hello sorry to hear your issue .. I do have some suggestions for you to try.
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There are many factors which can influence your Sonar to not function properly.
It could be your sonar sensitivity settings, or your sonar calibration. Because there is so much depth relating to the sonar category I have taken the time to pull up your manual.
LCX-15mt Gps receiver review pages 12-24 on: sonar setup, calibration sensitivity, and other features.
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also in the back of the manual you will find sonar troubleshooting. I have also pasted it here for easy access.
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Unit freezes, locks up, or
operates erratically:1. Electrical noise from the boat’s motor, trolling motor, or an accessory
may be interfering with the sonar unit. Rerouting the power and transducer cables away from other electrical wiring on the boat may help. Route the sonar unit’s power cable directly to the battery instead of through a fuse block or ignition switch
2. Inspect the transducer cable for breaks, cuts, or pinched wires.
3. Check both the transducer and power connectors. Make certain both
are securely plugged in to the unit.
Weak bottom echo, digital readings erratic, or no fish signals:1. Make certain transducer is pointing straight down. Clean the face of thetransducer. Oil, dirt, and fuel can cause a film to form on the transducer,reducing its effectiveness. If the transducer is mounted inside
the hull, be sure it is shooting through only one layer of fiberglass and
that it is securely bonded to the hull. Do NOT use RTV silicone rubber
adhesive or Marinetex
2. Electrical noise from the boat’s motor can interfere with the sonar. Thiscauses the sonar to automatically increase its Discrimination or noise rejection feature. This can cause the unit to eliminate weaker signals such as fish or even structure from the display.
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3. The water may be deeper than the sonar’s ability to find the bottom. If
the sonar can’t find the bottom signal while it’s in the automatic mode,
the digital will flash continuously. It may change the range to limits far
greater than the water you are in. If this happens, place the unit in the
manual mode, then change the range to a realistic one, (for example,
0-100 feet) and increase the sensitivity. As you move into shallower
water, a bottom signal should appear.
4. Check the battery voltage. If the voltage drops, the unit’s transmitter
power also drops, reducing its ability to find the bottom or targets.
Bottom echo disappears at high speeds or erratic digital reading or
weak bottom echo while boat is moving1. The transducer may be in turbulent water. It must be mounted in a
smooth flow of water in order for the sonar to work at all boat speeds.
Air bubbles in the water disrupt the sonar signals, interfering with its
ability to find the bottom or other targets. The technical term for this is
Cavitation.
2. Electrical noise from the boat’s motor can interfere with the sonar. This causes the sonar to automatically increase its Discrimination or noise rejection feature. This can cause the unit to eliminate weaker signals such as fish or even structure from the display. Try using resistor spark plugs or routing the sonar unit’s power and transducer cables away from other electrical wiring on the boat.
No fish arches when the Fish ID feature is off:1. Make certain transducer is pointing straight down. This is the most
common problem if a partial arch is displayed.
2. The sensitivity may not be high enough. In order for the unit to display a fish arch, it has to be able to receive the fish’s echo from the time it
enters the cone until it leaves. If the sensitivity is not high enough, the
unit shows the fish only when it is in the center of the cone.
3. Use the Zoom feature. It is much easier to display fish arches when
zoomed in on a small range of water than a large one. For example,
you will have much better luck seeing fish arches with a 30 to 60 foot
range than a 0 to 60 foot range. This enlarges the targets, allowing the
display to show much more detail.
4. The boat must be moving at a slow trolling speed to see fish arches. If
the boat is motionless, fish stay in the cone, showing on the screen as
straight horizontal lines.
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NOISE
A major cause of sonar problems is electrical noise. This usually appears on the sonar’s display as random patterns of dots or lines. In severe cases,it can completely cover the screen with black dots, or cause the unit operate erratically, or not at all.
To eliminate or minimize the effects of electrical noise, first try to determine the cause. With the boat at rest in the water, the first thing you should do is turn all electrical equipment on the boat off. Make certain the engine is off, also. Turn the sonar unit on, then turn off ASP (Advanced Signal Processing). There should be a steady bottom signal on the display. Now turn on each piece of electrical equipment on the boat and view the effect on the sonar’s display. For example, turn on the bilge pump and view the sonar display for noise. If no noise is present, turn the pump off, then turn on the VHF radio and transmit. Keep doing this until all electrical equipment has been turned on, their effect on the sonar display noted, then turned off.
If you find noise interference from an electrical instrument, trolling motor,
pump, or radio, try to isolate the problem. You can usually reroute the
sonar unit’s power cable and transducer cable away from the wiring that
is causing the interference. VHF radio antenna cables radiate noise when transmitting, so be certain to keep the sonar’s wires away from it. You may need to route the sonar unit’s power cable directly to the battery to isolate it from other wiring on the boat.
If no noise displays on the sonar unit from electrical equipment, then make certain everything except the sonar unit is turned off, then start the engine. Increase the RPM with the gearshift in neutral. If noise appears on the display, the problem could be one of three things; spark plugs, alternator, or tachometer wiring. Try using resistor spark plugs, alternator filters,
or routing the sonar unit’s power cable away from engine wiring.
Again, routing the power cable directly to the battery helps eliminate noise problems. Make certain to use the in-line fuse supplied with the unit when wiring the power cable to the battery.
When no noise appears on the sonar unit after all of the above tests, then the noise source is probably cavitation. Many novices or persons with limited experience make hasty sonar installations which function perfectly in shallow water, or when the boat is at rest. In nearly all cases, the cause
of the malfunction will be the location and/or angle of the transducer. The
face of the transducer must be placed in a location that has a smooth flowof water at all boat speeds. Read the transducer instructions for the best mounting position.
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Glad to help..................... Good Luck
