HP27 Restoration (Lots of Corrosion)

[calc-calcs]

(04-06-2022 08:41 AM)Jonas Sandstedt Wrote:  Hello,
Good work, it seems like a real challenge and it is interesting to follow.
Perhaps you already know that, but you can find schematics for HP-27 at
http://www.teenix.org
and a service manual for HP-29c at
https://literature.hpcalc.org/

It might help.

best regards
Jonas

Hello Jonas,

Thank you for the information. However I looked at the teenix.com website that you indicated for the HP-27 schematic, but the only link there related to this model seems to be for an emulator. Not sure if I missed something? If so could you possibly provide a direct link to the download?

I already had the HP-29C service manual for some time, and looked at it yesterday to compare, but the board layout in the ACT area is quite different. And at least in my copy of this manual there is not even a PCB trace layout, only parts layout on a blank board, and the schematic, which may be of some help.

Also compared the traces under the ACT with pictures of one of my HP-25 back from when I was working on them and had removed the ACT and RAM chips, and traces seem also mostly different. Seems I am going to have to create my own PCB trace layout, at least I can still see it quite clearly when shining a light on the opposite side of the board. At least the solder side traces look quite healthy and clean. Some holes of the chip pins appear to be clogged in the pictures bellow, but its just that not enough light was shining into them. At this point all thru-holes of both chips are reasonably clean. Will go over them again before installing the low profile socket strips.

Thanks again.