No luck with HP25s



#20

It seems the woodstock series are much less reliable than the classics. Or is it just that I like the HP25 better, and therefore use it a lot more than the other calculators?

Anyway, this is the third time an HP25 has died on me. I can still enter numbers and even store and recal them. But as soon as I execute any operation, I get 0.000000000 in the display.
Any idea what could cause this? I am guessing it is the ACT. Any other suggestions?

Cheers,
Harald

PS: luckily my HP25c is still working like a charm *knock on wood*


#21

Woodstock series units are very reliable if you throw away the original HP charger and always charge batteries externally to the calculator. I've gone to the extreme measure of disconnecting the charger diode in my 25 so it can never be damaged by over-voltage.

In the 25, ACT failures are common as well as rom failures. That behavior sounds like the ACT. Any ACT from the series should work with the exception of the 21 (no I/O pin) and the 27 (nmos, not pmos).


#22

Quote:
Woodstock series units are very reliable if you throw away the original HP charger and always charge batteries externally to the calculator. I've gone to the extreme measure of disconnecting the charger diode in my 25 so it can never be damaged by over-voltage.

I am aware of the problem. The first unit that failed, I had modified to run off the charger without the battery. I am certain though that it did not see any overvoltages due to that. It failed after 5 years of more or less continous running, as it was always on my desk and I never turned it off.

The other two unit I ran on batteries only. Well, most of the time. Certainly the last one failed when running of batteries. I used it one day and it worked fine, picked it up the next day and it was faulty.

#23

I have several Woodstocks and they've been refurbished with Tenergy cells. So, in that case, with these new batteries, how should these be charged up? What options do I have if I do not have the external battery charging bay (sorry, I can't recall the part number)? Can I take a spare Woodstock like a 21 and then just swap out the battery pack from a 25C or 29C and recharge the pack from a 21 since it has no continuous memory chip to damage?

Thanks

Edited: 20 July 2012, 12:27 p.m.


#24

Yes, charging in a non -C model that is turned off at the time is a good idea.


#25

Thanks! By the way--just so I can get the gist of this, given new technologies with old hardware, just what causes the overload? For example, is it because I'm using the combination of a 25C or 29C plus the original Woodstock charger with the new Tenergy 650mAh or 1000mAh batteries? Or is it just the way it's always been such that charging C models of Woodstock units was problematic from day one? And what makes non-C Woodstocks much safer to charge with the new batteries and original HP charger?

Thanks again

Matt


#26

It was an issue from day one. In contrast to the classic series, the woodstocks are not supplied with a regulated voltage from the charger. The battery is needed to limit the voltage to a safe level. If the connection to the battery is bad, the voltage can be too high. For the non c models this is not a problem, as long as they are not turned on. With the c models turning off the calculator does not help, as the continuous memory is supplied even with the switch in the off position.


#27

Okay. Now I know for the better. Good thing I found out about this early and it's even better that I have a non-C, 25 and 21 that I can use as charging bays. Thanks for the "heads up."

Edited: 20 July 2012, 6:34 p.m.

#28

Hi.

I have one with the same problem, and Randy's mentioning of a defective/failing ROM applies.

Cheers.

Luiz (Brazil)


#29

Ok, in that case I will try my luck with a rom from one of the failed units. I am hoping it is the RAM that failed on that one.
Do you know which one of the ROMs is likely to be the faulty one? The ROM/anode driver? Or the other one?

Cheers,
Harald


#30

Hi, Harald.

IIRC, the ROM/anode driver has the basic, elementary set of functions that might be common to all (mostly) units, like stack/register manipulation and basic arithmetic/scientific computing, as we find in the HP21. The complementary ROM, the one closer to the ACT, probably adds programming handling and extra stack/register manipulation.

But this is some brain work of mine, though. Anyway, there is a homepage I could not find the address where all known IC's with their ID's, function and calculator they are found are listed. I copied the page for future consulting, but it is not in this computer, though. Surely a better description of the ROM's contents will be found there.

Success!

Luiz (Brazil)

Edited: 20 July 2012, 10:52 a.m.


#31

http://www.brouhaha.com/~eric/hpcalc/chips/

possibly?


#32

Yep, that's it!

I'll save a copy of the address in a safer place, this time.

Thanks!

Luiz (Brazil)

#33

It was the ROM! It is working again. Luckily the other calculator seems to have another fault. That one occasionally displays (or should I say displayed) "error" when typing things.

Thanks to everyone!


#34

Hi!

Thank you for sharing the success with us!

Cheers.

Luiz (Brazil)

#35

A terrific resource for this is:

http://www.jacques-laporte.org/Woodstock/ws_HW_main.htm

#36

What is going on here?
http://www.ebay.de/itm/110915824386?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648


#37

I've no words.......but the winner has a lot of money!!

Edited: 21 July 2012, 9:50 a.m.

#38

Quote:
It seems the woodstock series are much less reliable than the classics. Or is it just that I like the HP25 better, and therefore use it a lot more than the other calculators?

Hi Harald, I missed this your post, sorry...... but I'm happy for your success.......you see, it's true that too much love (for the HP25, I mean)sometimes kills!


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