HP 42S - Problem


Hi everyboby

I’ve found in a flea market an HP 42S in excellent cosmetic conditions. When I inserted batteries and turned it on I had no display and all keys (except ON) only played a beep when pressed and screen remained empty. The only way to turn it off was to remove batteries.
Pressing keys randomly I could see sometimes “Memory clear” on the first display line and the value of x register “x:0” followed by other figures I don’t remember on the second one. The batteries are good because they make an HP 12C and an HP 32S work fine.
I’ve tried all tips found here (and in the archives) and no way to make it work. Things I tried were :
- shorting battery terminals without batteries,
- E+, XEQ ON keys sequence,
- Reset key sequences as indicated in the owner manual.
I must add that the top of the right battery terminal is broken. Normally it looks like a reverse P and in my case it looks like an I. However, contact is made as I can hear beeps and see that screen is powered on.
Is contact surface important? Does anybody here have any idea on how to make it work?



Hi Michel,

have you tried the self test?




First of all thank you for your quick answer. Indeed I have tried these tests but without result. The fact is that when I press any key I ear a beep. For instance if I press 7 I ear a beep and I don't see 7 on the display. Even, I can't turn off the calculator using keys because [SHIFT] also plays a beep. In such a case, I'm not able to know if calculator freezes at boot or not. I'm quite desperate...



I'm no expert, but it sounds like your unit has some sort of internal problem, i.e., it's not just a matter of clearing the memory or resetting it. If and when you decide that you have nothing to lose, Paul Brogger has written a couple of articles regarding how to disassemble Pioneers, see here and here. If you are lucky, perhaps it is a problem with the "zebra stripes." If you are unlucky, it is a keyboard problem.



Thank you Jeff.

Opening the HP 42S would be the last solution because I have no skills at all in electronics (usually everything that works I open doesn't work after. I'm a kind of Attila ;-) ).



I have a 27S with the same problem. Leaving the battery out for more than a year didn't solve it. My best guess is that the electronics has suffered from ESD damage.


Hello !!!

Is there any means (without opening) to solve this ?


Bonjour Michel,

ESD means electrostatic discharge. If this is the cause of what you see, there is no way for you to repair this.




Hello Walter,

Thanks, so I just hope it's something else. :(



Perhaps the tantalum decoupling cap has gone bung and is causing odd behaviour?

Try putting a 100uF cap across the battery terminals.

Internal shot for your reference:



Hello !!!

Can you be more specific because I know nothing about electronics. Should I have to solder something in case I open the case ?



Can you be more specific because I know nothing about electronics. Should I have to solder something in case I open the case ?

You just need to hold the capacitor across the battery terminals. Make sure you get the correct polarity though, it should be marked with either a minus symbol on the case next to the corresponding negative lead, like this:

Any electronic component shop should have one.

It's a long shot, but if you are out of options...



Hello Dave,

Thank you. I will ask some friends of mine for capacitor.




I'm a lucky guy. My wife found last saturday 2 HP 10B for 10 euros at a flea market. I think I will try to open one of them and then may be will open the 42S.

Thanks for your help.


Possibly Related Threads…
Thread Author Replies Views Last Post
  42s questions and 42s vs 35s snaggs 13 5,247 09-19-2011, 02:44 AM
Last Post: snaggs
  A new 6-problem challenge (free42 or 42s) Allen 22 5,319 06-12-2011, 05:56 PM
Last Post: Allen
  Hp-42s display problem aj04062 9 2,859 02-27-2011, 08:36 AM
Last Post: aj04062
  HP-42S work-around for sticking to low contrast LCD problem Lyuka 2 1,129 02-01-2010, 01:25 PM
Last Post: DavidShenk
  42s Statistics Problem Norman Dziedzic 11 3,027 12-06-2009, 11:43 PM
Last Post: Thomas Okken
  An HP-42S fix success, and a contrast problem DavidShenk 19 4,383 12-05-2009, 10:17 PM
Last Post: Lyuka
  Re: 42s Screen problem Alan 0 764 06-06-2007, 02:33 AM
Last Post: Alan
  42s Screen problem Alan 3 1,205 03-18-2007, 04:04 PM
Last Post: Randy
  42S Problem - Switches off straight away. David L. Jones 10 2,380 11-25-2006, 04:12 AM
Last Post: David L. Jones
  42S Programing Problem Trent Moseley 7 1,787 03-21-2005, 10:44 PM
Last Post: Chad Wagner

Forum Jump: