HP-25 resurrection adventure – Part 1: The Keyboard

[Dreato]

"display goes dark for about 0.5s and then shows "0.000000000"."

I had this identical behavior on one of my 25s after the Panamatik ACT-E conversion. The 'external' 25 ROM gives the behavior you described. The 'internal' ROM (on the Panamatik chip) works perfectly. It's the ACT chip. Put the new ACT-E in. If you get this behavior, hold down EEX while switching on. This toggles between internal and external ROM.

Regards,

Dave