CHAPTER FIVE
MAINTENANCE/TROUBLESHOOTING
5.0 MAINTENANCE
This unit utilizes solid-state components. There are no moving parts (except switches etc.) or
parts with limited life.
5.1 ADJUSTMENTS
Periodically the internal time base may have to be nulled/calibrated due to aging and drift of the
oscillator.
5.1.1 INTERNAL OSCILLATOR CALIBRATION
It is recommended that the oscillator be nulled when the DAC value starts to approach 5,000 or
60,000.
The GPS TC&FG will have one of three oscillators installed in it:
• A voltage controlled temperature compensated crystal oscillator (TCXO) located on the GPS
Main Assembly 100015 in location Y3.
• A low noise oven oscillator located on the GPS Main Assembly 100015 in location Y1.
• An X72 or LPRO rubidium oscillator attached to the bottom plate of the chassis assembly.
This oscillator has no mechanical adjustment.
There are two methods to null/calibrate the internal oscillator. Use whichever method is suitable
to your means and capabilities.
A. First Method
The oscillator can be nulled against a known frequency standard with an
oscilloscope or other suitable means by using the following steps:
1. Turn on the unit and wait approximately one hour for the oscillator to warm up
and stabilize.
2. Sync one trace of an oscilloscope on the known frequency standard. Using the
other trace, monitor the 10MHz output of the unit. Remove the top cover of the
unit.
Symmetricom Inc ET6xxx ExacTime GPS TC & FG (Rev C) 5-1
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