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New HP 28S, strange behaviour - Lithium - 03-21-2016 07:44 PM

Hi all!

Long time lurker, first time poster here!

I finally jumped ahead sadly because I just receive a nice (perfect physical condition, perfect battery door...) made in USA 28S, and if the self-test run fine and all basic calculations are ok, I can't access to any menu or advanced functions.

When I received it and tried to print something on my 82240A printer (the first thing I tried since the printer was laying on my desk and powered on, lol, just used it to print a grocery list with my 19B), it displayed the message "out of memory". I answered yes to all questions before trying to reset memory (I was curious of what previous owner could have programmed), but all I got was the continuous display of the appointment/busy calc.

Now when I try to do anything that is not on the numeric keybord, the calculators hangs and displays the busy sign. I can do the self-test ever and ever (ok 28S), reset memory, but no improvement. Also when it hangs the pile displays


(this is my first 28S, don't know if normal)

I can access catalog and units (mem argument when used through catalog returns 32K memory, and the few thing I tried through catalog seem to work ok), but anything else just displays the busy signal and I have to do a soft reset (on + C) to get it back to pseudo-normal.

Do you know what could be wrong with it? I opened various 18/19B in the past with various rate of success, but since I payed a nice sum for this "cosmetically perfect" 28S, I'd rather return it to seller if it is not usable...

I'll try to let is without batteries for a while, hoping for improvement Smile


RE: New HP 28S, strange behaviour - Jlouis - 03-21-2016 08:47 PM

Your HP28s looks normal,

the numbers you mention is the stack numbers.

Maybe you are used to algebraic calculator and does not know RPN.

HP 28s is a calculator with RPN entry logic.

Please refer to this page of this site to learn RPN:


Theres also a good youtube video that explain RPN very well:


Don't forget to read the calculator manual, where it explains how your calculator works.

If you don't have it, you can order a scanned pdf one here in this site.

After you did all of these, if you have others doubts, please ask here.

Hope I have helped


RE: New HP 28S, strange behaviour - Marcio - 03-21-2016 08:52 PM

To complement what JL said above, you may also want to check out this RPN tutorial.

RE: New HP 28S, strange behaviour - Lithium - 03-21-2016 09:08 PM

Thanks for answers, but I'm used to RPN/RPL Smile
I have several HP calculators, even if this one is my first 28S.

The stack normally displays


but when it hangs it shows


and nothing happens. Basic calculations are ok, but accessing to evolved functions of menus is impossible :/ Is there something to try before sending it back?

RE: New HP 28S, strange behaviour - rprosperi - 03-21-2016 11:49 PM

(03-21-2016 09:08 PM)Lithium Wrote:  Is there something to try before sending it back?

Remove the batteries and short the (end) terminals together with a short piece of wire, or scissors, etc. to dissipate any remaining charge. Let it sit overnight. The next day, insert known good or even new batteries, and reset the machine after power up. If it still misbehaves, I would ask for a refund. It could be fixable, but since you've paid for a fully working unit, and it clearly is not, you are justified to ask for a refund, or perhaps for a partial refund and keeping the unit (for repair), but most sellers (understandably) will not trust a buyer and agree; but it's worth asking.

RE: New HP 28S, strange behaviour - Lithium - 03-23-2016 06:08 AM

Unfortunately, after 36h without batteries, the calculators is still hanging when trying to access menus Sad

Back to the sender then... I'll try an exchange since he has another 28S made in USA!

Thanks all for answers.

RE: New HP 28S, strange behaviour - Lithium - 03-23-2016 08:00 PM

Well, so the pretty 28S has been returned.

To fight the frustration, I bought a non-functional 17BII for a few € (these one are much easier to open, and since it was cheap, I haven't much to loose!), and a promising 18C.
But still no 28...it looks to me this 28S is just the right model between the "basic" 18/19B and the 48S/G, with enough horsepower and functions, and also a nice display in a practical form factor with alpha keyboard.

Now I'm looking for a decent 28S !

Cheers from Brittany

PS: I have a "blind" 48G, I ordered some ram chips to upgrade it to 128K and experiment, but its IR receiver is dead, any idea of a suitable replacement part ?