HP30b - reluctant key

[Chasfield]

Emboldened by my recent success at fixing the the reluctant numeric keys on my Texas TI59, I decided I would attend to the similar problem affecting my HP30b, which has had a duff "2" key out of the box. It never fired on the click when minimal pressure was applied - all other keys would do so. It required a follow through, with extra pressure, before it would register. It also had a tendency to double fire when so treated.

I decided that I would dive in and try to fix it. The risk of wrecking the calc. in the process was not a problem as it was heading for the trash anyhow. B.T.W., this thing had the usual Rolls-Royce UK pricing for US imports when I bought it.

Apart from five small screws (two hidden under the rubber bumper of the rear case), this is a pop-apart device and brave use of the small blade on my Swiss army knife was required to pop the front silver case upwards out of the rear case/bezel (best not to start the popping near to the fragile LCD panel). I used a Stanley knife to split the heat stake ends that hold the motherboard down. This made it easy to rive off the melted over bits. The motherboard, complete with stuck down key dome retaining membrane, could then be lifted off the front case, leaving a rubber membrane and the key tops in place. The last part of the tear down was to peel back the white plastic dome retaining membrane far enough to expose the gubbins of the "2" key.

Here lay the surprise. I was dead sure that I would find some visible foreign body that was interfering with the click dome's action. However it was surgically clean in there. Nevertheless, I polished the contact surfaces with a WD40-soaked Q tip and put everything back together.

I didn't try to make good the ravaged heat stakes. Instead, I applied some blobs of translucent silicone such that they would retain the motherboard against keying pressure by filling the gap between it and the rear case. I won't need to dismantle the calc. again - if the keyboard acts up one more time, out it goes.

Anyway the fix worked and the "2" key now responds perfectly.