HP-41CX Port 1 and 3 temporarily malfunction

[JurgenRo]

The other day I plugged in the Games-Module into port 1 of my HP-41CX. The machine did not recognize the module (CAT 2). Same result for port 3 (CAT 2). Plugging the module in port 2, CAT 2 resulted in a weird display (flickering of some special characters, BAT annunciator on) followed by a blank display with a locked up machine finally.

Removing and immediately reinstalling the batteries cured the malfunction: CAT 2 showed the Module in any port. Fortunately no "memory lost" occured either.
What could have been the reason for this misconduct?

[rprosperi]

(11-23-2020 08:13 PM)JurgenRo Wrote:  The other day I plugged in the Games-Module into port 1 of my HP-41CX. The machine did not recognize the module (CAT 2). Same result for port 3 (CAT 2). Plugging the module in port 2, CAT 2 resulted in a weird display (flickering of some special characters, BAT annunciator on) followed by a blank display with a locked up machine finally.

Removing and immediately reinstalling the batteries cured the malfunction: CAT 2 showed the Module in any port. Fortunately no "memory lost" occured either.
What could have been the reason for this misconduct?

If other modules work fine in all 4 ports, then the Games module you are using is defective, or perhaps the contacts need to be cleaned.

It is rare, but 41 modules do go bad - I suspect there are multiple failure modes, and of course how they have been treated for 40+ years is also a factor.

The simplest way to clean the contacts is to fold some fine (500+) sandpaper and run it gently over the inner contact surfaces of the fingers (which will touch the board inside) of the module interface. You could even try cleaning the contacts with alcohol on a Q-tip before resorting to sand paper.

Don't press/rub so hard w/Q-tip or sandpaper that you bend the shape or position of the contact fingers! If you look into the interface, you can see the fingers are nearly touching, only apart enough to grasp the contacts on the board inside the 41 I/O sockets.

[Allen]

It is also possible that one of the screw posts for the calculator has broken internally. If that is the case, some of the connections behind the battery block may be intermittent. This can effect some but not all ports for the plug in modules.

The description of removing and reinstalling the batteries to fix the issue could have slightly moved the battery contacts, and seems to fit the hypothesis that perhaps the posts/case halves may be slight loose.

Have you tried GENTLY wiggling the case halves near the module ports with no modules or port covers installed? Be careful with testing this.

[twoweims]

This happened to me after a 41CL Conversion. I had a cracked upper post and did not realize it. It is working fine now after repairing the post.

[JurgenRo]

Thanks for your inputs! I don't think that the malfunction comes from a hardware issue like broken post or bad module contacts though because the failure happened to occure with every module I tested and all the modules work after the batterie removal and reinstalling procedure just fine. However the explanation

(11-24-2020 04:00 PM)Allen Wrote:  The description of removing and reinstalling the batteries to fix the issue could have slightly moved the battery contacts, and seems to fit the hypothesis that perhaps the posts/case halves may be slight loose.

sounds quite reasonable.

(11-24-2020 04:00 PM)Allen Wrote:  Have you tried GENTLY wiggling the case halves near the module ports with no modules or port covers installed? Be careful with testing this.

No I did not because everything is working fine (at least for now) and I do not want to go the risk a broken post by this