HP-41CV dilemma



#27

Hello all.

I pulled my old 41CV out of mothballs after three, yes three years. Well, my first action was to charge it. Does the 41 operate while it's being charged? If so, although it's an hour, the 41 won't turn on. Or, do I need to wait a bit longer to see if the 41 can be functioning while it's charging? Or, if it's the batteries and they're so deeply depleted, is it the 41 cannot operate while charging?

What could be the issue with my 41? If there is a glitch, is it fixable?

Edited: 12 Mar 2012, 1:17 p.m.


#28

I do not know the 41 specifically but if it's like all the other calculators except the classic (35, 80 etc.) that uses the battery for voltage stabilization. Then yes, it's absolutely possible the batteries are so depleted that it won't turn on. Have a little patience and suddenly it will.

That said. Keep a good eye on the rechargeables. Long time stored can suddenly leak when charged and that of course needs to be cleaned immediately. It depends on how new they where before storage, how hard they're charged for the first times afterwards etc. A lot of factors.

Or just buy some alkalines - isn't it N sized it uses?. Where I live you can get brand names N size cheap on the internet. In photo stores they'll rob you.


#29

Well, thanks. I just bought the N-cell holder a few days ago. In the meantime, I'm giving the 41 a few more hours to charge (although, by now, it's been 2 hours, 15 minutes). Which brings up another question. It feels that the charger plug can go into the 41 both ways. Or must the plug be specific as to if it's face up or face down down?


Edited: 12 Mar 2012, 2:24 p.m.


#30

The charger output is AC so don't mind.

The 41C sometimes has a glitch and won't turn on, even with new batteries. There are a few ways around, one is shorting the battery terminals with batteries taken out, of course. A master clear (ON+backspace if I'm not mistaken) may help. It's always a good idea to take out all modules while trying to resurrect a 41C.

#31

With the 41 the charger plugs directly into the battery so the calculator feeds off the battery never directly off the power supply.

My experience is that HP-41C rechargeable packs don't handle storage all that well and three years may well have killed the cells. How old was the pack when you put the calculator away? If it has never been rebuilt I am going to assume that it is quite an old pack and rechargeable batteries don't last forever and they particularly dislike full depletion.

If you can get the thing to turn on with alkaline batteries and you want a rechargeable pack run down to your local Batteries Plus and they can install new cells for you. Hope this helps.

BTW, I assume that you checked the output from the charger?

Cheers,

-Marwan


#32

Quote:
...With the 41 the charger plugs directly into the battery so the calculator feeds off the battery never directly off the power supply...
This is only true in the case of the two pin 82120 pack. The original design three pin pack is similar to the classics charger arrangement where plugging in the charger connects the calculator to a separate 5 volt dc source while the batteries charge from a separate constant current source with the battery disconnected from the calculator.

#33

I must admit that I have never seen or even heard of this other design. I know that originally there were pins in the calculator body that were to be used for an external power source. These pins (I had them in my original 41C) later (very rapidly) went away and were replaced by the 2 pin packs with which I am familiar. I had never heard of a 3 pin design until today.

If someone could point me to a reference for this alternate pack design I would appreciate it. Web searches so far have come up empty.

Cheers,

-Marwan

Edited: 12 Mar 2012, 10:49 p.m.


#34

I may take a picture later today of my first, 3 prong, power pack.


#35

Thank you!


#36

Hope this helps:


Massimo


#37

Thanks very much. I had never seen one of these. It appears to have the same model number as the later 2-pin charger. Sort of funny that this model ever existed since one of the nice things about the 2-pin version was that a lot of the accessories (both printer, tape drive, disk drive, and various others) used the 2-pin charger. What charger was used with the 3-pin pack?

Thanks again!

-Marwan


#38

It's always the same adapter, in the two separated pins variety.

Massimo


#39

IMHO, the 2 pin packs are much better. The three pin packs can be converted to two pin packs, makes them more reliable.

Cheers,
John


#40

Probably, however I don't use them anymore: only N-size alkalines or NiMH rechargeables. Or, better yet, the USB port adapter...

Massimo

#41

Ah! Yes, I can see how that works. But then what is the third pin for? If one is using a 2 pin adapter why does the battery have 3 pins? Was there at one point a 3 pin adapter? What am I missing? Probably something simple!

Thanks,

-Marwan


#42

The photo is missing the important part - viewed end on, it is easy to see that the the center pin is a switch. When open, as in the charger is plugged in, the switch disconnects the battery from the calculator, the behavior is the similar to the gold leaf spring on the classics. The 10 vac from the charger goes to two different supplies, one to charge, one to run.


#43

Ok. Thanks. I see how the center pin can be used as a switch. But how does one get two different supplies off of a 2-pin charger? Is there circuitry that uses the AC supply to act as if it was feeding from 2 sources? Seems like a very convoluted design to me.

Thanks again for all the explanations!

Cheers,

-Marwan


#44

The supply is ac, which is rectified, filtered and fed to a constant current source to charge the battery and to a 78L06 linear regulator to power the calculator.

The unusual HP twist is were they substituted two zener diodes in the full wave bride rectifier to act as an over-voltage clamp. Quite clever, I've never seen this done elsewhere.


#45

Thanks! That completes all the bits and pieces. And I thought that I had seen, or at least knew of, most HP41 accessories offered by HP.

Cheers,

-Marwan

#46

You're right Randy; here we go:


:-)

Massimo


#47

Thanks for the second image.

-Marwan

#48

I don't think there ever was a 3 pins adapter.

#49

Hi, Massimo. You OK?

I was wondering about the big square cut in the middle of the two-pin female connector in these adapters. The HP97 and some 82143A printers have a small plastic guide in the middle of their AC inlet, and I used to think they were 'made for each other', i.e., to avoid other adapters to be used. Now I am also considering the square cut to allow two-pin adapters to be used in three-pin rechargeable packs.

Cheers.

Luiz (Brazil)


#50

Hello Luiz, I'm fine, thanks, and you?

Yes, it was the same adapter that could be used in both ways. I don't know why the 82120A was originally conceived this way... but it worked very well, I assure you! ;-)

Greetings,
Massimo

#51

HI.

I use some HP41 for years, and almost all of them run with either alkaline batteries OR N-size rechargeable ones (for about eight years, give it or take). I never had a working rechargeable pack, instead I have four non-working units. The charger for these packs varies a lot, and you are correct: the input is AC, not DC, so you have no polarity marks at all.

I'd give fresh alkalines a try. As you surely know, the HP41, along with most calculators with no 'ON/OFF switch key', has a toggle key: press to ON, press to OFF, meaning that it needs some minimum operating conditions to be turned ON. Or else it will be stuck in a C-MOS loop of some kind that does not allow it to wake itself up by the sensing of an ON/OFF toggle key. If the voltage in the battery pack reaches a 'level-too-low-to-operate' condition and it has, say, two bad cells, then the output voltage is not enough to power it up (can you measure it?). And if you use some fresh batteries right now it may not turn ON immediately. It does not mean it is broken, just that you'll probably need to let it rest for about 20 hours without the batteries (an overnight resting...) prior to give it a try. If it is a coconut, give it as much time as you can. Halfnuts somehow need fewer hours to recompose.

Hope this helps a bit... or two.

Cheers.

Luiz (Brazil)


#52

Quote:
HI.

I use some HP41 for years, and almost all of them run with either alkaline batteries OR N-size rechargeable ones (for about eight years, give it or take). I never had a working rechargeable pack, instead I have four non-working units. The charger for these packs varies a lot, and you are correct: the input is AC, not DC, so you have no polarity marks at all.

I'd give fresh alkalines a try. As you surely know, the HP41, along with most calculators with no 'ON/OFF switch key', has a toggle key: press to ON, press to OFF, meaning that it needs some minimum operating conditions to be turned ON. Or else it will be stuck in a C-MOS loop of some kind that does not allow it to wake itself up by the sensing of an ON/OFF toggle key. If the voltage in the battery pack reaches a 'level-too-low-to-operate' condition and it has, say, two bad cells, then the output voltage is not enough to power it up (can you measure it?). And if you use some fresh batteries right now it may not turn ON immediately. It does not mean it is broken, just that you'll probably need to let it rest for about 20 hours without the batteries (an overnight resting...) prior to give it a try. If it is a coconut, give it as much time as you can. Halfnuts somehow need fewer hours to recompose.

Hope this helps a bit... or two.

Cheers.

Luiz (Brazil)


I appreciate all your suggestions. Here's what I've tried so far.

1--Recharged the 41 for eight hours with the rechargeable pack.

2--When that was over, I tried turning the 41 on with the charger plugged in and with the charger disconnected. Both times, the 41 vdid not turn on. So, I'm thinking the pack is completely drained, discharged or cannot hold a charge.

2--I then installed the N-Cell batery chamber with fresh batteries

3--as per suggested, I tried an ON-(<-) backspace key reset. I held down both keys, released the <- and then released the ON. Did I do it right?

Although I've pressed the ON key several times, nothing has happened yet. But, the 20 hour rest I'm willing to try. Could you clarify what this means:

"let it rest for about 20 hours without the batteries (an overnight resting...)"

Are you saying I should remove the batteries and put the battery case back in the 41, let it rest for 20 hours? What exactly do you mean 'without the batteries'? Please, I need to be as specific in the directions as possible.

Thanks.


#53

The 20 hour rest with batteries out is the long way to accomplish this. The other approach as suggested by someone above is to short the battery terminals on the calculator side (far ends) with a short piece of wire or a paper clip or other metallic item. This accomplishes the same thing as the 20 hour rest with the batteries out by draining the capacitors that retain memory during a battery change. This has always worked for me when one of my calculators has "frozen".

As for how to accomplish the 20 hours rest, it does not matter whether the battery case is in the calculator or not as long as there are no batteries installed.

Hope this helps.

-Marwan


#54

So far, I've repeatedly tried the ON-ENTER-BACKPASCE resets without any success. Well then, exactly how do I accomplish that shorting trick with the paper clip?


#55

Use a paperclip to short the outer terminal within the calculator. If you look inside the calc you will see four gold colored terminals. The middle two are a "bridge" for the inner two N-cells and are not used at all by the rechargeable battery pack. You can easily see how the inner connections serially connect the inner two cells. The outer terminals are the ones that you want to short. Using a paperclip or a piece of wire short out these two terminals while pressing the "ON" key 2-4 times (pressing on is probably not required but it is the procedure I have always used). After this try inserting the alkaline batteries to see if the unit powers up. Sometimes, with a severely hung unit, I have had to repeat this procedure a couple of times but it has invariably worked for me.

Hope this helps and good luck.

-Marwan


#56

How do I short out the terminals. I'm new at this so, please explain this maneuver. Am I supposed to lightly touch the terminals, brush tem? Just what am I supposed to do? Like i said, I'm new at this so, please explain. Thanks.

As an added note, what I've noticed is that when I go through the ON-ENTER-<Backspace> with just right coordination of pressing the keys simultaneously, several segments of the LCD will flash on & off quickly. Does this help you figure out what's happening with my 41?

Edited: 12 Mar 2012, 10:44 p.m.


#57

To short out the terminals connect them together using the paperclip. Just hold the paperclip against both outer terminals simultaneously while pressing the ON key. If using wire it helps to have three hands to accomplish this but since a paperclip is stiff it is a relatively straight-forward procedure.

#58

...a visual check in the batteries contacts for residual leakage and other material, usually a greenish stuff (residual from chemical reaction) all over the contacts surface. Use some soft tissue moistened with water-free alcohol. Do it carefully, avoiding to bend or to tear off the contacts, for they are thin, golden plated copper sheets.

Success!

Luiz (Brazil)

#59

Well, after I tried the short-circuiting idea. my 41CV still won't turn on. So, unless I've not tried everything, perhaps there's a logic board issue. Unless there's a reset technique I haven't tried, perhaps my 41 is very ill. Any thoughts?


#60

Hi.

Can you check if the upper and lower half parts of the calculator case are gap free, firmly pressed against each other? Under each of the rubber foot there is a small Philips screw, and the plastic posts in each side of the modules/batteries contacts assembly may crack and leave a gap that is enough not allowing the batteries voltage to reach the main board. If you place your HP41 over a regular table and slightly press the calculator down (try the edges between the toggle keys and the first roll of keys in the keyboard) while trying to turn it ON, chances are it will react if this is the problem.

If you need more info, let us know.

Success.

Luiz (Brazil)

#61

Matt,

I recalled and was able to find a list of 10 things to try if a 41C won't power on:

Quote:
Re: HP-41CV Won't Power On

Posted by Steve (Australia) on 14 Sept 2000, 9:11 a.m., in response to HP-41CV Won't Power On, posted by Philip Elliott on 14 Sept 2000, 8:06 a.m.

Try the following:

1) turn on, press backarrow or shift (display may just contain alpha blanks.

2) press on (wait 10 secs) press backarrow (wait 10 secs) press on (wait 10 secs) press backarrow... (do this a few times)

3) check correct orientation of batteries, new batteries, dirty battery contacts (springs too)

4) press backarrow and enter then on, then release all three (a few times) or do this with enter and on. Or do it with R/S pressed (in case you have an auto execute program that does an off).

5) plug in a wand and try reading some bar code. or try plugging in a printer and pressing the print button (then press ON and try it again). Printer will print X register when HP41 is on, even if display is dead (low power or just dead)

6) attach card reader and try to run a card through it (try again after pressing ON)

7) press ON remove batteries, press ON again, insert batteries press ON, remove batteries...

8) try to do a MEMORY LOST reset on the calculator (backarrow and ON)

9) short battery contacts on the calculator with foil for a few minutes then reinsert batteries and try again

10) take 41 apart and put it back together again :-) (actually this will do a reset of the calculator too, but you've got to be a little more careful.



edited to emphasize that I do not claim to have developed the steps, just passing along information.


Edited: 13 Mar 2012, 3:41 p.m. after one or more responses were posted


#62

I have actually managed to do #10 (take apart and put back together) WITHOUT losing memory!

Cheers,

-Marwan

#63

I've tried all of the keyboard and battery gymnastics tricks on this one but, no success. At this point, the foil trick might be an option but, unless it's different than the paper clip short-circuit, I'm willing to concede a logic board malfunction.

If the foil trick is different than the paperclip short-circiut, as I'm no electrician and not very coordinated, please give me EXACT step-by-step details on how to perform the foil option.

Any thoughts?

Edited: 13 Mar 2012, 7:46 p.m.


#64

It might be time to disassemble it and check for cracked/broken screw posts, and clean the connector strips between CPU board and display/keyboard.

Cheers,
John


#65

YIKES!! And I'm no electrician. Is there someone here I could send it to to investigate? I'd be willing to send my little friend to one of you here who is more skilled than I to perform the surgery.

Edited: 13 Mar 2012, 8:41 p.m.


#66

Hi.

Try contacting fixthatcalc, but they have temporarily suspended accepting new repair requests. Check the link and you'll understand it batter.

Cheers.

Luiz (Brazil)

#67

Are you aware of Fix That Calc? It is run by Randy who frequently posts repair and technical advice here. Apparently he was temporarily not accepting work, don't know what his status currently is, but you could check.

While a lot of the repair techniques require a lot of skill, simply opening a 41 to check for cracked posts does not require much skill. Check the opening instructions and repair instructions available at this site. Of course only do what you are comfortable doing.

edit - I see Luiz beat me to the punch with reference to Fix That Calc.

Edited: 13 Mar 2012, 10:53 p.m.


#68

I was just lucky... It means we all have the same information... and goals!

Cheers!

Luiz (Brazil)


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