Problem with HP 25

[Steve Simpkin]

How are you powering the calculator. The multi-decimal point low voltage indication can come on if the voltage source drops while under load.

For the issue with keys 4 and 5, there may be contamination under the contacts for those two keys. Most Woodstock and many other HP models have a small hole on the keyboard circuit board under each key. Many people have had some success with using some very thin stranded wire, spread out and inserted in the tiny hole in the PCB under a malfunctioning key. Put a drop of 99% isopropanol into the hole first then insert the wire bent at at angle and use this to brush around on unseen side to the PCB. You can try Deoxit too.
The following post by Geoff Quickfall has some example pictures that show the holes under the keys on several models. The rest of the three page thread is interesting reading too.

https://www.hpmuseum.org/forum/thread-59...l#pid52993