One of my biggest fears when it comes to nonliving things is accidentally damaging the screen of my TI-89 Titanium or having something fall on it. Especially given that these aren't manufactured anymore that feels like a vulnerable position to be in. So I've been in the market for a screen protector for it.

So far I've found the Guerrilla TI89SP on Amazon but there is absolutely no indication of whether it is a cheap transparent sticker that incurs no meaningful protection or an actual solid glass product. Should I just DIY my own screen protector using some very transparent and scratch-resistant plastic?

Another thing about the screen: what is the general timeline for ribbon cable failure? Surely someday a blank row or column will manifest itself.

Another concern: the keypad. Do these things have a history of getting their keys stuck or mushy over time, or keys randomly deciding not to register after enough use?

My final concern: The sliding back cover. For a couple of reasons I got a new one from an old TI-84 Plus (it fits perfectly on the 89T) but the "new" cover has been used a lot and is quite loose. Should I break out the 3D pen and extrude a tiny bit of plastic onto the sliding cover to make it stay on the calculator better?

Nevermind about the sliding cover thing! Pro tip, just put a few layers of tape on top to make the friction come back again.

Neither my TI-92 Plus nor any TI-89 Titanium of mine has developed ribbon cable failure. On the other hand, I did try to get a Voyage 200 that came with pretty bad ribbon cable failure (& then returned it, because it was supposed to be brand new).

My TI-92 Plus had its up arrow key fail eventually, & when I got a for-parts TI-92 to swap out the keypad membrane, I found out that the D-pad had an extra piece of plastic that had gradually worn a hole in the membrane at the up arrow position. That was with years of playing Tetris (among other things), so they seem to be quite durable even when part is defective (!). On the other hand, when I swapped out the membrane, the one from the TI-92 turned out to be way less mushy...so they do get mushy (but still type fine) over time.

My first TI-89 Titanium had its case catastrophically fail (one battery contact's plastic backing broke through, & then when I tried to investigate, all the screw posts broke off). Both it & the replacement developed occasional doubled keypresses that developed into annoyingly many doubled keypresses (enough to make playing Tetris frustrating rather than fun). When I recently got a third one, I found that its keypad felt way nicer, so I guess they do get mushy as well in addition to the doubled keypresses (unless TI just made it better...it felt better than any other new TI graphing calculator except the TI-84 Evo I just got, so maybe it is just they improved the keypads...better even than my TI-84 Plus CEs were when brand new).

I pretty much only use the slide cover on mine when changing the batteries, so none of them got loose. It felt more like the battery doors might wear out, but only the first one did (at the same time as the other case failures, so maybe all one manufacturing defect). But never using the slide case did mean that the first two got pressure spots on the screen from being in my backpack, so there is a tradeoff here.

My second TI-89 Titanium had its LCD start leaking at one point, & I had thought to put it in the freezer, but someone said they had done that with an LCD once & had it leak way worse, so I instead put it in the heat coming out of the back of my desktop, & after a while it made the leak reverse. After this it never recurred, so it is possible this was a fix. (I did also pray about it, so I cannot guarantee it was not due to divine intervention.)

I got my TI-89 Titanium used, and the screens are prone to getting screen burns, but I haven't noticed anything with the buttons.

Assume the screen protector is just a plastic film, more so with the packaging showing what seems to the protector in a curled position. Manufacturers will absolutely take every opportunity to advertise if it's glass. They do make glass protectors for LCD viewfinders on cameras though, so there might be one that somewhat matches the dimensions of the TI-89 LCD opening.

TI-89 ribbon cables use a much more mature bonding method than on the TI-83 Plus and earlier. As long as they don't experience temperature or humidity extremes, they should last several decades. I've even once put a concerning amount force on the ribbon cable of my TI-89 by accident and it's still flawless. There's still a chance, albeit slim, that it starts deteriorating regardless though, see eBay for examples.

Keypad won't deteriorate with normal use, but still very vulnerable to spills and battery leakage. Immediately take it all the way apart, especially the rubber mat over the keypad contacts, and let dry if anything spills on it. Best to skip alkalines entirely and use Ni-MH or those fancy lithium AAAs to avoid leaks.

Edit: just noticed the first reply, genius idea for rejuvenating slide covers. Going to try that out on my own calculator too.