Restoring HP25 S/N 1702S13138 - Very strange take a look

[albertofenini]

ciao Ignacio, thanks for the idea !
We are trying to rebuild two units, one is an HP-25 and one is an HP-25C.
Both units have a good PSU, display and keyboard working, ACT and Rom working, bad RAM
We have purchased this last unit with the hope to recover a working RAM for the HP25 project
and we were thinking of putting a Panamatik kit in the HP25C, since finding a donor for
an HP25C is more difficult and more expansive.
However, when this came in, we thought that cleaning the corrosion would have been enough
to bring it back to life and us it as a whole logic for the HP25 project.
Honestly, we could just de-solder the RAM and see if it is a good donor for the HP25 project,
but we are curious people and we want to learn why in a unit apparently in good shape the Vdisp is wrong.
Will keep testing on it and will see, however we also want to try the Panamatik !

BTW, do you have any idea why Vdisp could be wrong ?
Thanks for help