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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

(07-10-2015 11:56 AM)c_d Wrote: [ -> ]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

To my knowledge the keyboards of all 20s models have the same schematic and are interchangeable without restrictions. Even the different layout of a HP-29C keyboard can be used with HP-25 because electrically they are the same.

The switch for programming mode is not connected to the keyboard matrix, it is a separate pin.

If both functions are affected, it could be a short somewhere or a ground contact missing. Check the contacts to the main board?

Bernhard