HP75D battery design

[Hans-Peter]

I recently bought a HP75D without battery. According to relevant information a Classic Pac should work. Unfortunately the contacts are not where they are on the Classic Pac and there are 3 contacts. Can anyone tell me what the third contact is for?
If I connect a power supply with 4V to the two left contacts, then the computer can be switched on and it seems to work. But I have not tested the card reader yet.
   

Greetings Hans-Peter

[rprosperi]

(11-02-2020 08:40 PM)Hans-Peter Wrote:  I recently bought a HP75D without battery. According to relevant information a Classic Pac should work. Unfortunately the contacts are not where they are on the Classic Pac and there are 3 contacts. Can anyone tell me what the third contact is for?
If I connect a power supply with 4V to the two left contacts, then the computer can be switched on and it seems to work. But I have not tested the card reader yet.


Greetings Hans-Peter

Classic battery packs work fine, the 2 leftmost contacts are in the correct place.

An engineer that worked on the 75 product line confirmed at HHC a couple years ago that there was short-lived plan to introduce a new battery design and the 3rd contact was somehow involved in the charging of the new design, but it was abandoned just after the 75 design added the contact. Some late 75D machines don't have the 3rd contact, but it's not clear when the configuration changed.

[Hans-Peter]

Thanks Bob, you were my help.

Hans-Peter

PS: I haven't had time to test the Spicedisplay yet.