HP-97 Key Contact Repair Adventure
Message #1 Posted by LHH on 9 June 2012, 5:26 p.m.
Well, if you have been following the chronicles, we have hopefully come to the last chapter in our exciting(?) adventure. The "Ol' 97" is happily printing and reading cards again but the keys are acting in a very unpredictable manner. Most of them are fine but some less-often-used are producing random function calls. So, it's back inside again for a look-see and a little 'spring' cleaning!
As it turns out this story is pretty short and sweet as a complete disassembly and a cleaning with O-Tips and DeOxit of all the PCB switch contact areas seems to have done the trick. I'm only posting to mention a few things to watch out for should you ever find yourself following this same trail. Here is a brief sketch of some lessons learned:
(1) When removing the keyboard assembly for further work it's NOT necessary to disconnect the ribbon cable going to the display panel. It's far easier to leave it attached to the keyboard PCB and remove the entire display assembly from the case along with the keyboard assembly. I made the mistake of doing the opposite and found it quite frustrating to get the ribbon cable reinserted into the connector.
(2) Be really careful about the board-to-board tine-connectors on the keyboard PCB. I recommend working on a smooth surface rather than anything cloth since these connectors can snag easily and end up getting bent out of alignment. This didn't actually happen to me but I can see the potential for problems.
(3) I did clean ALL the contacts on the PCB including the three slide-switch areas and then applied some thin grease to the slide-switch contact areas.
(4) Be careful and patient as there are again a number of small parts involved. In particular be sure the keys are facing down when you separate the keyboard PCB from the mechanical key assembly as each key has two tiny spring contacts which could easily be dislodged and lost.
That's about all I remember being important but I'll add anything else that comes to mind later. I hope the info in these threads will be helpful to someone else someday. I'm not sure why but I have always enjoyed the ergonomics of this calculator and it's great to have it back in good shape again!
LHH
Edited: 9 June 2012, 5:28 p.m.
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