older calculators not in regular use - how often and how long to run them

[vaklaff]

Hello

Sorry for raising a possibly trivial topic but my search-fu has failed me once again.

As some or possibly many people around here I have more calculators than I regularly use. Once or twice a years I take the stored ones out, plug batteries in and check if they still run. Recently I ran into a topic of capacitors in older electronics, with a suggestion to power them regularly so they don't dry up. My take from it was that my regular exercise is possibly not good enough. Not having any background in physics or EE, I've tried to dig up more specific advice, focused on calculators. This is what I have:

Quote:Electrolytic caps (and some tantalums) are another weak point. This is because the dielectric layer is formed from the electrolyte in the cap and breaks down if the cap is left discharged for long periods of time (years). Powering on every 4 months should be fine. However, if you do come accross one that has been left unpowered for a very long time, do not just power it up as the current through the cap can permanently damage it. Connect a 1k ohm resistor in series with the normal supply voltage for 24 hours for the capacitor to re-form. In old calculators I replace the electrolytic caps as standard (particularly prevalent in those with VFD and Panaplex displays).

by Bart (UK) at https://www.hpmuseum.org/cgi-sys/cgiwrap...ead=212077

and this thread by Alevin, ending in the same question I'd like to ask:

Quote:Any suggestion of periodicity (once a month? Once a year?...) and switch on time (minutes, hours,…)?

Also, is there a generation of calculators which starts the post-electrolytic (post-tantalum?) age, i.e. not needing this care? The Voyagers, perhaps?

Thanks in advance

[Rafa]

Not trivial at all. I also would be interested in a specific maintenance regiment.
I have three calculators and i've tried to make a habit of rotating usage, but invariably only one gets the regular daily use (school) while the other two are relatively a recent possession and i'm slowly familiarising myself with them so they get less than a couople of hours a week.
i could however anticipate that even though i equally like using them all, only one of them will be the daily driver while the others might at one point take the back seat.

So i would very much love to know how often should they be switched on, for how long, and if we say once every 3 months for an x amount of time, should then the batteries be taken out in between these uses?

cheers.

[brouhaha]

(06-27-2024 04:34 PM)Rafa Wrote:  Not trivial at all. I also would be interested in a specific maintenance regiment.

TL;DR: I suggest powering up most electronic devices for a minimum of a week per year to keep electrolytic capacitors from having excessive oxide degradation.

The only components for which any on-time is required are rechargeable batteries, which have been discussed to death elsewhere (TL;DR: don't leave ANY batteries in an electronic device for a long time, rechargeable or otherwise), electrolytic capacitors, and ceramic capacitors.

The issue for electrolytic capacitorrs is that when they are manufactured, they go through a "forming" process, which gradually (by means of current limiting) allows a DC voltage across the capacitor to ramp up to 125% to 150% of the rated voltage. This builds up an oxide layer on one electrode, with thickness proportional to the votlage, which is necessary for the capacitor to work. When an electrolytic capacitor is not used for a long time, that oxide layer gradually breaks down. If allowed to break down to below a minimum level for the in-circuit working voltage, then the next time it is used, there will be "punch-through" due to the working voltage being too much for the reduced oxide thickness, and the capacitor is destroyed and will have to be replaced.

In HP calculators, the electrolytic capacitors are in the power supply circuitry. In general I would suggest that having them powered on for a week per year would probably be sufficient to prevent oxide degradation from becoming a problem. That week could be distributed throughout the year in lesser increments, or it could be all in the last week of December.

It is possible to "reform" electrolytic capacitors that have suffered oxide degradation using essentially the same forming process that was used at the factory. This can only be done if the capacitor has not suffered punch-through, leakage, or any physical damage other than the gradual oxide breakdown. There are some people that make wild claims about reforming capacitors being bad, but some of the capacitor manufacturers actually recommend it for capacitors stored for long times unpowered, and there is even a US Department of Defense standard for capacitor reformation.

The other major problem with electrolytic capacitors is seal leakage, allowing the electrolyte to either physically leak out, or dry out in place. This can happen due to use of the capacitor beyond its ratings, at its ratings for a long time at high temperature and/or high ripple current, or manufacturing error (e.g., the "capacitor plague"). There's no fix for this other than to replace the capacitors.

Ceramic capacitors also have some long-term failure modes, but they are much slower, and there's not really any preventative measure to take.

Of course, all of the components have failure modes over the long term, but the batteries and capacitors are both the fastest to become problematic, and the easiest to take preventative or corrective measures. Generally all electronic components have a design life of five years, regardless of claimed MTBF of of claimed years of data retention of memory chips. The failure rate of components goes through a bathtub curve, where there is a high failure rate during or just after manufacturing (infant mortality), a period of very low failure rate, and then due to aging, a return to high failure rate (the far end of the bathtub curve). Components having a five year design life means that the manufacturer expects that the far end of the bathtup curve is somewhere beyond five years from manufacturing, but that they do not make any legal assurances that the components will operate correctly beyond five years. Obviously all HP calculators made prior to 2019 are mode of components that are already beyond their design life.

The reason that some things have an MTBF rating of hundreds of thousands of hours is that MTBF is a statistical measure (or predicition) of the failure rate of a POPULATION of items, not of any individual item. A 250,000 hour MTBF doesn't mean that there is any expectation that ANY units of the product will work that long. It means that if you operate 1000 units for 1000 hours each, on average you expect four units to fail within that time. The MTBF is only applicable during the design life of the unit, so if the design life is five years, the MTBF might help you understand how reliable you can expect the unit to be within those five years, but it literally tells you NOTHING about the reliability of the unit beyond its design life.

With regard to EPROM/EEPROM/Flash memory that has claims of data retention of 10, 20, or even 100 years, that too is a prediction based on the measured rate of charge leakage, which is an exponential decay function, and which is HIGHLY sensitive to temperature (higher temperature = shorter data retentioin). If you were to call any of the manufacturers and ask them if they warrant that the chip will hold data for the claimed retention time specification, the answer is absolutely not.

[vaklaff]

Thank you Eric for your detailed answer, much appreciated!

[bxparks]

Great information, thank you. The only minor quibble I might make is on this:

(06-28-2024 09:44 AM)brouhaha Wrote:  TL;DR: don't leave ANY batteries in an electronic device for a long time, rechargeable or otherwise

In theory, you are correct. In practice, my personal experience suggests that it is quite safe to leave in good quality NiMH batteries. My spreadsheet tells me that I am currently using 80xAA and 133xAAA rechargeable NiMH. Some of them going back to 2012. I have not seen a single NiMH battery leak during that time.

The LSD (low-self discharge) NiMH batteries are rated to keep their charge for years. The Eneloop batteries in particular are supposed to hold 70% of their charge after 10 years. The Amazon Basics batteries claim to hold 80% of their charge after 2 years. Not quite as good as Eneloops, but the Amazon batteries are about 1/3 of the price of the Eneloops, so I buy mostly Amazon batteries now.

For me, the convenience of keeping batteries in my calculators and having them instantly available outweighs the small possibility of a leak (which I have never personally seen among the 200+ NiMH batteries that I have).

But I agree with the advice for alkalines. Never keep alkaline batteries loaded in devices. And never use Duracell batteries. They leak more than any other brand that I have used. Fortunately I have switched almost all my batteries to NiMH. The only devices which won't work with NiMH are smoke detectors and carbon monoxide detectors.

[mfleming]

(06-28-2024 03:58 PM)bxparks Wrote:  In theory, you are correct. In practice, my personal experience suggests that it is quite safe to leave in good quality NiMH batteries. My spreadsheet tells me that I am currently using 80xAA and 133xAAA rechargeable NiMH. Some of them going back to 2012. I have not seen a single NiMH battery leak during that time.

I'll see your quibble and raise you a quibble

As I raised in an earlier post, there's more to consider than just leakage from NiMH batteries (I've never seen one leak myself). When under light load, the cells can not only discharge, left long enough under load a NiMH cell can reverse polarity. That according to another member cannot be recovered from. I have indeed tossed several cells that suffered that condition. Under some circumstances older calculators may be affected by fully depleted NiMH cells.

My cherished HP48GX no longer works because I didn't check it often enough, even though it was within arms reach.

Live and learn,
~Mark

[bxparks]

(06-28-2024 06:59 PM)mfleming Wrote:  

(06-28-2024 03:58 PM)bxparks Wrote:  In theory, you are correct. In practice, my personal experience suggests that it is quite safe to leave in good quality NiMH batteries. My spreadsheet tells me that I am currently using 80xAA and 133xAAA rechargeable NiMH. Some of them going back to 2012. I have not seen a single NiMH battery leak during that time.

I'll see your quibble and raise you a quibble

As I raised in an earlier post, there's more to consider than just leakage from NiMH batteries (I've never seen one leak myself). When under light load, the cells can not only discharge, left long enough under load a NiMH cell can reverse polarity. That according to another member cannot be recovered from. I have indeed tossed several cells that suffered that condition. Under some circumstances older calculators may be affected by fully depleted NiMH cells.

My cherished HP48GX no longer works because I didn't check it often enough, even though it was within arms reach.

Yeah, I've seen that reverse voltage happen on a very depleted battery. But I've only seen a single member of a set of 3 or 4 in series do that. My assumption was that the total voltage for the entire set of batteries always remains positive, even with the dead battery. But maybe if all the batteries go dead, the total voltage turns slightly negative because of the negative voltage of the first battery that went dead? I've never let the entire set of batteries go dead, so I can't say. I'm sorry to hear about those dead HP-48 calculators.

Also, I have always been able to recover a reverse-voltage battery. In the extreme case, it requires placing a good battery in *parallel* to the dead battery, and briefly shorting out the two, basically forcing a high *charging* current through the dead battery. It then gains enough positive voltage to activate the charger (which won't charge a 0V or -negative V battery).

[brouhaha]

(06-28-2024 03:58 PM)bxparks Wrote:  In practice, my personal experience suggests that it is quite safe to leave in good quality NiMH batteries. My spreadsheet tells me that I am currently using 80xAA and 133xAAA rechargeable NiMH. Some of them going back to 2012. I have not seen a single NiMH battery leak during that time.

The LSD (low-self discharge) NiMH batteries are rated to keep their charge for years. The Eneloop batteries in particular are supposed to hold 70% of their charge after 10 years. The Amazon Basics batteries claim to hold 80% of their charge after 2 years. Not quite as good as Eneloops, but the Amazon batteries are about 1/3 of the price of the Eneloops, so I buy mostly Amazon batteries now.

I mostly agree with regard to NiMH LSD, especially Eneloop. However, in general I still recommend leaving them out. Even Eneloop will probably leak _eventually_, though it will take much longer than for normal batteries.

[EdS2]

Wow, a week a year sounds like a lot, if something wasn't already in regular use. Do you mean about 40 hours a year, or 168 hours? Or perhaps only 7 hours as typical actual use?

[John Garza (3665)]

It can become almost a ritual. I turn on everything one weekend a quarter. That includes the calculators as well as the vintage computers and do some basic testing. If any abnormalities show up, repairs are scheduled for the following months. I also update the documentation on basic operations as needed. This is not to replace the user manuals - it just allows a casual user to perform some basic tests to verify operation. It's my checklist I use that weekend to help keep things organized.

-J

[brouhaha]

(06-29-2024 08:18 AM)EdS2 Wrote:  Wow, a week a year sounds like a lot, if something wasn't already in regular use. Do you mean about 40 hours a year, or 168 hours? Or perhaps only 7 hours as typical actual use?

I meant 168 hours

The oxide breakdown of electrolytic capacitors is a slow process, but regrowth of the oxide when normal operating voltage is applied is also a slow process. I believe 2% power-up time is conservative, and that a lower percentage might be adequate.

Note that some calculators, such as the HP Voyager series, do not use a DV-DC converter, and the aluminum electrolytic capacitors are powered whenever battery voltage is present. These do not need to be in the "on" state for capacitor maintenance, but the batteries should be reasonably fresh (e.g., silver oxide cells in first 70% of life), so that the voltage is not low

Note that the HP-41C family DOES use a DC-DC converter, so it actually needs to be in the "on" state to keep capacitor oxide formed.

Modern calculators with high-performance ARM processors and DRAM usually have DC-DC converters, because DRAM requires tightly regulated voltage. I haven't specifically looked at e.g. the HP Prime.

All PMOS and NMOS calculators use DC-DC converters, as they generally need to derive three different power supply voltages from the battery voltage.

[Garth Wilson]

The TI-59 had a voltage converter, and without looking back at documentation, I think it was just using an LM324 op amp for an oscillator, followed by charge-pump circuitry using diodes and capacitors.  It was a power hog, and one charge of the NiCd batteries was only good for two or three hours.  (They claimed four, but I never got anywhere near that, even when it was new.)  I never experimented to find out how much was from the LED display; but I used to just press the . key if I was putting the calc down for a few minutes, so the decimal point was the only LED lit, to reduce power consumption.  When possible, I'd always operate it with the wall-wart plugged in.

I'm surprised the 41 would have any kind of DC-DC converter in it.  CMOS circuits can work on a wide voltage range, and even in NMOS (which was a power hog compared to CMOS), the 1975  6502 was a 5V-only microprocessor.  (All the ones being made today are CMOS (65c02), and the data sheet specifies performance from 5V down to 1.8V.)

As for capacitors:  Replacing the electrolytics in old equipment is rather standard; but I don't think they go south as much as people think they do.  I worked at TEAC in the early 1980's, and fixed over a thousand tape machines while I was there, and I never found a bad capacitor except the big power-supply capacitors where they cheaped out and put in too low a WVDC for the application.  The ones in the audio circuits were always smaller, like 1µF or 10µF, which were usually more like 35V or 50V WVDC, in 12V circuits, and those never failed.  Granted, these were not 40+ years old; but the open-reel machines (not cassettes) were often 20+ years old.  I do have a portable open-reel tape recorder, one of the cheap ones from the early 1960's that showed up under lots of different names and in quite a few TV shows like Get Smart, which is about 60 years old, with the original capacitors, and it still works fine.  I got it cheap on eBay for the historical value.

[BobVA]

Besides the electronics, don't forget the mechanics which are particularly sensitive to "closet rot". I operate my three printing calculators (two 97's and a 19C) weekly, to keep the feed rollers, etc, from flat-spotting, and I run a card through the 67/97's a few times a year for the same reason.

[bxparks]

(06-29-2024 07:29 PM)brouhaha Wrote:  I meant 168 hours

Yeah, that's never going to happen for me. Most of my calculators have a ~10 minute automatic power off. I'm not going to sit front of a calculator and hit the ON button 1000 times. Multiply by the ~20 calculators that I own. Nope, I'd rather lose the occasional calculator than waste my life doing that.

What I do is check my rarely used calculators about every 3-6 months. I make sure that the NiMH or the CR2032 batteries are still good. I recharge the NiMH or replace the CR2032 if needed. That's it.

[Massimo Gnerucci]

(06-29-2024 10:58 PM)bxparks Wrote:  Yeah, that's never going to happen for me. Most of my calculators have a ~10 minute automatic power off. I'm not going to sit front of a calculator and hit the ON button 1000 times. Multiply by the ~20 calculators that I own. Nope, I'd rather lose the occasional calculator than waste my life doing that.

Just disable the auto shut-off.
Or automate the process... :D

[Maximilian Hohmann]

Hello!

(06-29-2024 10:58 PM)bxparks Wrote:  ... Multiply by the ~20 calculators that I own. Nope, I'd rather lose the occasional calculator than waste my life doing that.

Same here. I have more than 1000 calculators. The electricity bill is going to kill me if I run them each for four weekends every year...

Another thing to consider is that not every failure of old electronics is caused by capacitors. Degrading solder joints, degradation of bonding wires and sealing of chip housings and general degradation of semiconductor materials - just to name a few. Many of these are accelerated by higher temperatures, so running old electronics for longer periods may preserve the capacitors but cause other components to fail.

So far I have had very few cases of calculators that I stowed away in working order and pulled them out again after several years to find them in non-working state. With the exception of a few with forgotten batteries inside...

Regards
Max

[bxparks]

(06-30-2024 12:45 PM)Maximilian Hohmann Wrote:  Same here. I have more than 1000 calculators.

Wow. I'm trying to imagine what 1000 calculators look like. If we arrange them in a 20 high x 50 wide grid, with each calculator in a 20cm by 10cm cell. That's 4m high x 5m wide (more commonly known as 1/267.56 of an American football field :-P) You'd need a ladder to take a photo of that.

[Maximilian Hohmann]

Hello!

(06-30-2024 03:56 PM)bxparks Wrote:  Wow. I'm trying to imagine what 1000 calculators look like. If we arrange them in a 20 high x 50 wide grid, with each calculator in a 20cm by 10cm cell. That's 4m high x 5m wide (more commonly known as 1/267.56 of an American football field :-P) You'd need a ladder to take a photo of that.

Yes, if you lay them flat on the floor. But mine are in boxes stacked on top of each other... If every calculator uses 20cm * 10cm * 5cm of space, in total 1000 calculators only occupy one cubic meter. Mind you, there are people on this forum who don't just collect calculators (like myself), but also the original boxes they came in, manuals, accessories, etc. For that you need a dedicated room in your house or an extra appartment.

Regards
Max

[AndiGer]

How does Thomas Kirchhof here in Germany write (translated to my words) on his website?
„I am happy I collect calculators and no tractors“ :-D :-D

[Rafa]

hmmm. I would rather not have to adopt meticulous regiments with spreadsheet and schedules, but i also would be a bit itchy leaving things to chance.

I resolved to rotating the 20s and the 35s at school for about 2 hours daily plus an hour of homework. so i guess that's sufficient of fixed regular use each week for each of the two calculators. I try to use the 28s daily for about 30 minutes of messing around.
A 27s is however making its way slowly across the atlantic and will be replacing the 20s.

I feel like i would rather sell the 20s and the 35s than maintaining this routine of rotation. But if turning these two on once a week for some minutes and not having to take out the batteries in between then i would happily keep them.

Can someone confirm whether or not this would be sufficient to keep the 20s and 35s in good health?