Re: HP-28S Malfunction Message #7 Posted by Andrés C. Rodríguez on 13 June 2000, 5:44 p.m., in response to message #1 by R. Miller
Just some suggestiosn to think about, no warranties:
Both halves are connected by a flexible plastic "printed circuit" or"cable", that goes from the main (right) side, exits at the the lower hinge, goes halfway up thru the spine, again goes down, and enters the left side via its lower hinge. It is placed that way to reduce (or spread) torsion stress when the calculator is opened/closed. As far as I remember, the cable only has 4 traces (wires), if I am right, that is not enough for the full keyboard matrix to be connected, and so it suggests some electronics (perhaps one single and very simple chip) are located on the left side. If so, the problem with the rows of keys should be localized inside the left half, and not related to the flexible cabling. A failure on the flexible cable should affect all the left keyboard. You can look for a HP Journal article on the HP 28 (around 1987/1988) that may add some extra information. Again, this is only a unconfirmed idea. Be careful!
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