I HAVE A LOWRANCE LMS-334C IGPS THTEE SONAR AND THE GPS WORKS FINE I CANT GET THE MAIN MENU TO COME UP TO DELETE THE TRAILS THE MENU FOR THE SONAR AND GPS WILL COME UP JUST NOT THE MAIN MENU IT IS ONLY A YEAR AND HALF OLD

go to maps on your system follow the trail

Hello
I don't know whether you have made a factory reset to this device or not. If not, set it first and see whether it helps you. To make it factory settings:
[1] Press 'MENU""MENU" (down arrow to system setup) "ENT" (down arrow to RESET options/ ENT
[2] The unit asks if you want to reset all the options. Press [<---] to YES and then ENT. All options are reset, and the unit reverts back to map page at 4000 miles zoom range. Any recorded sonar logs of GPS data will be unchanged. OK.

http://primus.lowrance.com/support/resultDisplay.do;jsessionid=93352691ABEF9983BE5DDC0B1405D421?docType=1000&contextId=773:7.23,3621.3656,7.23&clusterName=ClusterPublic&docset=/Documents/Units/Lowrance/Combo&linktosource=1&responseId=135ccbe2cfd4f608:dcb03b:129e656421a:-62a8&groupId=4&answerGroup=1&score=985&page=http://primus.lowrance.com/icr/units/Lowrance/Combo/LMS527CDFiGPSPub.htm&result=0&excerpt=LMS-527C+DF+iGPS&resultType=5000#Goto7

I have the same problem on my 520C.
I have no solution but I hope you have find some?
Best regards
Dan

The LGC-2000 is bad would be the most likely cause, but if this started right after you changed the cables, Try connecting the NMEA 2000 network to a different power source than the main power. If you still have the original cables, and you didn't have the problem before, try using those again to make sure there isn't anything wrong with any of the new cables.

But most likely, the LGC-2000 is toast and you will want to contact Lowrance support to see about getting it repaired/replaced.

If it is normal in deeper water, it is most likely just returning stuff in the water (debris, algae, anything floating around...choppy water can cause this). Try installing the latest updates from http://www.lowrance.com/en/Downloads/Product-Software-Updates/

If it doesn't help, adjusting the sensitivity or setting the SURFACE CLARITY option from the SONAR FEATURES menu to LOW, MEDIUM, or HIGH...whichever gives the best results.

I hate to be the bearer of bad news, but it sounds like your internal module is on the fritz. I am pretty sure you can buy a external puck and a harness and it will work perfect. I did that with my hummingbird 997.

I think I can help with your issue. I have an LMS 334c and have had a few issues in the past. Called the factory (this answer is not listed any where in your manual) and they instructed me to "Soft Re Boot" my unit and it would put everything back to factory settings. Try this anytime it does not respond for whatever reason.

Turn the unit off.

At the same time press the Pages and Power button. Hold both down until you see the square box come up in the screen. You should have your factory settings again. May need to try a few times.
Lowrance said it works just like a computer, ever now and then it just tries to disect to much information at one time and hangs up.
Good luck. James Cantwell

Hi,

you can find the manual here,
www.lowrance.com/upload/Lowrance/Documents/Manuals/LMS339cDF_iGPS_0152-011_011206.pdf

Hope my info solves your problem,
Thanx for using fixya.....

I would verify that your "chart speed" is set to 100%.

Triton72