Help with HP-42S


Help. My father just gave me a 1985 HP-42S calculator. The batteries were dead so I put in new 1.5 volt batteries and all it does is constantly beep which I think it is suppose to do when there is an error. Is there a way of resetting the calculator. I keep trying to put the new batteries in and it keep doing the same thing,... beeping. The only way to get it to stop is pull the batteries out. Thanks Steve in Seattle


Are you sure it is an HP-42S ?

Could there be a stuck key, which forces the beep?



Raymond I am positive its an HP-42S RPN Scientific calculator. I checked the buttons and they all seem to be depresssing and springing back out. Thanks for the response.


Try removing the batteries and briefly short circuit the battery terminals inside the calculator with a piece of wire.


... keeping the batteries in the compartment while briefly shorting the calculator's terminals. If this procedure is briefly executed, as John mentioned, the batteries will not be damaged and no more than 4.5 Volts will be applied to the batteries terminals. This way, the chances for an ESD (ElectroStatic Discharge) and consequent damage to the calculator are fairly reduced.

Just an additional information.

Luiz (Brazil)


Thanks John. You sure it won't hurt the calculator??


It shouldn't cause any problems.

I double-checked the HP-42S Owner's Handbook. Here is what it says:

Now turn the calculator back on. If it does not function, you might have taken too long to change the batteries or inadvertently turned the calculator on while the batteries were out. Remove the batteries again and lightly press a coin against both battery contacts in the calculator for a few seconds. Put the batteries back in and turn the calculator on. It should display Memory Clear.


Thanks a lot John I really appreciate the help. I will give it as try.


Hi, Steve;

some time ago, one of our contributors mentioned this sort of symptom, and in his case (was it Randy Sloyer?) it was necessary to resolder the RAM chip.

I cannot tell you for sure, but that's what came to my mind right now. This is sort of a "final solution", but may bring your 42S back to life. These pioneers (HP27S, 42S and 17B/BII) are quite fearless, and they generally survive to soldering.

Opening the case is another story, and many guys in here have the skills and experience to share, if you wanna try it.


Luiz (Brazil)


Thanks Luiz Trying to take it apart and soldering it is probably over my head. Is there someplace we could send it in for repairs?? I think I will try the battery terminal short curcuit first.


Hi, Steve;

I read here some guys mentioning a sort of "repair center", not an HP repair center, that offers service for some HP calculators. Both HP41 and HP42S are included.

The fact is that (sadly) HP no longer offers service for the HP42S. The only way is trying the "off-line" repair centers. I myself repaired some HP42S, and I also upgraded at least five units to 32KBytes RAM. That's why I remember reading about the continuous beep. BTW, to those interested on this sort of upgrading, I found compatible 32KRAM chips in some "ancient" HD boards. No, they are not MFM units, instead some 170MBytes to 480MBytes IDE units. I'm collecting the HD's and related chips ID's so I can further search for their characteristics.

I'm sure you'll find people closer to you that will help you in any way you need. Anyway, be sure that I'd help as well, but as I mentioned, my spare time is "none". I think I'll be ready to get my daily HP-related activities back after the mid December, while I'm resuming some HP-related activities in the course.

I'm just resting for a while as I'm writing a brief tutorial (in Portuguese) related to LaTeX instalation and use in a Linux environment. And it's already 3:50 AM in Brazil. I'm taking a nap and getting back to the keyboard in a few hours, if you don't mind.


Luiz (Brasil)



You might want to investigate

if none of the suggestions work.

I haven't sent any repairs to Fixthatcalc, so can't give a recommendation. Perhaps others who have used them can give feedback.

Hope you get it working -- the 42S is a great machine.



This behaviour - where the 42S beeps constantly - is exactly the same problem as I had when upgrading one of my 42S's to 32K RAM. The reason then was that one of the legs of the new RAM chip was not soldered sufficiently.

So, if nothing else helps, I would suggest attempting a 32K upgrade :-) (Probably, Randy Sloyer could help you with that if you feel uncomfortable opening up the calc yourself).

Best regards,
Erik Ehrling (Sweden)


I'm no expert, but I remember reading in the archives that when the HP-42S calculator goes into it's beeping mode, it can mean one of two things:

First: the calculator has a self protecting and anoying feature, as it sounds off automatically (beeping) warning you that my batteries are low and I need changing now! before I loose my continous memory and you loose your mind. Persistant little bastard thinks it's a smoke detector!!! Actually, when the calculator is off, it can detect a low-battery condition and an internal system flag is set which will make the calculator beep non-stop. So make sure you have some FRESH batteries handy, Silver Oxide batteries, i.e. Energizer's 357/303 also known as "357BP" or Duracell's D303/357B are best, or FRESH alkaline Duracell's PAX76A675AB also known as "76A" will do too. Also make sure the battery terminals are free of any corrosion or hand oils, handle the batteries by their edge, use a little alcohole and Q-Tip to clean the battery contacts and faces if you fingered them.

Any way: Resetting the Calculator is simple and it does not matter if the calculator is ON or OFF: Simply hold down the EXIT key while you press and release the SQUARE ROOT key once, then release the EXIT key. Repeat if necessary. That should stop the beeping and the display will show either "Machine Reset" in the top line's Y registry or in your case "Memory Clear", since it's been without power for a long time. Press the EXIT key to clear the display and your ready to go.

Also: If you unknowingly turned the calculator ON while the batteries were out, the calculator can misbehave. Remove the batteries and lightly press a coin against both battery contacts in the calculator for a few seconds. Put the batteries back in and turn ON the calculator. The display should say "Memory Clear". Reset the calculator as needed.

Second: is your calculator could have an open connection somewhere inside, maybe between the LCD and the PCB, and it will need servicing. One of the guys receintly posted his story of having to re-solder his do-it-yourself 32K memory chip exchange upgrade in order to stop his calculator from beeping, as he was not able to reset his calculator after his first soldering job. After re-soldering, he corrected an unknown bad solder connection and was able to get his calculator to comply with the above reset procedure.

I think the following is still valid.
You can contact Calculator Support:
Calculator Support,
1000 N.E. Circle Blvd.,
Corvallis, OR 97330, USA,
(503) 757-2004,
8:00 a.m. to 3:00 p.m. Pacific Time, Monday through Friday

Edited: 9 Nov 2003, 3:23 p.m. after one or more responses were posted


Mike Brady Thanks for the great help Mike, San Francisco. is a great town with lots of smart people. Oh, by the way, thats where I was born. Thanks again.


I have tried everybody's suggestions, bought new batteries, did the reset buttons by pushing down on the exit key and the squareroot sign key, shorted the battery terminals with and without batteries installed and it still beeps. Just a wonderful thanks to everyone for the suggestions. Great website you got here with responsive smart people all over the world. Maybe my last resort is to contact Randy Sloyer for repairs. Does anybody have his email address? Otherwise I will be selling it on EBAY ID (smatgo2pv) and buying a new one.

Steve in Seattle, The Boeing Engineer.



I just caught up with this thread and would like to clarify some points in Mike's post:

1) The 42S does not have a smoke detector feature. There is no beeping alarm to warn of low battery voltage. I don't know where he might have read that, but it just ain't so. The low battery alarm is an annunciator on the LCD, it does not beep. It is also not terribly reliable either. Just ask anyone who does a lot of I/R printing. The 42S will prevent you from printing due to a low battery but the low battery annunciator never comes on until it's too late to save memory contents in many cases.

2) On and SQR ROOT together do a soft reset with no loss of memory contents. It's only useful when you have a run-away looping program. A hard reset can be done holding down the E+ and XEQ keys together and then pressing the ON key. If that doesn't work, the of course the coin reset trick is the best way to start at ground zero.

3) A loss in connection between the logic board and LCD? Huh? What does that have to do with a beeping machine? Dead pixels maybe...

It has been my experience that a beeping 42S has a fractured solder connection on the external ram chip, typically pin 14 or 15, or that the ram is bad. It is the power-up self test that detects the loss of external ram and starts the beeping. A very simple test is to press on the back of the calculator directly behind the 4 and 5 keys then try turning it on while you press. If it powers up okay, you've got a cracked ram connection.

Dave has been kind enough to list a link to my website here in the "Repairs & Batteries" section. As it is my policy not to solicit repair work, I leave it to you to you to click through and find the details if you want outside help. If you know it's the ram connections and you're comfortable with resoldering a surface mount device, there is a very good piece in the Articles section on how to open a Pioneer by Paul Brogger.

PS: Are you the Boeing Steve I skied with in NZ back in '85?


Randy Your the man, the hard reset did it. No I am not the Steve you went skiing with. You just saved me the cost of a repair or a new calculator. Thankyou so much for great advice. I'm a Mechanical Engineer at Boeing and if you are ever in Seattle, I'll buy you a beer. Steve Mathews At Boeing Thanks again.


The Steve I skied with was a Boeing Structural Engineer. I guess the world isn't THAT small!

I would not discount the possibility that one or more of the ram connections are fractured. The power-up beeping is a sure sign. They do tend to be intermittent. Squeezing the case may restore the connection for days, weeks, months, who knows how long. It's one of the more difficult problems to find as you need at least 5 to 10X magnification to see the cracks.

Check out the used 42S prices on eBay, I think you'll find you'll want to keep yours in good running condition.


I couldn't resist adding a cheer to all of the above! I'm a 42s guy and have had the beeps once (after a calc was in checked luggage when flying). It was while ago so I was able to call HP service in the UK and was very nicely told about removing the batteries and shorting the contacts. It worked...though the "Memory Clear" message was not a happy sight.

Generally, I change the batteries once a year whether they need it or not...unless the total voltage is still right up above 4.5v. Checking batteries occasionally with a voltmeter, which is easiest to do while they are still in the calculator, has spared me any similar problems for a long time. I have discovered batteries with a total voltage around 3v still working the calc. nicely.

I think I've only seen the low-battery indicator twice in 10 years or so. The first time I just casually worked on (I was in the field surveying) and changed the batteries at the end of the day. The next time, on a different calc., I didn't even have time to switch it off before it went blank and lost its memory. This probably has more to do with the batteries than the calc., though, so now I always use good batteries.

The 42-s is a truly great machine...under rated, even...because of its Achilles' heel: when you have to re-program it.

Many thanks for the thread above,

Richard (in Athens)

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