HP-67 - polarity of wires to keyboard/display board?


I was disassembling an HP-67 and the two power wires that go to the keyboard/display board popped out of their sockets before I had noted which goes where. Based on how the wires are arranged it looks like the black wire goes to the upper connector (board oriented with the display at the top) and the red goes to the one below it?

I couldn't find a photo that was clear enough to be sure, so if anyone knows or can point me to a reference, I'd be grateful.




Here is a quote from Steve Loboyko's excellent post:

67 posting

Remove the very thick keyboard pad from the middle plastic of the sandwitch. There are two Augat sockets that connect two wires to this board. They are NOT soldered. NOTE THE COLORS OF THESE WIRES AND WHERE THEY WENT BEFORE REMOVING. A MISTAKE HERE COULD BE ABSOLUTELY FATAL TO THE CALCULATOR WHEN REASSEMBLED AND POWERED. I would rather not give you the colors or positions here because this could vary during the production run, but on my 3 67's, the black striped wire was at the top, and the red striped wire was beneath.

I personally have had all wiring described as above, but substitute striped for solid colours.

Maybe Randy can be more specific on this however Steve is correct. There are many differing production runs and production sites.

Cheers, Geoff.


Thanks Geoff! I'll see if I can confirm that arrangement by doing a little circuit tracing to a known Vcc or ground somewhere.



Hi Bob,

I have a schematic that I prepared when I worked on the card reader in my HP-67, and it shows a black negative wire connected to the top right side of the main keyboard pcb and a red positive wire connected directly beneath it. These wires go to the center negative pin on the ac adapter receptacle and the 5vdc positive pin respectively.



Mine turned out to be the same arrangement. Thanks very much Geoff & Michael.

And I got the card reader to work again! Guess I'll be building a battery pack tomorrow.


Edited: 14 May 2011, 1:37 a.m.


Production runs change. The caution is 'what applies to one calc may not apply to another.'

Anecdotalely, but with no direct evidence, I have been informed that the wire positions have been moved during differing production runs.

I have three different coloured wires for power supply in my 65's and 67's from vertical striped to solid. I have yet to see changes in the positioning but have seen that in other boards from other calcs that have undergone revision during production.

That is why I say, don't assume they are all identical.

Cheers, Geoff


It's simple to determine polarity on any classic, any version. The positive terminal always terminates on the left side pad of the power switch.

Also, you can sanity check yourself using Tony Duell's excellent crib sheets on all the classics in the archives. HP-67 Internals

Edited: 14 May 2011, 8:46 a.m.

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