HP 28S: How to Resuscitate?


I have a 28S that is holding on to dear life. It needs some help to bring it back to health. Here's the problem: When the batteries are installed, and the ON button is pressed, ALL the pixels come on (and stay on), but nothing else happens. It won't respond to any keypresses (other than the initial ON key press).

I've tried a cold start Reset <ON + INS + RightArrow> (28S equivalent of 48 <ON + A + F>). I've tried a warm start <ON + UpArrow> (28S equivalent to 48 <ON + C>. It won't even turn off unless I remove the batteries.

I've shorted the battery terminals with a paper clip (for about 60 seconds), and even temporarily reversed the N-cell batteries. There is no external Reset hole to press.

Any thoughts or ideas to try? BTW, the batteries work great in another 18C and 19B I have.

Any and all suggestions welcome. Thanks.



Sadly, it's time to kiss it goodbye. The symptom is indicative of one of the chips going bad.


I kind of came to the same conclusion. Good thing I only spent $5 on it, including the Owner's and Reference manuals.

Thanks Eric,



Well, at least you got a good deal on the manuals. Now you can buy another one that doesn't come with manuals.

I'd love to get a broken 28S to take apart for high-resolution photos. But perhaps you should wait and see if anyone else has advice on other things to try to attempt to revive it. I can't think of anything, but who knows.


I've had Pioneers that acted similar, and it was a "stuck" key (actually, a dirty keyboard sandwich) that was the culprit.

Only problem is, how to test? Taking one of those apart seems to be impossible without in the process destroying the plastic posts that hold it together.

I've got one "in a bag". I've often thought that with my drill press and about a hundred small stainless steel machine screws and matching acorn nuts I could drill out most of the posts (right through to the outside), screw the thing together, and have a "studded" 28s.

But like most of my ideas -- all thought and not much action!

Possibly Related Threads...
Thread Author Replies Views Last Post
  Riemann's Zeta Function update (HP-28S, HP-48G/GX/G+, HP-49G/G+/50g) Gerson W. Barbosa 0 515 06-30-2013, 01:01 AM
Last Post: Gerson W. Barbosa
  Riemann's Zeta Function (HP-28S) Gerson W. Barbosa 8 1,200 02-03-2013, 03:23 PM
Last Post: Gerson W. Barbosa
  28S Pi Functionality Matt Fegenbush 3 752 10-17-2012, 02:15 AM
Last Post: Nick_S
  HP-28S plays "Happy Birthday" Kevin F 0 477 08-06-2012, 04:53 PM
Last Post: Kevin F
  HP-28S Mathematical Applications manual errata Tom Sauntry 2 646 07-25-2012, 09:54 AM
Last Post: Tom Sauntry
  HP-28S Syntax Errors William N Strew 7 1,173 07-15-2012, 05:09 PM
Last Post: Luiz C. Vieira (Brazil)
  50G<-->28S SYSEVAL map Matt Agajanian 3 777 05-29-2012, 03:28 PM
Last Post: Christoph Giesselink
  HP-28S Battery Cover Kerem Kapkin (Silicon Valley, CA) 2 831 04-09-2012, 10:29 PM
Last Post: aj04062
  A cure for 28S death Ed Bacon 11 1,325 04-02-2012, 09:04 AM
Last Post: Olivier De Smet
  Re: OT: 28S prices Bart (UK) 5 902 02-29-2012, 02:42 AM
Last Post: Nick_S

Forum Jump: