Odd 41C Fix



#9

Hello all,

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.

Best regards,

Ion Abraham
Albuquerque, New Mexico


#10

If I am not mistaken, the two center contacts of the 41 battery compartment are just a 'bridge'. That is they just complete the serial connection of the four batteries. On the rechargeable pack, this bridge is internal to the pack.
rdb.


#11

Correction. Make that series connection of the batteries.
rdb.


#12

Yes, yes, I understand that. What about my main point, though? Have you, or any others out there, seen a 41C act very differently with a NiCd pack vs. a set of N batteries?

Thank you sincerely for your reply.

Regards,

Ion Abraham
Albuquerque, New Mexico


#13

Ion,

Based on my experience, I'd suspect the battery contacts. I sincerely doubt that it's an electronic problem. These battery contacts can do the oddest things, and as you yourself pointed out, "N" cells use all four contact pads, increasing the chance of an intermittent contact that can make your machine to weird things.


Viktor


#14

Dear Viktor,

Well, you were right, it looks like. I knew I should have waited until I checked the battery contacts before posting (as I originally mentioned). I cleaned the contacts where they actually contact the board, and the row on the board, and things improved considerably. It still is a bit flaky, giving Memory Lost messages every once in a while, and, in addition, the number 4 key seems intermittent. Sheesh. I was really hoping that the keyboard would be OK.

Any more suggestions would be greatly appreciated.

Best regards,

Ion Abraham
Albuquerque, New Mexico

P.S. Any of you all out there know anyone (in the US) who is currently willing to fix calculators for a fee? I am willing to be much more accomodating than the fellow who got Joe Rigdon's dander up. (I recently saw that exchange in the archives, after trying to contact Rigdon by email).


#15

I cleaned my batt contacts using some sand stick. After I painted with a conductive silver based ink and waited for 24 hour and it works fine.;)

#16

Ion,

Do those intermittent problems occur also if you're using the NiCd pack?

Keep in mind that inside the calculator there are several pressure contacts. If they are corroded or contaminated, or if the calculator's case has been damaged (e.g., cracked screwposts) and no longer holds the calculator securely together, you may get intermittent problems.


Viktor


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