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David Shenk´s 'Soldering Upgrades in my 42s': any success? - Printable Version

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David Shenk´s 'Soldering Upgrades in my 42s': any success? - Vieira, Luiz C. (Brazil) - 10-23-2009

Hi, David;

just to ask if you succeeded soldering the 32KRAM IC.

Best regards.

Luiz (Brazil)

Edited: 23 Oct 2009, 12:54 p.m.

Success! - DavidShenk - 10-24-2009


Yes! I just finished tonight and it works! Well, it didn't work initially. I had trouble getting the 42S to turn back on, then finally it said "memory reset" but then froze up. I took the batteries back out and found a few places that needed some touch up. I also went back over the jumper that is removed to make sure it wasn't making any contact. That seemed to do the trick and it is now working properly and reporting it's newly found memory.

I had ordered some new soldering tips as well as a fine solder wire, 0.020 inch. I ended up doing it your way and used the fine wire and the tip I was having trouble with. That method worked great for me. I also have a magnifying hood that is a must.

Thank you for all of the help and hand-holding. Thanks also to the others that had ideas. I am looking forward to doing some testing with the other soldering methods.


Re: Success! And good luck! - Vieira, Luiz C. (Brazil) - 10-24-2009

Hi, David;

I guess I speak in the name of all others when I say that the best 'reward' (if I can say so) is the success of all our friends and contributors, here. I feel sincerely happy for you as I felt the many times I succeeded bringing calculators back to life or after an upgrade. For these days I´m building my second MLDL2000, and it´s been actually fun. If you have not seen any of these yet, please, have a look at the official site and be my guest here (my MLDL2000 assembly) I added three new pics showing the internal connector with some more details.

As you have any news or needs, please, let us know.


Luiz (Brazil)

Edited: 24 Oct 2009, 1:33 a.m.

Jumper and HP42S "Memory Clear" versus "Machine Reset" - Geoff Quickfall - 10-24-2009

Yes, I just did my three and each one had a power up problem:

one machine said "memory clear" and froze.
Turned out to be a cold solder joint on the
just installed 32K chip.

the other two needed "time outs".
Both had the batteries removed and then the
battery contacts shorted. This resulted in
"memory clear" followed by "machine reset".

All three pass the diagnostics.

An interesting note about the jumper you remove. It actually did not need the solder to complete the circuit as there is a bridge trace joining the two sides. Contrast this with the jumper that you have to make. It has no bridge. So it is not enough to remove the solder but you have to physically remove the bridge trace.

The jumper with solder removed and the bridge trace apparent while the jumper to be soldered has no bridge trace:

New jumper soldered and the bridge trace physically removed from the old jumper:

Edited: 24 Oct 2009, 2:46 p.m.

Re: Jumper and HP42S "Memory Clear" versus "Machine Reset" - DavidShenk - 10-24-2009


I wasn't expecting the power up problem, but it looks like I'm not the only one. After I went back over everything to make sure it was soldered correctly, I did short the battery terminals as well. So I'm not exactly sure what corrected the problem, but at this point I don't care.

It's interesting that the jumper is permanently connected on the board like that. I wonder why they bother to blob solder on it during production since it's already connected.

I may do the crystal mod as well, but I didn't order any of those when I got the 32K chip. Apparently you can have both crystals in and switch between them. That seems like a very cool idea. I don't yet have a printer, but I would like to get one and would like the calculator to still work with it.


Re: Success! And good luck! - DavidShenk - 10-25-2009


I appreciate the friendly atmosphere here. It is obvious that everyone is dedicated to their machines and getting the most out of them.

Thank you for the link to the MLDL2000. I hadn't seen any of that before. The next 2 calculators I really want to get are a 41CX and a 67. I have done some machine language programming in the past, so this might be a fun extension of my 41. I finished a program for the 42S a while back, but have been lazy and have not submitted it here yet.