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HP 35s battery drain
07-25-2020, 02:06 AM
Post: #1
HP 35s battery drain
I bought a HP 35s a while ago at a local store. However, the first time I used it with the original batteries it lasted about 3 weeks. Then when I bought others that were good they lasted me 15 days, and now when I buy other batteries they only last me like 4 days. Are there any defective batches of these calculators or why is it downloading so fast? I have seen that on ebay they sell some rechargeable CR2032, could they help me not to have to be buying and spending so much money to change them so often?
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07-25-2020, 06:24 AM
Post: #2
RE: HP 35s battery drain
I don't know what batteries you're using but cheap Chinese no-name lithium batteries are going to have much less life in them and perform nowhere near as well as batteries of a reputable brand.

This said, that the first set of batteries only lasted 3 weeks should have been a good indication that there was something wrong with the calculator. It is very likely that one of the decoupling capacitors inside it is leaking.

If your calculator is still under warranty then take it back. It is faulty. If not then you're probably better off getting another one.

There are only 10 types of people in this world. Those who understand binary and those who don't.
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07-25-2020, 08:26 AM (This post was last modified: 07-25-2020 08:27 AM by Maximilian Hohmann.)
Post: #3
RE: HP 35s battery drain
Hello!

(07-25-2020 02:06 AM)math7 Wrote:  Are there any defective batches of these calculators or why is it downloading so fast?

The HP-35s has always had a problem with battery drain. There are several threads about this topic on this forum. If I remember correctly Katie Wessman has solved it by replacing a potentially leaking capacitor. However this "rapid" battery drain has always been a matter of months (I have one HP-35s that lasts about two months, another which lasts for half a year) and not days. Yours must clearly be defective!

Regards
Max
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07-25-2020, 06:24 PM
Post: #4
RE: HP 35s battery drain
Probably "Katie Wasserman" not Wessman.
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07-25-2020, 09:30 PM
Post: #5
RE: HP 35s battery drain
(07-25-2020 06:24 AM)grsbanks Wrote:  I don't know what batteries you're using but cheap Chinese no-name lithium batteries are going to have much less life in them and perform nowhere near as well as batteries of a reputable brand.

This said, that the first set of batteries only lasted 3 weeks should have been a good indication that there was something wrong with the calculator. It is very likely that one of the decoupling capacitors inside it is leaking.

If your calculator is still under warranty then take it back. It is faulty. If not then you're probably better off getting another one.

The batteries that I have put in are a good brand ... from a brand that starts with m and ends with it, and from another brand that starts with S and ends with Y so as not to advertise, haha. Yes it must be defective, but the warranty passed more than 1 year ago, because I did not use it as much and sometimes had it stored.
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07-25-2020, 09:31 PM
Post: #6
RE: HP 35s battery drain
(07-25-2020 08:26 AM)Maximilian Hohmann Wrote:  Hello!

(07-25-2020 02:06 AM)math7 Wrote:  Are there any defective batches of these calculators or why is it downloading so fast?

The HP-35s has always had a problem with battery drain. There are several threads about this topic on this forum. If I remember correctly Katie Wessman has solved it by replacing a potentially leaking capacitor. However this "rapid" battery drain has always been a matter of months (I have one HP-35s that lasts about two months, another which lasts for half a year) and not days. Yours must clearly be defective!

Regards
Max


I'm going to look to see if I find that thread you say, and learn first how to open the HP 35s without damaging it, and then how to replace that capacitor. I have a soldering station and some things, but it is scary to damage it.
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07-26-2020, 10:09 AM
Post: #7
RE: HP 35s battery drain
(07-25-2020 06:24 PM)Gene Wrote:  Probably "Katie Wasserman" not Wessman.

Yes, of course. Sorry Katie...
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07-28-2020, 11:35 AM
Post: #8
RE: HP 35s battery drain
(07-25-2020 08:26 AM)Maximilian Hohmann Wrote:  ...solved it by replacing a potentially leaking capacitor...

Could you drop a link here?!

Thanks,
Csaba
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07-29-2020, 02:24 PM (This post was last modified: 07-29-2020 02:33 PM by jebem.)
Post: #9
RE: HP 35s battery drain
This is a issue reported by several owners along the years on different internet forums.
Apparently there is no solution documented to fix it, except to ditch it and buy a new one.

It seems that the battery life is around 8 months when using it 1 hour per day, as seen on several seller's publications still easy to find by using Google search engine.

By searching this forum for this issue it is possible to find one comment by Katie Wasserman where she reports that a fresh set of batteries should last for around two and half years when leaving the calculator powered off.
This relatively short battery lifetime would be caused by a somewhat high standby current of 10 microampere, related to the power supply design and chip technology, and software routines used for deep sleep management.

I couldn't find any reports on failing capacitors causing this issue on this model.
However, surely a defective capacitor may cause excessive current consumption, and this model uses 3 electrolytic capacitors that are easy to replace.
Try using long life 105°C electrolytic caps from a new stock.
Old caps, even new in the box, can show signs of current leakage among other defects.

Measuring the current consumption in these cases would help, and it just requires a good multimeter, a external 3V battery holder or power supply, a pair of cables with oligators.

Other than that, there are quite a few SMD caps, resistors, and transistors, besides the two chips and the crystal/resonator.
Having the time and skills, all these components (except the two chips) can be replaced, starting with the ones connected to the two batteries power cables (that is the power supply section).

Eliminating all the above suspects, then a defective gate inside one of the two chips is the most probable cause, and it means a dead end imho.

Edit:
Look to Wikipedia for HP 35S. A nice internal view picture shows some details.

Jose Mesquita
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