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HP 41CV gone nuts - Richard Carter - 03-14-2009

My venerable HP 41CV seems to have gone crazy. It started by displaying ?.?.?.?.?.3 when I touched the "3" key. The same thing would happen with the "6" or "9" key. I tryed to reset it by touching the Enter, left arrow, and "On" at the same time. The more I messed with it the more keys that would not function. At time the only thing it will do is to display "10.0000 CC" for about 10 sec. and then off for about 1 sec and then repeating this cycle.

Any help in solving this would be greatly appreciated. I would love to get my old calculator working again.

Re: HP 41CV gone nuts - db (martinez, ca.) - 03-14-2009

first, a question: did you unplug any peripheral or twist the body -with the calculator on- just before this started?

second, something that steve from austrailia posted on 24 Mar 2001,

Reseting an HP41

Quite often people post questions in the forum asking how they can reset their HP41 with or without losing the programs.

It seems that HP41's do tend to lock up more than we'd like to think they do, especially when turning them on the first time for a while, or when connecting some odd peripheral.

Perhaps it's static, perhaps it's the ghost of long forgotten TI calculators extracting revenge? I don't know.

Anyway, here is a list of things you can try to reset the calculator. Note that these are not my ideas they come from an excellent book "Extend Your HP41" by W Mier-Jedrzejowicz. I recommend you get a copy!

Following is a slightly updated copy of something I posted in the forum some time ago, and that I refer people to. However it's probably easier to find here.


In the book Extend your HP41, section 4.1, a number of methods are given to revive a calculator that won't turn on.

1) Press backarrow and/or shift to see if the blank display is caused by alpha blanks in the X register. To see how deceiving this is, turn on your HP41, press Alpha, then Shift STO . X, then alpha. Turning the HP41 on and off will appear to do nothing. Quite evil!

2) Press on then backarrow, then on, then backarrow a few times, pausing about 10 seconds between keystrokes

3) Remove all modules and try again (there's also mention of the use of an AM radio here too, as well as chacking for dirty battery terminals, flat batteries, and incorrectly inserted batteries). When the HP41 is active it radiates some RF and an AM radio (remember those?) not tuned to a station can often pick these up. The sound will change when the calculaor is doing different things, and thus you can tell (maybe) if the calculator is turning on, even in the absence of a display)

4) IF YOU HAVE A NEWER HP41, try pressing backarrow and enter then on, then releasing all three. The newer HP41's have a keystroke that does sort of a soft-reset invoked by this combination of keys. BEWARE this will cause a hard reset (losing memory) if tried on an older HP41

5) If you have a wand try reading some barcode. Reading barcode will turn on the calculator. It will also tell you if the batteries are supplying power by checking for the red light!

6) Try pressing R/S

7) Attach a card reader and run a card through it. This will also turn on the calculator, but be careful of the card you choose because it will be read. Actually on this point using the first card of a WALL set (if it reads) will allow you to hard reset the calculator by interrupting it. If your batteries are flat, the card may stop part way through -- change the batteries and reinsert the card reader.

8) Take out battery and reinsert. then press ON a few times. This also seems to reset the calculator, but this may have been the reason why you lost control in the first place! This will also clear the date and time if you have a CX or a Time Module.

9) Obscure Crashes due to errors in the buffer error (typically after synthetic programming mistakes) have equally obscure methods to recover from them.

10) memory lost (aaagh!) As per the manual, hold the backarrow, press and release the ON button then release the backarrow. This will alledgedly work if the calculator can be turned off, so strange crashes may be due to the calculator not being able to be turned off Hmmmmm.

11) take out batteries for a LONG time OR insert batteries the wrong way (using old batteries) (POOR ADVICE IN MY BOOKS), This discharges the internal capacitor that maintaind the HP41 battery. The HP41 is protected by reverse polarity by diodes, so this shouldn't damage the HP41 OR short the battery terminals (place wire or foil over the gold connectors. It's the outside two that you need to short, but you can connect all of them without any problems). I prefer this because there's no chance of killing the calculator. Either way -- 15 minutes is advised. I actually used the reverse battry approach on a CV in the early 80's and it worked (I only left the catteries in that way for a minute or two though)

12) Really nasty. The sugestion is that the battery may be dead or dying, or perhaps there's a bad connection. But you would have tried new batteries first, right? Apparantly in older HP41's low batteries can cause the display drivers to fail to synchronize. A recommendation is to take the calculator apart and leave it that way for a while! -- I told you it was nasty.

13) Even worse. Send to HP to get it repaired.

I used to have a card with an autoexecute program on it. The program was simply STO c. That worked for me once too. It is actually mentioned in step 10 in this book too.

Good luck.

Also mentioned (in step 12) is to put the calculator on a hard surface, lift up one end about an inch, and set it down fairly firmly. I hav also heard "drop one end about an inch" as an alternative. I'm not advocating this either.

I've found that it may also be worth squezing or gentley twisting the calculator. This is especially true if there are some intermittent faults. If this makes any difference, then it points to bad internal connections, a problem which is reasonably common.

If the calculator rattles and seems to hace some loose plastic inside of it, especially if it looks like it's been dropped or opened, then suspect the internal posts as being broken. This will eventually cause problems as the tension proveded by these posts holds internal contacts together

Re: HP 41CV gone nuts - Karl Schneider - 03-15-2009

Richard --

Here's a story of getting my dysfunctional HP-41CX running again. To use my methods on an HP-41CV, you'll need to get an X-Functions module.


-- KS

Edited: 15 Mar 2009, 4:43 a.m.