Fix for TI59 keyboard domes

[Chasfield]

I have had a cosmetically perfect TI59 for a couple of years but it came with some issues. The flex connector for the magnetic card reader had been destroyed by battery leakage so I just cut the affected areas away and now use the calculator without the luxury of non-volatile storage. The second problem was the reluctant actuation of the number 6 and 9 numeric keys - just like on my HP30b.

The TI59 comes apart really easily. The case halves are of excellent quality and have a good heft to them. They are held together by two screws and two lugs. The exposed motherboard is retained to the top case half by the card reader and a couple of small lugs, which engage the edge of the keyboard module. Four screws hold down the reader and the keyboard lugs must be gently displaced to release motherboard. Flipping the motherboard upright reveals a thin foam anti-rattle sheet that sandwiches between the key tops and the dome array. Mine had crumbled to dust and I had to tip all the key tops out to clean them properly (double-shot mouldings, by the way).

On with the key dome repair proper. The dome array is protected by a glued down plastic membrane. I didn't want to disturb this so I made a quarter inch incision in it next to each of the affected key domes. I was able to insert a small jewellers' screwdriver blade through the incision and under the dome in order to lift it slightly. I then fed in a fine copper wire, with a looped end, that could carry a very small amount of contact cleaner. I gently wiggled the wire to rake out the dome's inner surfaces. Job done.

Small sections of transparent label tape from my Brother label maker were used to cover the incisions. A piece of tailors' interfacing material was used to replace the rotted out anti-rattle foam, though the keyboard would work fine, albeit more noisily, without it.

The attached picture shows the critical stage of the microsurgery.

I like these calculators and I cut my programming teeth on the lower spec. TI57. The TI59 certainly gave HP a run for its money back in the day.