HP 41CX Auto-Off behavior

[polbit]

Acquired another CX (because why not!) and visually it is in fantastic condition. However I noticed one thing - it turns off after 6 minutes of inactivity instead of the usual 10. From my reading I understand that this is not adjustable and a capacitor is responsible for the time. Does that mean that I can expect it to get worse? Is it something that I should replace, will it cause any other issues?

[rprosperi]

Is it possible this is a double-speed CX? Using [XEQ] "BEEP" is the simplest way to check.

[polbit]

(11-23-2023 06:26 PM)rprosperi Wrote:  Is it possible this is a double-speed CX? Using [XEQ] "BEEP" is the simplest way to check.

No, it sounds normal, and feels as fast as my other 41s

[Monte Dalrymple]

(11-23-2023 06:26 PM)rprosperi Wrote:  Is it possible this is a double-speed CX? Using [XEQ] "BEEP" is the simplest way to check.

The auto-off time is controlled by a small capacitor on the CPU board, but the oscillator itself is on the display driver chip on the main board. The capacitor controls the frequency of a dedicated oscillator; circuitry counts the pulses and deactivates the DPWO line when the count limit is reached. This function is independent of the CPU frequency.

[rprosperi]

(11-23-2023 08:43 PM)Monte Dalrymple Wrote:  

(11-23-2023 06:26 PM)rprosperi Wrote:  Is it possible this is a double-speed CX? Using [XEQ] "BEEP" is the simplest way to check.

The auto-off time is controlled by a small capacitor on the CPU board, but the oscillator itself is on the display driver chip on the main board. The capacitor controls the frequency of a dedicated oscillator; circuitry counts the pulses and deactivates the DPWO line when the count limit is reached. This function is independent of the CPU frequency.

Thanks Monte, I've wondered about this. Since the BEEP commands sound super-fast, I wondered if the shut-down timer did as well, since that feature predated the time/clock features of the TIME module and subsequent CX. Thanks for clarifying this.

[do2]

(11-23-2023 05:44 PM)polbit Wrote:  Acquired another CX (because why not!) and visually it is in fantastic condition. However I noticed one thing - it turns off after 6 minutes of inactivity instead of the usual 10.
[snip]

I've just tested this feature on my 41c and 41cx Halfnut and - lo and behold - the older 41c switched itself off after 10 minutes, while the 41cx had been gone dark after around half of the time already. Could this be a common behaviour with the newer architecture?

Just for full disclosure: My 41c was powered from Alkalines and the 41cx from NiMH-cells, although I don't think that this should be relevant for the auto shut-off time.

[rprosperi]

One of my FullNnut CX took ~11 minutes.

I'll try a HalfNut CX and update these results.

[born2laser]

All this made me curious, I just checked. My fullnut CV takes roughly 9 and a half minutes to turn itself off

Juan

[polbit]

The CX that shuts off in 6 minutes is indeed a half-nut, my other two CXes are full-nuts. The plot thickens...

[Sylvain Cote]

I did the test with seven of my 41's and here are the results ...

Code:

2101A05170  8m20s 41C  Fullnut
2240S41176  7m50s 41CV Fullnut Blanknut
2407S40051 10m32s 41CV Fullnut
2552S20514  7m08s 41CV Halfnut
2814S20780  6m08s 41CX Halfnut
2814S20800  6m01s 41CX Halfnut
----------  9m20s 41CL Fullnut v5

[do2]

Following the lead of Sylvain, I checked the auto-off timings of my 2 HP-41's in a more scientific way. Please note that I clocked the timings per hand, so the accuracy should be around +/-1s.

And I took a series of 3 measurements in a row, with the first one immediately after a cold start:

HP-41c from 1982: 9:28/9:29/9:30
HP-41cx, Halfnut from 1987: 6:15/6:27/6:28

After a couple of days, I clocked the following timings for the Halfnut (first one again with a cold start):

HP-41cx, Halfnut from 1987: 6:23/6:24/6:25

From these results and without knowing the schematics, one would have suspected an electrolytic cap in play here. Nothing new for those who already know. But it's a little bit like unlocking a small secret in a game, even if it's not necessary for the main campaign...

[polbit]

I think it's safe to say that halfnuts have a time-out set around 6 minutes whereas the fullnuts are closer to 10 minutes or so. Same pattern was followed by my 41C and halfnut CV.