My HP-27S would not shut off, help!


Just when I thought I've seen everything there is to my HP-27S calculator in the last 15+ years of ownership, a surprising new feature showed up yesterday. Everytime I turn the power off now, it automatically turns itself on after half a second (sometimes even 15 seconds).

This new auto-power-on feature, as I termed it, follows some bizarre beeping late last night. I was oblivious to the entire incidence as I was soundly asleep, but my wife alerted me in the morning that my calculator was beeping non-stop for hours. The beeping only stopped after I removed the batteries (the whole system froze like Windows). When I put the batteries back, the undesirable feature shows up. Thinking it might be a battery problem, I purchased and put in a new set of batteries to no avail.

I'm hoping there is something I could do to fix it. Much as I love my HP-27S, I hate to have to open the battery compartment and remove the batteries every time to turn it off. Any idea is appreciated (other than installing a power switch :), thanks in advance.


Check your appointment alarms. I believe the Hp27s has a clock calander feature with alarms just like the Hp17/19 business calculators.


Thanks, I checked again just to make sure and there is definitely no appt set.

Here's an update however. I left the batteries out overnight and put them back in this morning. I turned the calculator on , then off, it remained off for 20-30 seconds before it turned itself on again. I turned it off again and it took about 3 seconds before it turned itself on. After that, everytime I turned it off now, it comes back on in half a second. Other than this auto power-on, everything else works fine still.


Hi Davin,

Have you tried removing the batteries and then shorting out the battery contacts to discharge the internal capacitor? This should reset the calculator. Maybe it'll also reset some data bit that is causing your problem.

Does the 27S have any other resetting mechanism - such as a two or three key combination??

Good luck.



Yup, I tried shorting the battery terminals before but no luck. There are buttons to reset the machine. I tried those too w/o success.


Hi Davin,

I have looked in my manual for the 27s, and in addition to the removing batteries, then shorting the terminals for a few seconds, there are some other tests and procedures:


Hold down CLT wehile you press the third menu key from the left. It may be necessary to repeat the reset keystrokes severl times. The HP 27S displays "machine reset" to confirm. This reset will occurr automatically in some circumstances. (memory remains intact).

**Erasing Continuous Memory (delete4s everything you have stored):

Hold down CLR, and press the leftmost and rightmost menu keys simultaneously (all three keys at once). When the keys are released, you should see "MOMRY LOST"

***Self test:

1. Turn calc on. 2. If you have the printer, turn it on, too,
3. If possible, return to the MAIN display (shift main)
4. To start, hold down CLR while you pres the fifth menu key from the left (pressing the 4th menu key starts another meun test used at the factory. If you accidentally do thi one ytou can stop it by holding down the CLR key while you press the third menu key from the left).

Once the self test has begun, do not press any keys until you are ready to halt the test.

5. during the test, the calc beeps periodically, and displays various patterns and characters. Watch for one of two messages that are displayed at the end of each test cycle, before the test automatically repeats:

If it passes, "OK-27S-E"

If it displays FAIL followed by a 5 digit number, then you require service.

If you fail, run it again to be sure you did not cause it to fail by pressing the wrong keys etc.

Best regards,


Edited: 23 Feb 2005, 12:43 p.m.


Hi Bill,

Yup, I tried all those combinations of keys. All the tests went fine w/o error. I also reset the machine and cleared the memory. In addition, I also did the test where I've to press every single key from top to bottom and left to right to test the keyboard. All checked out okay.



Isn't the ON button lower than normal? If the button is defective, it may "press" itself on small vibrations due to a bad isolation on the contacts - but this is only a wild guess...

Best regards,



Hi Nelson,

Thanks for your reply but somehow I don't think that's the case because it only powers itself on after it was turned off via the keypad. It would not turn itself on if I were to take the batteries out and put them back in no matter how hard I shake it.



Clearly you have a special calculator. Start the eBay bidding at $500 and hope for the best. Congratulations.


That's an excellent idea. Instead of $500, I'll start at $9.99. Feel free to enter your bid at:



After you told this fancy story to all of us in this forum, you should offer this calculator worldwide. Let the geeks in other nations have a chance, too!

BTW: shipping outside the US is no witchcraft, even for US citizens ;-)


Fair enough. All geeks welcome.

Bid more and prosper.



I'm on your list :-))

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