I got a TI83+ graphing calculator which took quite a bit of fiddling to power up and when it did the screen displayed mostly garbage graphics but seemed to work fine otherwise. I couldn't find any mention of this problem on the Internets so I set out to find the cure myself. I found out that the flat flex cable connecting the calculator motherboard to the display module developed high resistance which caused voltage and communication drops. It only had 17 lines in total so I ripped the crappy flex out and replaced it with soldered wires. Good as new!

Now I gotta find or make myself a serial cable so I can transfer applications and play Mario on this thing :D