Hp calculator (41CV/71B) startup question



#8

Hi all,

I've been a relatively short Hp calculator owner (still a student, but I've never used a Ti, always HPs for me.) and currently have the 50G in RPN mode (Used to use the 49G+, but the keys have failed so extensively, that it is a pain to enter anything).
My father has a 41CV (Really nice calculator!), and 71B that he uses.

I am curious about this, but if you take the batteries out of the 41CV or 71B for an extended period, (let's say >2 days), and then put the batteries back in, the calculator needs to sit for about 2 hours or so before it can start up successfully. Is this behavior "normal?" This is not an issue in normal usage though, because a quick battery change does not cause any problems whatsoever, and my dad keeps an eye on his batteries to make sure he has fresh ones.

Thank you!

Tadayoshi


#9

We need to know a little bit more but when I power down my 2 HP 41cx and 41C for about a year without batteries (went back to my HP 67 for the office) they start up within seconds and the ubiquitous "memory loss" on the screen.

No other problems so let us know the symptoms:

-unresponsive keyboard
-funny characters
-do you hold (memory reset) the 'clx' + 'on' after inserting the batteries

Can't see much wrong with the calculator if all functions work correctly after an hour, let us know!

Geoff

#10

Greetings Tadayoshi,

I believe the HP owner's manuals for both HP-41 and HP-71b recommend that the batteries not be out for more than 30 seconds, longer qualifies as a "trauma" and can lead to erratic operation. Anything that might cause power fluctuation qualifies as a trauma, the most common trauma would be removing/replacing a module or attachment while the calculator is still turned on. Registers can become scrambled, sometimes resulting in very unpredictable behavior.

If the calculator does not respond to the "master clear" procedure, removing the batteries for two or three minutes, reinstalling them, and then performing the "master clear" procedure on the very FIRST power-up attempt usually gets the calculator going immediately. If it does not, HP recommends leaving the batteries out overnight to insure that the continuous memory discharges.

In my experience, failure of the calculator to respond quickly is often a first indication that connections are failing. This could include failure of the calculator's internal pressure contacts, the calculator's module port contacts, or the contacts of a module or attachment. All critical contacts are gold plated, but the plating can be undermined by battery leakage, or worn away by too frequent attachment/removal of modules or accessories. Restoration of the plating would be required.

-Richard (plasmoid)

Edited: 6 May 2008, 7:41 p.m. after one or more responses were posted


#11

Thank You Richard,

That explains a lot. Currently both calculators are functioning correctly and completely, so there is nothing I could see (in my not quite so experienced eyes) that would cause any serious concern.

Tadayoshi


#12

Tadayoshi,

The manual states very few things about batteries except when replacing to observe the correct polarity. There are protection diodes in place to prevent reverse current from destroying the circuits but one would not want to test this.

The second caveat refers to continous memory. The continous memory in the HP 41C and 71B is maintained during a battery change by a capacitor which, according to HP will discharge in 30 to 60 seconds, at which time the memory containing, programs, registers and calculator state will be lost. In practice this capacitor can maintain the calculators memory for up to 24 hours as long as no keys are pressed or the 'on' switch is selected.

In some locked up calculators the procedures listed by HP in order:

1. turn the calculator off and then on.
2. hold down the back arrow key while selecting on (master clear)
3. remove batteries and allow calculator continous memory to
discharge over night

Next are users discovered procedures (used at own risk) and used only after HP's steps above have been followed to no avail:

1. reverse the polarity of the batteries (don't like that one)
2. short out the battery clips (watch for static discharge)
3. while the batteries are out, to speed up the capacitor
discharge press the on key a few times.

All of the above steps are used to clear a non functional calculator state that is being preserved by continous memory. The assumption is that whatever locked the calculator up is being retained in continous memory.

Now to your problem, never as Plasmoid states (although if you forget, don't worry) remove modules or charger/wall wart power supplies while the calculator is on. Always select off first before doing anything physical such as adding or removing modules. It is very rare indeed that the mistake of leaving the calculator on during module changes will result in a dead calculator, I know as over the last 28 years I have made that error without damage.

Merely removing the batteries and storing the calculator should NOT cause damage and a prolonged restart of the calculators as you describe. After 28 years with my 3 HP 41's and recently with my two HP 71B the process of removing the batteries has never caused a restart as you describe. Also, the 41's and 71B have been in storage for years without batteries and again start up immediately, albiet in a 'Memory Lost' condition.

When you purchased one of these calcs off the shelf they may have been sitting for a few years in the box without batteries and are designed to start up immediately upon the correct insertion of the batteries.

Also, the HP 41C, and CX manuals along with the HP 71B user manual state nothing about 'trauma' or 'start up delays' when the batteries are inserted correctly after the calculator has been sitting for a long time (at the time of purchase or after storing with no batteries installed).

So from your original post, NO, a delayed start up as you describe is NOT normal for the HP 71B or HP 41CX. They should at worst start in a 'Memory Lost' state within seconds of the on switch being selected, regardless of how long they have sat without batteries.

If the worst that occurs is the delay in start but the retention and correct functionality of the calculator is normal after that, then you are lucky. I will leave the analysis of the circuitry causing the abnormal delay in start up to the circiut gurus resident at this site.

Cheers, geoff

Edited: 4 May 2008, 4:08 p.m.

#13

This sounds like a defective capacitor.


#14

Hmm...I do remember my father sending them back many years ago for this problem. Thank you for your replies!

Tadayoshi


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