The Museum of HP Calculators
HP Forum Archive 07
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|Re: HP 67 Can it be fixed?|
Message #1 Posted by Tony Duell (UK) on 6 Dec 2001, 6:18 p.m.
Yes, most likely it can be fixed. I don't know what 'rubber film' you are refering to -- the HP67 keyboard does have a transparent polythene sheet under the keys but only to keep dust out -- it's not part of the contact mechanism.
To do anything you'll have to take the calculator apart. First make a diagram of the key positions, if you don't already have one (e.g. in the user manual). The flip the calculator over and remove the battery cover and battery pack. Use a sharp tool to remove the 2 plastic plugs at the display end on the bottom.
6 screws hold the machine together. 2 are under the plugs, 2 are under the front feet (lift them up from the outside edge -- don't try to remove them totally) and 2 are under the label at the corners near the battery comparment.
You need to peel up the label -- be careful if the appearance of the machine is important to you. Then lift off the bottom case.
Remeber the circuitry is mostly MOS, so take anti-static precautions. Wear a wrist strap if you have one, or at least touch eathed metalwork (kitchen sink?) frequently, and don't move too much between touching the eathed metalwork and handling parts of the HP67.
OK, lift up the front end of the card reader PCB (the long thin PCB down one side of the machine) to unplug it from the logic board. Move the reader PCB aside (no need to remove the wires at the back end) and then lift up the logic board to unplug it from the keyboard. Put the logic board in an antistatic bag until you reassemble the machine.
The main chassis is held to the top case by 6 more screws, Remove them and lift out the chassis and keyboard PCB. At this point check to see where the slide switch contacts are. They often stick to the keyboard, in which case detach them and put them back in the sliders (flat side down). Put the top case with keys, sliders and contacts aside. Remove the plastic frame and polythene sheet if it's still with the keyboard PCB. Note that this part only fits one way round due to the offset pegs.
Now look at the keyboard PCB. The switches are metal humps over the PCB tracks. Clean them by squirting propan-2-ol under the hump(s). You might try soaking a narrow strip of paper in propan-2-ol, sliding it under the defective hump, pressing the hump dowm, and pulling the paper out to really clean the contact.
Occassionally the metal strip the forms a row of humps breaks at one side of a hump. You can improve matters by soldering the strip down to the PCB, but that key will never feel 'right' again. It should work, though.
While the machine is apart you might want to take the sliders and keys out of the top case (don't lose any parts!) and clean the case parts and keys. And maybe replace the card reader roller unless it's been done before.
Then put everything back together.
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