HP25C repair, help needed

[albertofenini]

(01-28-2019 11:35 PM)Geoff Quickfall Wrote:  Just for the heck of it, I don’t know how far into the restoration you are but I have some thoughts on restoration.

Firstly do as little harm as possible. Ripping apart the heat staked keyboard is a pretty major undertaking. The problem is reattaching the keyboard to the keyboard PCA.

this can be accomplished by removing as little of the heatstake as possible prior to the disassembly, then reheating / melting the heatsake back into a mushroom.

Others have tried mini screw heads.

My caveat is to isolate the keyboard and PCA then clean the board first in hot soapy water. If copper sulphate (battery corrosion on the contact domes) is suspect then a soak in a white vinegar solution followed by a rinse then drying thouroghly. The inside of the dome then is scraped by inserting a fine stiff wire in the pore on the keyboard PCA board and twirling it around. Introducing into the pore DeOxit red and work the key.

If these steps don’t result in a functional key then consider the major surgery.

See this link: Pores in various HP calc Keyboard PCAs

ALSO, the keyboard silk screening on the Woodstock’s is notorious for being faded and being wiped off. Dab the keyboard dry, do not rub it dry or you risk removing the silk screened labels.

Geoff

Thanks Geoff
I'm afraid we are already beyond that point ...
If you look at message #24 of this post you will see that we had to open the keyboard apart,
although we know it will be very hard to close it again.
However most of the copper traces on the plastic film were broken,
we will try to replace them with thin strips of copper tape.
If we will be successful in that we will think on how to put the pieces back together
Thanks for your help, always very welcome !