HP-25 resurection project

[Maximilian Hohmann]

Hello!

(12-01-2020 04:39 PM)wbvreeuwijk Wrote:  I do believe there are some components missing from the PSU. Details here: ... Based on other pictures I've seen of the HP-25 internals there should be some more components here.

Obviously the "non-C" HP-25 has less components (I guess the extra resistors keep the memory of the 25C powered when it is turned off). Here is a picture that I took just now from a normal HP-25. It looks exactly like yours!

(12-01-2020 04:39 PM)wbvreeuwijk Wrote:  Also some examination of the LED display. Not for the faint of heart ;-) ...

Wow, this looks very green inside. Here is a link to a photo of an HP-25C where the display connections are annotated (it was made by a forum member who unfortunately passed away some years back): http://home.citycable.ch/pierrefleur/Jac...25_WEB.jpg
The "K1" to "K12" connections are the cathodes of the individual digits and "a" to "h" are the anodes of the segments and the decimal points. With that it should be possible to check which segments are still working. Mind you that there are no original replacement parts. You may need to cannibalise another calculator of that series to fix yours...

You have certainly come across the website of "Panamatik" (also a forum member) (http://www.panamatik.de). He designed some repair kits for "Woodstock" calculators like the HP-25 and at one time even made some replacement displays. He might have some left if you are lucky.

Regards
Max