HP27 Restoration (Lots of Corrosion)

[teenix]

(04-06-2022 11:44 AM)calc-calcs Wrote:  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 clean.

Thanks again.

There is a bit of difference in the 29C and 27, mainly ROM/RAM chip count. The 27 has less and the power on reset setup is a bit different. The RAM chips have continuous memory support in the 29C also. The ACT is mostly wired the same.

Tony Duell's circuit for the 27 is here:
http://www.hpcc.org/cdroms/schematics5.0...k/hp27.pdf

Teenix schematics
http://www.teenix.org/classSchm.zip

If you end up stripping the circuit board down to clean it, and if you have time, perhaps you could post or send me some pictures of the bare board from both sides with a light source behind as in you other pics. I might be able to re-engineer the board design and add it to the ones on teenix.org

cheers

Tony