The only person I know that I could swap head units with is working overseas until July. I'd like to meet up with someone at the lake and see what happens but I really want to do it this week. I'm trying to go to OK this weekend and want it fixed before then.

I know of several units (1197's) where the DI and SI went out but the 2D and mapping still works. I have one. It was going to cost $500 to send it to the factory. I didn't want to invest that much in an old unit.

However, I still use the 1197 for 2d sonar and mapping. It will show the DI and SI networked from another unit though.

THAT'S not what I want to hear! I JUST got this unit a few months ago while I was in the hospital and was really looking forward to my upgrade which worked for several hours! Hopefully this is NOT the case.

And the news is not good. Thanks to 44 Diesel for coming out to help me diagnose that my head unit is not working properly. Sure did like his new Helix 12 though!!! It looks great with my transducer painting a beautiful picture. Unfortunately mine still doesn't with my transducer or a different one. So gotta call HB in the morning and see what the damage is.....at least I still have 2D and GPS for right now?!
It's seems like this might be a fairly common issue with these units. I've heard from several people now that this has happened to.

There's been some deals on units in the forum lately. You can probably buy one of those for what it would cost to repair but then have a second screen to dedicate to mapping.

I was told by 44 Diesel about how much it should cost to get it fixed by Humminbird, at least about what he remembered paying for same situation. He said that HB sent him a refurbed 999c HDSI in place of his 998. If that is in fact the case, between the cost for what I originally paid for the now broken unit, plus the cost for the warranty fix, I will get a factory refurbed unit for the cost of a new 999 from Cabelas. Not that it is a great deal but I don't know if I want to go that route or spend ANOTHER large chunk of change for another used unit......
Will it display SI from another linked unit, or should it still be able to even if it isn't able to read an SI signal on its own?

Mine was still getting si,di from another unit through the network. Just would not read si,di when directly connected to the hdsi transducer

If you come near Arlington for anything, I have linked units that you can connect to and see if you can get it to read SI from that

I'm going to live with it for now. I really don't want to spend extra money on it at this point. My buddy is upgrading his setup when he gets back from overseas so I'll buy his 1199c HDSI and 859ci HDDI. My plan is to install my 998 in the dash and use it for dedicated GPS and 2D. I'll probably also use the DI from the 1199 alongside the 2D and use the 1199 as dedicated SI. I'll have to get a hub so I can link all 3 together for GPS and waypoint sharing.

Try running a power line directly to the battery. If the unit isn't getting enough juice or is spliced and getting interference, that could be your culprit.? My 597 CI HD DI was doing a similar thing as yours. 20' strip of cable at Wal-Mart for $6. My DI would work well, and then fade out, off, or to stripes. Also, make sure the power cord in back is getting a good fit.

If your maps and 2d sonar are still good, see my post above. The unit will need to be sent to HB for repair.