HP41CX - Strange turning-on behaviour

[Frido Bohn]

Since a few days I have experienced a strange behaviour of my HP41CX (halfnut version with rounded display corners):

When it is turned off, it can be turned on by pressing any key. The ON key works accuratelly. But it happened that the calculator was turned on while in my bag and the alkalines have drained. Supposedly, because some key has been pressed by random movement as the HP41 was in its softcase.

The reset mechanism does not work, as pressing CLX and ON simultaneously turns the calculator on but does not lead to a MEMORY LOST.

Has anyone an explanation for this phenomenon?





Any hint is greatly appreciated.

Thanks

[dinamarco]

These happened with a few month ago. I just changed the batteries and no matter... Never more... I can only think, in my case, it was the batteries. Regards...

[Norman Dziedzic]

I seem to recall there is a way to make a program run as soon as the calculator turns on. I believe we used this feature to terrorize each other In college to show an erroneous Memory Lost message on each others calculators.

Is it possible that there is something running that starts at power up or that mimics power off with a blank screen? If the calculator is not really off, that could explain the battery drain.

Edited: 4 May 2011, 9:22 a.m.

[Geoff Quickfall]

Hello;

Procedure ONE

1.  ensure the calculator is off

2.  hold the CLX key first, then press the ON key while holding

    the CLX key.

3.  release keys.

4.  should have MEMORY LOST displayed.

unsuccesful?

Procedure TWO

1.  remove batteries

2.  hold the CLX key first, then press the ON key. 

3.  install batteries and repeat procedure ONE.

Unsuccesful?

Procedure THREE

1.  remove batteries and short the far left to the far right

    battery terminals.

2.  install batteries and repeat procedure ONE.

Unsuccesful?

Procedure FOUR

1.  remove batteries and leave alone for 24 to 48 hours or longer!

The problem is, the status of the calculator became corrupted and since "ON" is an assignable function, all the keys may have been assigned the "ON" function. Purely speculation! In any event the processes above are meant to initiate a 'clean state' HP 41CX. The continued buggy state arises when the continous memory function (capacitor) causes the calc to retain the corrupted state.

Once you have finished I recomend and use a "LO" program assigned to the shifted R/S (VIEW) key. The code is as follows:

LBL 'LO'

SF 11

PSE

OFF

XEQ 'LO'

When you are finished with the calc turn it off with the LO function assigned to the shifted R/S (VIEW) key. This has the affect that when the ON key is accidentally pressed while residing in your bag, the calc turns on and executes (SF 11) the program residing in the active memory (LO); which simply commands the calc to immediately turn off.

Of course the next step is to terminate the LO program to gain access to the calc. This is done by turning on the calc and immediately press the R/S key. This haults the LO program midstream and allows you to manually exit the program and run whatever you want.

Cheers, Geoff

There is one more reset method but use with your own discretion. It has worked for me but as a last resort on an unusable machine that refused to reset using the above procedures.

1.  remove batteries and install them in reverse polarity.

2.  press and hold the ON key for a few seconds.

3.  release and remove the batteries and install correctly.

4.  repeat procedure ONE.

Edited: 4 May 2011, 2:25 p.m.

[Frido Bohn]

Hi Geoff,

Quote:

---

There is one more reset method but use with your own discretion. It has worked for me but as a last resort on an unusable machine that refused to reset using the above procedures.

1.  remove batteries and install them in reverse polarity.

2.  press and hold the ON key for a few seconds.

3.  release and remove the batteries and install correctly.

4.  repeat procedure ONE.

---

this very last method worked for me excellently. I did not have the patience to wait for 48 hours to possibly experience that nothing had become better thereafter.



The calculator offered some more very weird behaviour, as for example

- the clock only worked for one second and then freezed.

- the reset condition MEMORY LOST could only be obtained by pressing ENTER and CLX together while the calc was off.

- although I managed to get a MEMORY LOST the ill state persisted.

Thank you for the remedy!

And thank you all for your prompt replies.



Frido

[Thomas Okken]

Quote:

---

The problem is, the status of the calculator became corrupted and since "ON" is an assignable function, all the keys may have been assigned the "ON" function. Purely speculation!

---

That wouldn't work. The ON function doesn't turn the calculator on, it just disables automatic power-off. Also, when the calculator is off, it doesn't scan the keyboard, it only responds to the ON key.

[Geoff Quickfall]

, it has been awhile since I have played with the 41. The ON function cannot turn the calc on when assigned.

Thanks Thomas!

Geoff

Again speculating, could it be that the calc was not turning off? In any case, try the above mentioned resets and let us know what happens.

I remember being tricked by a fellow student that accessed my calc and using alpha, the sf 11 trick and a short program, had the calc never appear to turn on.

Edited: 4 May 2011, 4:19 p.m.

[Thomas Okken]

Since Frido was saying that pressing any key appeared to turn the calculator on, that makes me think that the calculator was never actually turned off. I don't think a malicious program can do that, though -- IIRC, it is not possible to override the behavior of the ON key. So, either his calculator is in a bad state, which should go away after a hard reset, or there is a hardware problem.

Regarding malicious use of flag 11 (i.e. the old LBL 00 SF 11 OFF GTO 00 joke): you can override flag eleven by holding down R/S while turning the calculator on. Assuming it was really off, that is. :-)

- Thomas

[Geoff Quickfall]

Yes, I agree, a bad state. Was the calc actually off or is it always on and awakened by a key press.

"holding down R/S while turning the calculator on"

Thats the procedure used to stop the LO program from running.

It is the "OFF" function that is key assignable, not the "ON" function. And to confuse things, assigning OFF to R/S key, then running the LO program and trying to interrupt it with the R/S key causes the calc to turn off.

Yes, deviousness from fellow students, especially to the novice!

;-)

Didn't synthetics allow the on key to be assignable or maybe that was a PPC ROM or CCD ROM function?

Edited: 4 May 2011, 6:07 p.m.