Some thoughts on my first 82104A repair

[flimshaw]

Hello there! First time posting, just in the hopes this is helpful for someone.

I recently successfully repaired a very gummed up card reader I bought to save programs from my 41CV using the excellent documentation on the museum and also over here.

I had to do it a few times, after trying my luck with the smallest o-ring I could find at my local US hardware store. Things seemed to run smoothly, and I was able to read some cards that had come with the reader and had old programs on them, but writing new cards would consistently fail at the end. I took a guess that the ring was a bit too big, and thus was running too fast and cutting off the final part of new programs, but was perhaps slow enough that older programs could (generally) be successfully read.

To confirm that data was being written and check for differences with older cards, I used this magnetic viewer and it was actually super helpful. There was a bit of difference on the tail end of newer cards, but information was indeed being clearly written. Here's a photo, very handy (and fun) for diagnosing magnetic data storage.

   

In the end, I ordered some proper 005 size o-rings, but also in my impatience disassembled the card reader once more, and tried to sand down the o-ring I had just a bit. After reassembly, it is now working pretty well! I probably will go in one last time and put a proper o-ring on, and attempt to actually get the spring clips in place (gave up on this until I knew I wasn't going to have to take it apart a final time).

Anyhow that's all, hope it is helpful or interesting for someone! One thing I've noticed too is that the battery on my calculator seems to run very low if I leave the card reader plugged in, even if the calculator is off. Is that the expected behavior or is there something amiss that I should look into? Also, not the best picture, but to my eye the head here looks awfully worn down, though I've mostly worked with cassette tape machines. Is it difficult to source new ones that are a match, or is this a fairly generic stereo tape head?

   

Thanks all,
-Charlie

[born2laser]

Seems you took the same path as I did to get back into calculators, I second your recognition of all the useful information posted here.
Not a collector myself, just want to take my 40 year old 41CV to the limits, and been buying the toys I could not afford when it was new.
Just a comment that may be useful to others, I did not use o-rings, but I found this tubing in McMaster-Carr that did the trick for me
https://www.mcmaster.com/catalog/129/161/9627T13

[John Garza (3665)]

Back in the 90's model airplane fuel line tubing was the way to go. However, the new stuff made in China is of lower spec - meaning the inner circle (hole) is not always concentric with the outer tubing. This of course means the chance of uneven card motion, even slipping. To some degree, adjustments of the axle will help, but the better solution is to go to O-rings which are higher spec. In particular the square profile O-rings work well and provide a larger gripping surface on the mag cards. Using 2 circular profile rings tends to leave 2 tracks of smeared graphite (from pencil marks) over the card after a few uses. I use soft lead (esp 'film lead' type) for marking cards so I don't damage them and leave impressions. I've forgotten how many of these I've done over the years (65/67/97/41C), but they are all similar mechanically.

And yes, there is gold in the archives here!

-John

[Johnboy]

I've had good success with silicone tubing that has slightly oversized outside diameter. To avoid the concentric issue, and to "mill" the tubing to the correct diameter I use a drill press. Using a Dremel like mandrel, I slip the tube over the mandrel shaft and push it up to the drill press chuck. I do put a o-ring between the tubing and Dremel mandrel head for grip to make sure the tube spins with the drill press switched on. That setup holds the tubing firmly. I can use a box cutter to slice through the rotating tube to get and even cut for the length, and an emery board (nail file thing) on a longer piece of timber which I lever off the drill press stand to get a nice square/even grind/filing/milling/sanding of the tube. That method also leaves a nice grippy surface on the tube.

Cheers,
John