HP25 Keyboard exchange

[c_d]

I have a HP 25 with a damaged keyboard (not all functions have readable label anymore) otherwise the keyboard works perfect. I found a different keyboard and tried to exchange it.

The result is different:
- Sometimes a key activation leads to nothing (0.00 remains in the display). Furthermore it is not possible to switch to the programming mode (0.00 remains in the display). Switching the HP25 off an on again the programming mode will be entered.
- Sometimes some keys works fine and other keys behaves as different function (for example 7 behaves like enter, 1 behaves as 4, 8 as CHS, 9 as EEX...)

Does someone have an idea?

HP25 SN: 1508SXXXXX
PN Keyboard PCB original: 00021-60002
PN Keyboard PCB replacement: 00021-80015

Chris