My HP 45 has developed a problem whereby it doesn't give the correct answer for some functions. The regular functions (sin, cos, conversions etc) are OK but tan and arc sin, are cos etc are incorrect. Tan sometimes returns a numerically correct but negative answer while arc tan always gives nonsense. Asking for the square root causes the display to flash with zeros. Some of the other keys (sin and 2) have also stopped working. Does anyone have any thoughts on repair ? Could it be the keyboard or are the chips giving up ?
Thanks
Charles
The non-working sin and 2 keys can probably be easily remedied. You will need to completely disassemble the calculator, general instructions are here. Below is a picture of a disassembled 35, the 45 has the same physical construction.
You need to clean the contacts on the key contact board in the middle of the above picture. The contacts are the metal strips that form the arches across the board. Cut some strips of fairly stout paper 3" long and maybe 3/16" wide (75 mm by 5 mm if you prefer metric units). Soak a strip in a good contact cleaner, and stick it under a contact arch. Press down on the arch and pull the strip through. Repeat several times on each contact. Reassemble and test. If you are lucky, the other anomalous behavior is due to key contact problems that the cleaning will fix. If not, it sounds like a more serious problem on which I can offer no help. While you have the unit open, clean and lubricate the ON/OFF contacts. You can also soak the keys in "Fantastik" or "Formula 409" or some other general household cleaner to get any grunge off.
Good luck, let us know how things go and post again if you have any questions.