HP-41 Fullnut question


I have a reasonably old fullnut HP-41C. It was rattling a litle and I discoveed it had a broken post. However, on closer examination I find that there may be something else missing, and one more detail that I am curious about.

Here is the calculator. The red bits are the things I'm interested in:

The first thing are the connections to the display at the top left corner:

Note that one of these appears to be missing.

It looks like the solder joints are broken, bit the calculator appeared to work correctly. Is there normally a link here?

I've fixed a couple of calculators with really weird display faults that turned out to be a poor joint in these jumpers, but I can't remember if they had three or four links in this position.

If it is, then I am amazed that this calculator appeared not to have an obvious display fault. If it's not, then the pads sure do look like they've been used!

The other thing is:

Note that the two boards appear to be hels together by nuts on the lower posts.

Do all fullnuts have these nuts? I know that the older C's I've repaired do, but do they all?



The answer to your questions are :

1. Three wires in the left hand group of display connections is normal, I have never seen four used on any fullnut, old or new.

2. Only early C and CVs had the nuts on the lower posts(~1979 - 1980/1). Newer ones used a slightly different case back such that the case back itself applied pressure to the CPU board to ensure good connection.



John is right, there are only three attachments at the left LED side. This had me confused once too.
As far as the nuts are concerned, these work alot better than the pressure from the case trick. I wonder why HP did not do them all this way. I had thought that it was a later mod rather than an earlier one.

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