|Re: WOW, but...|
Message #5 Posted by Jeremy on 19 Mar 2003, 7:58 p.m.,
in response to message #3 by Michel Beaulieu
"But now how can i "open" the keyboard to clean the switch? it seems to be "plastic soldering" in place like my HP-41. I never try to open my 41 keyboard but i need to open this 25 : how to do it safely? "
Be warned, this information is completely from memory and is assuming that the HP25 is similar to the HP45 that I have. So work at your own risk ;)
There are 6 or 8 screws that hold the whole circuit board assembly to the front half of the calculator molding. If you take these screws out, it should easily just lift out. When *I* did that, the springy brass contact that completed the power circuit just fell right out. At the time, I didn't know what it was, I had to look around for a bit to figure it out. At that point, you will see that the formerly shiny contact points on the springy brass contact and the contact points on the circuit board are completely dirty instead of nice and shiny and clean. So then, you can just clean it off with rubbing alcohol and a clean, lint-free cloth. (I used an old clean sock) I just put my finger in the sock, dip it in rubbing alcohol and rub it until it's pretty clean. Then, put it all back together and away you go!
While I had mine apart, I also replaced the plastic sheet that keeps the keypad contacts relatively sealed, as it was cashed. I just used a plastic wrapper that was used to package some Radio Shack battery connectors I bought and trimmed it to size.
Using an old toothbrush, (dry) I also cleaned out the inside of the enclosure and the keyboard. It is amazing how much junk accumulates in the corners in 30 years...
It was great fun to work on that. It was designed with technicians in mind and it shows. If the cicuitry was fried, I don't know that I would be able to track it down, but many times it is something much simpler. Those simple things can intimidate lots of people and they shouldn't.