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HARDWARE TROUBLESHOOTING PROCEDURES
The following procedures describe a few simple tests as an aid in
debugging hardware problems. First, make sure that the FS700 is not
locking or searching by entering the TRACKING menu, setting the
SEARCH MODE to MANUAL, and stopping the lock. The FS700 has
two calibration menus (CAL MENU 1 and 2) that are accessed by
pressing the BSP key simultaneously with either the TIME or FREQ
key. It is helpful to read the circuit description for the relevant section
before attempting troubleshooting.
16 Bit DAC Test
The FS700's 16 bit DAC may be directly set from the front panel for
test purposes. Enter CAL MENU 2 by pressing the BSP and FREQ
keys together. The field displayed allows the 16 bit DAC to be set to
any value between -32767 and +32767. This should produce an output
at the DAC between -3 V and +3 V. Each bit change produces an 92
mV step. The DAC should be accurate to ±30 mV ±2 % of setting.
RF Circuitry Tests
To test the RF circuitry, a 100 kHz signal must be applied to the
antenna input of the FS700. Because the FS700 is designed to provide
power to the active antenna, the 100 kHz signal must be applied through
a special ANTENNA TERMINATOR circuit shown in Figure 1. This
terminator allows application of a signal while maintaining correct DC
bias conditions.
Figure 1.
Antenna Termination Adapter
The FS700's rf attenuators may be set directly in CAL MENU 1. The
allowable range is 0 to 111 dB. With an input signal of 10 mV peak-to-
peak and the attenuators set to 64 dB, the FS700 should produce an
output of about 0.5 V rms at the LORAN OUTPUT BNC.
By adjusting the attenuators, the signal level, and measuring the output
level, the attenuator values may be checked. Be careful not to saturate
any of the gain stages.
