[HP-35s] Are bad keys fixable?

[Jeff O.]

Many moons ago I tore down a 35s, details here. Unfortunately, the place where I hosted the pictures went away, so there are no pictures. (I probably have the originals somewhere, but it might take me a while to find them.) Edited disassembly description is as follows:

Remove the rubber plugs in the four corners of the battery compartment, then peel off the rubber strip on the bottom of the calculator, and remove the six screws. The front and back halves of the case are also held together by five plastic catches, one in the middle on the top edge, one in the middle on each side, and one near the bottom on each side. These catches are not exceptionally tenacious; some gentle tugging at the case halves and careful prying between them will fairly easily separate the front and back.

Remove the 25 small screws that appear to hold down the PCB, but this will not free it. Close inspection will reveal that the posts into which the screws were screwed are mushroomed over at the top, just like the heat stakes in other HP calculators. Trim the posts off flush with PCB, and with a little gently prying, the PCB will be freed up. Once the PCB comes out, next is a thin rubber membrane, then the keys themselves. The keys are in two groups with a number of keys connected to a plastic frame, with the four cursor keys adhered to their own separate rubber membrane.

The front side of the main PCB is covered with a thin sheet of white plastic of some sort. There a little bumps visible through the plastic that appear to be metal dome key contacts. Assuming the technology is similar to the 30b (one of which I have torn down to the point of removing a similar membrane), that white plastic sheet is stuck to the PCB and the metal domes are stuck between the sheet and the PCB. So you might be able to peel off the sheet, clean the offending dome and the PCB, re-stick the sheet and re-assemble. Although I tore down a 30b to the point of removing the sheet, I never attempted to re-stick it, so I cannot guarantee that this will work. But if the alternative is getting a new machine, it might be worth a try.