HP15C On Button won't respond

[GreyUser]

Run the self test which checks that the program in rom is valid. The test reads all of the rom and calculates a checksum and verifies it matches the original checksum stored in the units rom. If the checksum matches, all the segments in the lcd display will illuminate.

The keystrokes required to test are outlined here: https://www.rskey.org/~mwsebastian/selft...tm#voyager

If it does not pass self test, it is time to remove the case back and have a look. You peel the four feet off and remove the four #1 Phillips screws underneath. Lift a corner of each pad with a round wooden toothpick to avoid scratching the case back.

Once the screws are loose, carefully lift the back off the front half, looking for two very fine gauge wire coil springs that electrically connect the front metal aluminum keyboard surround plate to the case back aluminum plate for ESD protection. They are approximately 1/16” (1.5mm) in diameter, and different lengths, approximately 3/8” and 1/2” (~8 and 12mm) long. The long one lives in the hole by the battery box in the upper left quadrant, the shorter one in the lower right quadrant near the edge of the case.

Once open, count the black IC packages. There is still hope if it is a three chip unit as it’s most likely a fractured solder joint. You’ll need at least 5x magnification to see the failed joint if your eyes are the age of a typical RPN user. Reflow the failed joint(s) and it will be good for another thirty years.

There’s less hope for a two chip unit but have a look anyway, corrosion or a failed solder joint will cause the behavior you describe but a failed rom is more common on two chip units.

If you don’t want to open it, I should be able to tell you if it’s a two chip or three if you post the first five digits of the serial number. I don’t have super-easy access to that database but can get to it if it helps.