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Recently I succeeded in getting such a NOS pack for my 19C. However, I doubt the cells in it are still "good enough" to allow me connecting my 19C to mains to charge them in the calc. On the other hand, I do not want to open the pack unnecessarily. And I lack any sophisticated electronic lab equipment. What do you recommend?

Open the pack, even if the cells are still OK, they will not last long, so you'll need to change them sooner or later.

Important advice: BEFORE YOU START! Take a bunch of pictures of the pack as it is with you digital camera, phone, whatever. make sure the pictures are clear (i.e. view them on your computer). Otherwise make a diagram of the orientation of the cells inside teh pack.

MARK the pack with signs showing the cell orientation to be sure you get it right in the future.

The pack is glued together, but you only need to use a shapr razor
to split the glue at the seams, and the whole case will simply open.

The pack has four standard AA 1.2 NiCd cells, can't get anything more standard than that.

Take out the old cells and insert the replacements making sure the orientation is correct. The pack has springs on one side pushing the cells against contacts on the 19C mainboard, so you simply insert the cells against the springs and close the pack. No soldering or anything is needed.

Close the pack, using sticky tape to hold the two parts together. Do not glue the pack as you will need to open it again.

Insert the pack inside the 19C and run through the following checklist:

1) There is an indentation in the pack on the side of the contacts. If you do not see the indentation, you have inserted the pack upside down and you will not be able to close the cover.

2) The two middle tabs (contacts) have notes on them indicating the polarity of the battery next to them (there is even an arrow to tell you that the note applies to the battery on the side of the arrow). Anyway the batteries in the pack should match the polarity notes on the tabs. I.e. looking at the 19C batery compartment (the 19C is face down) with the contacts nearest to you, the polarity of the batteries should be (-), (+), (-), (+).

Close the cover, hope for the best and power on your 19C.

---------------------------

Now to recharge the batteries, my advice is to simply take the batteries out of the pack and charge them on an external battery charger (i.e. never plug your 19C to the mains).

The advantage of this procedure is that you can now use NiMH cells that last much longer.

**vp

Edited: 21 May 2007, 10:03 p.m.

Thanks a lot, Vassilis!

I will go out to buy cells today, and keep you informed about the results. Then I propose your advise shall be stored in a more permanent section of the museum, maybe in an article. Since I will take some pictures as you recommended, you may get them from me if you like.

Kalimera sou

This is to let you know a 19C offered for parts some time ago turned out to be fully functional. It was risen from the death using a Swiss army knife, a razor, an old Sting battery pack bought separately, 4 new cells, a strip of household aluminum foil, some scotch tape, and a strip of a recent newspaper d:-)

So, how did I do this? I'll explain it commenting VP's instructions:

Quote:
Important advice: BEFORE YOU START! Take a bunch of pictures of the pack as it is ... MARK the pack with signs showing the cell orientation to be sure you get it right in the future.

The pictures really helped a lot, mostly by reassuring me I did it right. I skipped the marking. At the bottom line, most important is the orientation of the pack. And this is unambiguously determined by the PCB tabs extending into the compartment, and the indentation of the pack facing the cover of said compartment.
Quote:
The pack is glued together, but you only need to use a shapr razor to split the glue at the seams, and the whole case will simply open.

Well, this "simple" task took me quite some time and controlled brute force. The front and back sides of my pack measure 2.5mm each. Top and bottom halves feature some undercuts and were nicely glued together ... d:-/ and I wanted to use these plastic parts again!
Quote:
The pack has four standard AA 1.2 NiCd cells ... Take out the old cells and insert the replacements making sure the orientation is correct. The pack has springs on one side pushing the cells against contacts on the 19C mainboard, so you simply insert the cells against the springs and close the pack. No soldering or anything is needed.
True, almost. The original cells were spot-welded together like an "M". While the intercell contacts on the back side are perfectly established by the 2 springs found there, I needed to connect cell 2 to 3 at the front to reach 5V in total. This was where the aluminum foil came in. Took some fiddling but turned out to work fine.
Quote:
Close the pack, using sticky tape to hold the two parts together. Do not glue the pack as you will need to open it again.

Insert the pack inside the 19C and run through the following checklist:

1) There is an indentation in the pack on the side of the contacts. If you do not see the indentation, you have inserted the pack upside down and you will not be able to close the cover.

2) The two middle tabs indicate the polarity of the pack (there is even an arrow to tell you that the note applies to the battery on the side of the arrow). I.e. looking at the 19C battery compartment (the 19C is face down) with the contacts facing you, the polarity of the batteries should be (-), (+), (-), (+).

Close the cover, hope for the best and power on your 19C.


(The bold italic text indicates my modifications of VP's advice.) After all, the pressure did not suffice for a good contact in my 19C (though I cleaned the PCB tips). So I folded a paper strip several times and inserted it behind the pack.

Pictures of the different steps are available.

(Edited for better explanation)


Edited: 24 May 2007, 1:41 p.m.