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HP 41c Locking Up - Printable Version

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HP 41c Locking Up - Art Wong - 09-13-2000

Hello all,

As a student, I was one of first HP 41c buyers. It served me faithfully through university and beyond. Now my children are going into middle school and want to introduce them to RPN.

I pulled my unit out added new batteries and it powered up and worked fine for 20 minutes. Then it started to freeze. By freeze, it doesn't respond to key strokes or On/Off switch. I must take the batteries out, wait for 4-8 hrs and try to insert them again. Sometimes it will work for a few minutes but then lock up.

Any suggestions on how to revive this antique.


Antique!?!? - Steve (Australia) - 09-13-2000

Antique!?! You're talking about the finest piece of calculator technology ever developed!


Some things to try:

1) Are the battery terminals clean? If you removed old and leaking cells, there may be a problem withthe contacts, or perhaps worse inside the calculator.

2) Could the calculator have been dropped? The HP41 is not known as the most rugged calculator, dropping can break the posts that hold the calculator together (and this pressure ensures that connections remain between some of the internal boards (although the earliest 41C's wer a little more rugged in this respect)

3) Does it lock up if you just execute an ON instruction and leave it sitting there? This will prevent it from turning off, and by not touching it, you are not doing things that could cause any problem with broken connections to happen.

4) have you done a MEMORY LOST on the calculator after waiting for 4-8 hours, or just let it start up again.

5) dod you know that you can short across the calculator terminals (not the batteries!) to reduce this 4 to 8 hours to a couple of seconds (or maybe minutes).

6) was it ever taken apart to install (say) a speed up option? if not done properly, then this may have damaged your calculator (the posts maybe if it was overtightened).

What is the serial number of this calculator? If you really did buy it very early on, then you may have an interesting calculator.

Does it have gold balls in the charger hole (for want of a better description)?

Re: Antique!?!? - Art Wong - 09-13-2000

Hi Steve,

Don't get me wrong I am a BIG fan of the 41c. I wore it proudly on my belt as a prehistoric geek through engineering school and into work. I did more on that calculator than my Apple II computer. Just wish I could bring it back to life.

Yes it has the gold balls as contacts and the serial number is 1939A00407. Don't know if this represents the 407 th unit made.

To all your other questions it is in mint condition; never dropped, never opened, contact were cleaned, did short out the gold balls to shorten the discharge time. In fact I applied foam weather stripping to the sides to provide better grip and on the bottom to even out rough surfaces.

I tried to use it again today and had to plug in and out the battery pack many times before the keys would respond. After a couple of 4-5 calculations it froze again. Battery voltage is 5.92V.

I hope it hasn't died after years inactivity.


Re: Antique!?!? - db (martinez, ca.) - 09-13-2000

steve; FMI could you explain #3, that one is new to me, and i am an antique. thanks.

Re: Antique!?!? - Steve (Australia) - 09-14-2000

OK, the reason I suggested using the ON instruction and leaving the calculator sit there is that the
lockups may be caused by the action of pressing the keys twisting the calculator, or somehow moving
things internally.

If the calculator is content to sit there without being touched then this is some evidence that the cause is
something mechanical. (like broken posts, or a broken wire, etc.)

I would also try to cause the problem by pressing the PRGM, ALPHA, or USER keys firmly, or pressing
other keys firmly. Then I would pick up the calculator and see if twisting it causes problems.

If these things DO cause the problem, then I'd pull it apart and look for the common problems...

Oh, and with the serial number 1939A00407 (which means 407th HP41 produced in the 31st week of
1979) there is a possibility that this calculator has ALL bugs. This makes it (potentially) a rather special

To test this, enter


STO 00


if this results in the BAT annunciator displayed in the display, then you have a bug 3, and that generally
indicates you have all bugs.

Bug 3 was removed in the FDE ROM revision that was installed in serial numbers 1936 to 1952, but
the older DDE revision exists in some 41C's up to serial number 1940 (1926 is the earliest).

Even if you can't get it to work perfectly, you may find that it will fetch a good price on ebay -- possibly
enough to get you a CX.

I purchased a 41C from a guy in Canada quite a while ago that had all the bugs. I found that when it
arrived in Australia it had rather obscure symptoms -- none that required removing the batteries for
several hours -- but it certainly did turn itself off at odd times. Mine was a rather simple job to fix, and
it is now my favorite 41!

Oh, and mine is 1937A002XX -- only 2 weeks younger than the 41 in question. Which rases the question, who has the earliest calculator? I've left you guys more than 11 weeks to beat me by.

Re: Antique!?!? - Viktor Toth - 09-14-2000

My "allbugs" 41C has serial number 1936A00XXX.


Re: Antique!?!? - Art Wong - 09-15-2000

Tried your bug test and yes the BAT flag came on.

Playing with the unit some more I find if I insert the battery pack just right it will come on for a few minutes before locking up again.

BTW, though I am a Canadian I bought my 41C when visiting relatives in San Francisco. My original intention was to buy a 29C but was blown away with this LCD, alphanumeric, expandable portable computer. I ended up getting my cousin to drive me 3 hours to a store which had one in stock.


Springs? - Steve (Australia) - 09-15-2000

Glad to see it's got bug 3!

If you think that the problem is the batteries, then check the following:

1) that the contacts really are clean in the calculator. Nice shiny gold is the good colour :-)

2) that the batteries themselves are clean. Unusual in new batteries, but you might try rubbing both ends of the cells vigorously with a dry cloth (on your jeans?).

3) A more significant possibility is that the springs on the battery pack are dirty or compressed. Make sure they're nice and shiny and extend almost a third of the way up the cavity. When you place batteries in the pack, they should be forced out of the pack by about 3 or 4 mm.

However, although I'd like to think that the problem is this simple, it is possible that it's a red herring. Movement and flexing of the calculator as you insert and remove the batteries may be moving something else that is the actual cause.

Good luck!

Re: Antique!?!? - Gianmaria (Italy) - 09-17-2000

Steve, just to reply you I have a clean and perfect 41C with 1932A000453.

It's complete with box and all manuals, I bought on Ebay a couple of months ago for less than $40 as broken calculator, I only cleaned it and replaced cell with another fresh and then I enjoy myself with the BAT annunciator pop-up...