|Odd 41C Fix|
Message #1 Posted by Ion Abraham (New Mexico USA) on 1 Feb 2001, 9:22 a.m.
I'd like to follow up on my recent postings about trying to fix a couple of 41C's. I found a rather strange item that maybe some of you have encountered already.
One would not turn on at all. I took it apart and found that one of the fingers between the display board and the main circuit board had come off. So I soldered that back on , reassembled it and put in a rechargeable pack. To my great excitement, it came on with memory lost right away, and seemed to work just fine. But that's not the end of the story.
Later that evening I put in a regular battery pack (the four N cells), and the 41C started to go haywire. Strange display things, all sorts of bizarre behavior. So I put the NiCd's back in, and everything returned to normal.
Now, the service manual goes into some detail (which I haven't fully sorted out) about the voltage regulation part of the power supply. My current suspicion is that the supplied voltage of the two packs is slightly different, and the voltage regulation function is not working properly. I have not yet ruled out simpler things like bad battery contacts, however. (The NiCd pack contacts on the two outermost contacts, while the N cells touch all four).
Meanwhile, I just thought I'd ask whether any of you have seen anything like this, or have done any digging into the voltage regulation part of the power supply. If I'm right, then I suspect that a lot of the strange reset sequences (cntrl-enter-clx, etc.) that people have posted for these calculators are just trying to juggle random states of the chips, really caused by improper voltages on the board. But I don't really know, I'm just guessing here.
Any questions or comments would be gratefully received.
Albuquerque, New Mexico