I think the only thing the manual mode does is stop the sensitivity setting from adjusting automatically. Running your unit in manual mode and turning down the sensitivity a bit will sometimes help in the weeds.

Try setting the ping rate at 50%, that seems to be the best for my unit for working in weeds.

Manual mode won't affect anything other than your sensitivity setting --- your color line settings and noise and surface clarity settings etc. will stay where they were unless you change them.

Good luck, hopefully the new software will cure the problem for you.

I have the same issue and have tried adjusting everything to no avail. My Eagle Fishmark 480 in the front of the boat has no problem but the 520 will not pick up bottom at all. I'll have to try the new software to see what happens.

I have a 520c as well. I have tried everything including the software upgrade. Still the same issue. I don't know what to do next?

I'm going to get a new Garmin next spring. I'm not spending my hard earned $ on something so many people have issues with.

I have a LCX 27c and bottom reading at low depth (15ft and below) is pathetic. Practically a $ 1000 unit that works worse than a $ 50 Walmart model.
But I am very happy with it in deep water, I use the dual ducer on 50khz, and on Lake Michigan and Superior it marks fish very well even a 200ft or 300ft or more.
Comparing the 2 frequencies on depth of about 75ft I have serious problems with the 200khz, I already replaced a transducer, and I think the units have too much power for what we need.

Unfortunately my fishing time on these lakes is minimal and cost of unit it's still high as of now.

Next unit will NOT be a Lowrance, possibly a Humminbird.

OK. I got my unit to work very well. I downloaded the newest software version (ver 2.3) the other day and got to test the unit for some 9 hours on Tuesday. Since I was working a weedline, I also set the upper and lower limits (0 ft. and 25 ft.), which I believe made a difference. The unit only lost track of the bottom a few times. However, only the depth READING was temporarily lost (regained within 10-20 seconds at worst). The sonar never stopped pinging (or even slowed down or stuttered). So, the graph was still reading bottom correctly the entire time. I am happy with this unit now. I have at least some renewed faith in Lowrance for the time being. We will see how long that faith lasts...

Thats too bad Valv, I'm glad I checked on here. I was about to pick up a 27C but much of my fishing is in the shallows so i guess that would be overkill. I'm looking for a large screen Sonar/GPS combo.

Will keep looking for input as these are dang spendy.

The new software versions have corrected many of the problems, and by turning down your ping speed you can clean it up pretty good. Maybe not all the time or in every situation, but not too bad. You quoted one of Valvs earlier posts, in his last post he said he had the unit working better.

Lowrance has a new line of units coming out early next year, high definition models which convert the signal to digital, and they say they won't have these problems with the new units. I've seen the demo units and they are sweet. Hopefully their performaance on the water is as good as they say it will be.

I updated the software on my 520, and it got worse. I started losing the depth reading for minutes at a time over 30 fow with NO weeds anywhere in sight. At one point I lost depth for over 15 minutes for no apparent reason; the graph told me I was in 2.4 fow when I was over 20. Should I email Lowrance or what? I'm not sure what to do???

Make sure you have the latest update. If that doesn't work, try to get them to send you the original version you had on a SD card.

The original version didn't work worth a darn when weeds were present

I have the same problem here, except I have the infamous 334 iGPS.
Another Lowrance Fail unit. I still loose my position very frequently, and loose the bottom reading when getting into weeds at 10 or so feet, and it finally picks up the reading at about 17-20 feet.
The 334 was a 1 year production, probably because the GPS didn't work. It should have been recalled. Then they replaced it I believe with the 520, and the thing can't take a bottom reading in weeds.
For $650, these things should work. My next one will not be a Lowrance.

I agree, they are just so user friendly, and for a while where the only ones that could take most of the lake cards. Now it's not the case but I really don't want to spend another $600 for a different unit. Even if the unit is out of warranty, they should really stand by it and either replace or fix, at no charge, those that are not working properly. As consumers, when you spend that kind of money, it should work, and flawlessly at that! If not, it needs to be fixed, period

There is now a new Beta update 2.4.2 that is for people like me having severe issues.

That didn't work either. I lost bottom for over 30 minutes the other day and I was in 27 fow at the time. I am working on trying to get it fixed but I am out of warranty and they tell me I need to pay for the repairs which I find to be unfair. We'll see what happens.