5-17
There are two LEDs of interest. ‘LED A’ flashes when 120 kHz is transmitting. ‘LED B’ flashes when
410 kHz is transmitting.
3. SIB Board.
There are four LEDs of interest. They have the following status when the system is operating
properly.
D1 Off D3 (Orange) Flashes at 2 Hz
D2 Off D4 (Green) On
SSB Board Test Points
1. GAIN A and B test points show the positive-going TVG ramp voltage for the low and high-
frequency sonar channels.
2. Four test points monitor the TVG’d analog sonar data. They are:
ADC 0 Port SSL ADC2 Stbd SSL
ADC 1 Port SSH ADC3 Stbd SSL
These test points are useful when doing a rub test.
DDC Test points
This board does not have any test points. The LEDs display the channels on the card that are running. Side
A and Side B. In a normally operating fish with both channels collecting data, the lights will alternate.
Modem Board Test Points
1. FSK.
Monitors the 3200 kHz to 2800 kHz frequency-shift-keyed signal from the topside unit. This signal
is used for optional commands. May not be present in all systems.
2. Trig.
A TTL signal that synchronizes the topside and sub-sea units with other topside equipment.
Follows the SYNC signal input on the topside unit. It is not used in all system configurations.
Other Checks
Periodically check the integrity of the sea ground capacitor attached to the rear bulkhead.
5.6 Tow Cable Troubleshooting
Historically, most system problems occur in the tow cable and their connectors. Before proceeding, verify
cable continuity from the shipboard end of the cable to the tow fish. The presence of a shorted or open
wire in a tow cable can be determined by using a multi-meter. An open or shorted wire can be located
using the techniques described in the following subsections.
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