41C CPU board problem



#2

Hello, I've got a strange problem with a 41C that I'm trying to revive. The display won't display (completely blank) but the keyboard responds and the calculator can produce audio (via TONE and BEEP). My initial thought was that there was something wrong with the display. [duh].

Wrong. Upon ringing all the leads and surface connections, I tried putting in another full-nut CPU board from a CV and, lo-and-behold, the display works. So, it seems like the CPU board I've got works with respect to keyboard input, printer output, audio, etc. -- except for driving the display. Has anyone else encountered this problem before?

Thanks for any suggestions!

Boris -- bg@cse.msu.edu


#3

Boris, have you tried swapping back to the original board? My thought is that maybe you had a dry joint between the original display and board unsoldering and resoldering has fixed the problem.


#4

Dave, thanks for the response. The CPU boards aren't soldered on -- they're connected to the keyboard plate via a flexible wire mesh connector. I believe this is common to the non- half-nut designs of the 41.

The problem is very repeatable. As in, I put the CV CPU board in, the display works and when I swap it out for the C CPU board, the display stops working (but all the other functions remain!). I've repeated this process several times with the same results each time. I kept the exact same flex connector as well as keeping the rest of the parts of the housing the same. The only thing to change was the CPU board.

It's hard for me to believe that only _part_ of the main CPU chip can go south. I tried tracing all the visible leads on the CPU board and they seemed OK.

Boris -- bg@cse.msu.edu


#5

Maybe it's the power supply chip (U2) which creates the AC voltage signal for the display or the display driver assembly (U2 on the display driver PCB). In any case you'd need spare parts. Clean the connectors !!! Check, if the parts of the 41 housing are pressed firmly together after tightening the screws. Do NOT overthighten the screws !!!

Just a few tips. Please report the results.


#6

see 41cv programming glitch below, when i swapped boards the calculator once again became programmable!! is this y2k a little early?

#7

Dunno why, I read your original posting as 'you had changed the display'. Must read the question...


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