HP 41CV

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.

Roadhand
Thanks for the great advice.
It is working now. I removed the surveying chip and the batteries. Reinstalled the batteries and it works. Plug in the chip and it quits. Unplug the chip and it works. Pretty good indication something is wrong with the chip module.

Thanks again for your help.

John1Minor2

I've fixed a lot of 41's over the years and yours sounds typical. The battery contacts and the module "tabs" are on the same connector "block" that relies on an internal foam sponge to make contact with the circuit board of the calculator. Going longer than 30 years now that sponge is well past due for a squeezing. Here is what you do:

1) Remove the batterys, all modules and all module covers.
2) Place calc flat on its face and remove the 4 rubber feet at each corner on the back of the calc.
3) CAREFULLY using a philips head screwdriver remove the 4 screws from the corners that were under the feet. Carefully I say because the screws are sheet metal type screws that thread into plastic posts on the top half of the calculator. They WILL break and then you've got to fix that. In fact yours may already be broken adding to the problem that the lower half of the calc and the top half of the calc no longer fit together tightly.
4) Screws out lift the bottom up and flip the bottom over. Careful as their are 2 wires to the "speaker" that is usually taped to the inside of the bottom of the calc.
5) Lift up the gold "block" and give it a good squeeze to make it taller. Q-tips and rubbing alcohol are good to clean the contacts of the circuit board, the contacts of the "block" and the battery contacts while you are doing it.
6)Put it all back together and do NOT tighten the screws so tight you break the posts!
7) Enjoy your 41 for another 30 years!

Thanks Dave
I have the calculator working now thanks to Roadhand's earlier post. The Survey module appears to be bad because when I plug it in, the calculator quits. Could this problem be solved with your sponge treatment?

John1Minor2

You're very welcome. I can't take credit for "knowing" how to fix it, just where to look. http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/forum.cg i">TheHPmuseum

"Could this problem be solved with your sponge treatment?" It surely can't hurt, what have you got to lose, but first of all have you tried the module in any of the other 3 ports? Do you have access to another 41 to see if the problem follows the module itself?

Hey Dave
Now I feel rather foolish! I put the survey module in a different port and the calculator keeps working. Maybe it isn't the module after all.
Thanks for the suggestion. I really should have thought of doing that myself.

John1Minor2

Has anyone heard from Fixthatcalc recently ?

Cheers

Derek