GPS7 module troubleshooting
d. Check for prope
r antenna power setting.
e. Check the Antenna Power LED. If the LED is red or blinking green,
check for a problem with the antenna or the cabling system, such as an RF
splitter that blocks or short circuits the antenna power DC v
oltage.
7. Check the DC antenna output power voltage. (See page 10-18, DC antenna
output power voltage.)
8. Repeat steps 1 through 5 of this procedure for the reference unit. If the
reference unit passes, then exchange antenna feeds between the reference unit
and the GPS7 unit under test and retest the GPS7 unit under test.
9. If the GPS7 unit under test does n ot receive a GPS signal on a known, good,
antenna, then replace the GPS7 module.
Check diagnostic reported
values
There are several internally detected physical measurements which are reported
by the GPS7 module. Check the following (see the TG8000 User manual for
detailed procedures).
Temperature: Temperature is detected on the Trimble GPS receiver board.
This temperature is normally about 15 °C above ambient temperature. If the
temperature is very high or low, check that the fan is operating, the installation
clearances are correct, and that all cables in the GPS7 module are connected
properly. If there is still a problem, replace the GPS7 module.
Tune – Phase: The Phase value indicates the s econd by second differences
between the Pulse per Second (PPS) signal from the GPS receiver and the
Local 1 PPS signal from the Master Time of Day clock. At lock this signal
should be n ear hex 8000 0000.
Tune – DDS: The DDS value is the control word the processor has written to
the clock synthesizer. In internal mode, this is the calibration value needed to
compensate for the any small error in the the master oven frequency. When
locked to a reference such as video or GPS, the DDS value is the value needed
to track the reference signal frequency. The valid range of the DDS word is 0
to 4,194,303. If the DDS word is near either end of this range, then the system
is near the frequency limits to which it can lock.
Voltage Mon 1 (+5V, +8V), Voltage Mon 2 (-5V rel to +3.3V): The voltage
monitors measure the mainframe supplies, If the display indicates they are
out of range, then check them manually. (See page 10-14, Power supply
test.)Ifoneofthesesuppliesisbad,thenreplacetheMainboard.Ifmanual
measurem
ent shows that the supplies are correct, then the GPS7 module is not
measuring them correctly. Replace the G PS7 module.
PHASE DET RAMPS (Up: A, Up: B), PHASE DET RA MPS (Down: A,
Down: B): These four values show critical values
in the phase detector. The
values may vary from unit to unit, as a result of the auto-calibration that
adjusts them, but if all the power supplies are good and any of the ramp
diagnostics indicate “WARN” (for Warning), then replace the GPS7 module.
TG8000 Multiformat Test Signal Generator Service Manual 10–13
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