correct frequency programming
information has been entered.
Replace RF board.
NOTE