HP 42s Machine Reset Problem


I have HP42s calc., I use it every day. But today when turned on Machine Reset appears while continual beeping. Then it stops. I attempt to use and again interupted by a machine reset display. The first one cleared all my progs, so i've tried clearing all memory and restarting and running a self check, no success same prob. I have not replaced batteries, but there is no Low Battery indicator on. Any suggestions would be appreciated. Thnx Shawn


My experience has shown the Low Battery indicator to be an unreliable indicator of battery condition under normal operation.

Try enabling the IR printer port and sending the stack to printer. If the batteries are low, it will indicate "Batt Too Low To Print" and disable the printing as the IR port uses considerably more battery current than normal operation. This is a more reliable test of battery condition, but not a guarantee.

Replace the batteries if you have no means to measure the voltage.


The HP42 can even start beeping suddenly (in the middle of the night) to indicate that the batt is low.

Fresh batt and the problem was over......



I've replaced the batteries, no effect


Well, what we now have is the classic 42S owners nightmare. There are several possibilities, none of them good. In decreasing order of possibility:

  1. Foreign gunk (soda,coffee,etc) inside the unit or keyboard. Repairable.
  2. The 8K RAM is bad. Repairable.
  3. A failed solder connection somewhere in the machine. Repairable.
  4. The CPU is shot. A very bad thing, not repairable.
I don't think there is anything else that can be done without opening it up. Anybody else care to weigh in on this one? I'm open to suggestions.

My tip (if not already given by s.o. else):

Remove the batteries, take a metal paper clip,
carefully short the battery terminals for one or two seconds, re-insert the batteries.
Try to turn the machine on.

If that doesn't work,
then short the terminals with the batteries in
for a short moment, say part of a second.
Try to turn the machine on.

But: NEVER NEVER put in the batteries with wrong polarity!
This could really damage your 42S,
at least on the 48 series calcs it does.
In that case the calc will drain the batts in two days...


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