Ok, you've done hard resets, probably soft resets, checked software, etc. So you've deleted wpts/trails, etc. If you haven't 'Purged' wpts/trails, then you need to do that. That will free up memory. Just because they are deleted, wpts/trails stay internal memory. Purging will free up memory and the unit's speed can usually seem to run faster. On Gen 1s, this is a major issue because there is only one menu that allows for purging and it is not documented in the manuals. Fortunately, purging is part of the deletion menus in Gens 2+.
I'm going by memory (I have a Gen 2 and 3). Go to the 'FILE' menu, scroll to Wpts/Routes/Trails, highlight, touch/press enter, then Details. I may have this a little mixed up but it should get you close enough to figure out. The screen will display how many wpts/trails and space it is taking up. Keep this in mind. Every time a wpt/trail (not sure it does this for trails) the wpt remains stored but not completely removed. It must be Purged for complete removal. Just be sure wpts/trails are safely saved to a card before purging. I am not completely sure if a hard reset removes the wpts/trails from the 'black hole'.
For example, if a unit has NEVER had any wpts and it is loaded with a 1000 wpts, then these 1000 wpts are deleted, they will show deleted on the wpt/route/trails menu screen; however, if you go to the FILE menu, click wpts/routes/trails, then details, it will show you 1000 wpts in the 'black hole'. These take up memory. This is why my GEN 1 HDS 8 'blew up'. Lowrance has updated menus, screens and documentation on this major overlooked instruction.
I don't think this is your problem, but at least it will give you more memory if in fact, you have been deleting but not purging wpts.
I'd still probably have my Gen 1s if I had known this. When fishing a lake, I only have the wpts/trails for that lake on my unit - or at least I thought, before I knew about purging, which I learned too late in the game. I have several lakes with over a 1k of wpts, and many 'safe' trails, mini trails, connector trails, etc. I fish a lot of timber so with TOW, I create safe passage, especially in low water conditions that I can use when the lake is higher.
After returning from a fishing trip, and preparing to fish a different lake, I will save those wpts/trails, to a card and computer, make updates on the computer as needed (skipping all the complicated stuff I do), then delete the existing wpts/trails on the units after safely storing that info, then DELETE them, and load the next lake's wpts/trails. BUT - the deleted wpts are still there because I didn't know about PURGE. I actually read the documentation manuals and Lowrance never had PURGE in their manuals for GEN 1. A search on the .pdf file shows no 'purge'. If I had deleted and then purged the wpts/trails, I probably would still have the Gen 1s, as they were good units. With ROTSITIN, how many more fish am I going to catch in a year's time?
I don't know if you mentioned it in your posts above, but try connecting the Ethernet cable to one of the other LSS ports if you haven't already. A good friend and I both had a somewhat different issue a while back with 'No Structure Scan'. It would work intermittently. Mine worked most of the time and his worked seldom. We bought new Ethernet cables and the issue went away for both of us - just a thought.
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