|Re: What's wrong with your HP41CV?|
Message #7 Posted by Paul Brogger on 23 May 2003, 6:27 p.m.,
in response to message #6 by Vieira, Luiz C. (Brazil)
It's a fullnut.
The behavior (it does behave at least!) is consistent, but consistently bad. The leftmost columns of keys seem to have been randomly reassigned. They seem to consistently invoke the wrong operations.
For example, the 8, 9, EEX and back-arrow keys work correctly. But the 1 acts instead like the 9, and the 2 acts instead like the EEX. The shift key turns on the SHIFT annunciator, but the next keypress will consistently result in the wrong operation. Some of the unshifted keypresses will invoke operations which should be shifted(!?!?) (For example, the LOG key shows and executes the "ATAN" function.) Some keys cause non-alphanumeric symbols to be inserted into the display.
I can go into ALPHA mode, and start pressing the keys in sequence. I don't remember what comes out (I could reconstruct that easily enough), but in general, it's as if the keys generally on the left side and middle of the keyboard are "offset" in their alpha values by 4 or five places in the alphabet, while the rightmost keys give the proper letter. Very weird!
I've chased keyboard traces and tried to see whether the "1", for example, looks electrically like the "9" has been pushed, but to no avail. Within the capabilities of my limited diagnostic resources, the keyboard and display seem to be functioning fine.
Anyway, there's no way (that I know of) that such a cross-connection in the keyboard could explain the mapping of unshifted keys to shifted functions. I suspect a zapped ROM, with a scrambled jump- or lookup-table has caused a random reassignment of key functions.
I've messed WAY too much with the lower screws, posts, and zebra connector. I've tried soldering the CPU board to the keyboard, first with wire-wrap wire, then with ribbon cable. I've brushed and cleaned, and scraped around solder pads and . . .
None of that seemed to change anything. It's consistently behaved the same, so I'm suspecting ROM damage. If anyone has any other suggestions, I'd LOVE to hear 'em!