HP 28c


Hello all,
I recall hearing something a while back about the hinged portion on these models, connecting both halves, being finicky or giving out in older models after long use.
Can anyone enlighten me about that? Also: any impresssions about use, quality?


I haven't seen any problems with the hinges on the calculators in my collection. The main problem is the battery door, which is easy to damage when changing the batteries. I've seen a few calculators with flakey displays. The keyboards seem to be pretty durable.


Agreed; the hinge seems as if it ought to be a likely failure with the clamshells, but I don't recall ever reading of it actually failing.

The battery cover is indeed difficult to to insert, particularly when in a rush to get it in place before memory is lost. Damage to the cover or the case in that area seems to be a common problem.



The only thing that I've known about that was bad about these units was that when I bought my first units in the late 80's, it kept losing memory if it was shaken a little, say when in a brief case. It was a few months old at the time and after getting frustrated I took it to a HP retailer who, after checking the serial number, replaced it with a new model. He told methat a bad batch were made with faulty battery contacts.
Apart from that, the unitis in pristine condition and I have no trouble with either battery cover or hinge. Nice unit. Won't part with this one foe anything




Other than the battery door, there are no major problems with the 28C/28S. One of my 28S accidentally hit the ground a couple times but nothing happened.

I had to put my 28Ss under storage for three years, with batteries. All of them had the clock program; when I took them out from storage it was still running and kept time more accurately than a wrist watch.

My two cents.


hello Juan J,
my son throw away the batteries in my HP28S,thankfull if you can help me what type of battery I need to replace the batteries..Thank you in advance..do have a nice day!!


Hello Martin,

The 28 uses three size N batteries. These are 1.5 Volts each. If I remember correctly, they are avaible from Eveready as model E90 and from Kodak as model KN. I prefer the latter, because it lasts longer and does not leak.

Be careful, as there are a few models with the same size (for garage door remote controls and similar devices) that are 3 Volts and even 6 Volts each. Check the voltage.

Hope this helps.


Randy reported broken plastic rivets to cause keyboard failures, not the hinge IIRC. Aside from this potential problem and the battery door, the clamshell models seem to be quite reliable. I have and enjoy an 18C since years and lately got a 19B.


Thansk everyone for the remarks and comments, it was valuable info for this HP collector!

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