MAINTENANCE/TROUBLESHOOTING
2. Read the DAC value either from the RS-232 I/O port, or from the LCD
display.
3. Remove the top cover. Locate the oscillator and its adjustment access hole.
4. SLOWLY (no more than 45
o
each time) adjust the oscillator and watch the
DAC value change. If the DAC value is 65535, turn the oscillator adjustment
counterclockwise, which will decrease the frequency and the DAC value. If the
DAC value is 00000, turn the oscillator adjustment clockwise, which will increase
the frequency and the DAC value.
5. Wait approximately one minute between each adjustment to allow the
oscillator to stabilize.
6. Keep adjusting the oscillator in the appropriate direction until the DAC value
is approximately at its midpoint (32767). Replace the top cover.
7. If after approximately one hour, the DAC value has changed by more than
±5,000 from 32767, repeat steps one through six.
5.1.2 LCD ADJUSTMENT
The contrast of the LCD display may be adjusted using potentiometer R99.
5.1.3 AC CODE ADJUSTMENTS
The modulation ratio of the AC code output can be adjusted from a typical range of 2:1 to 6:1. It
has been factory adjusted for a ratio of 3:1. The modulation ratio adjustment is potentiometer
R107.
The code output amplitude (level) is adjusted using potentiometer R108. It can be adjusted to
approximately eight volts peak-to-peak, terminated into 50Ω.
5.1.4 10MHz SINE WAVE
The amplitude (level) of the 10MHz sine wave output can be adjusted using potentiometer R30.
The nominal amplitude is approximately 1 volt RMS terminated into 50Ω.
5.1.5 10MHZ SQUARE WAVE
The duty cycle (symmetry) of the 10MHz square wave output can be adjusted to approximate
50/50% using potentiometer R60. When making this adjustment, monitor the 10MHz square
wave at the rear panel BNC output.
Symmetricom Inc ET6xxx ExacTime GPS TC & FG (Rev C) 5-3
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