65: Slight squeaks from the card reader

[Dave Britten]

(01-09-2020 02:12 PM)burkhard Wrote:  There is no clutch in any of the 41/65/67 card readers. Somebody said that long ago and for some reason it has stuck, but it's quite incorrect. What people call the "clutch" is the motor output shaft, a coupler, which rather than being completely rigid, has an elastomeric bit in its middle between two metal ends. The idea of such of coupler is to slightly dampen out the pulsations in the motor output drive.

The elastomer in that shaft, like that in the infamous drive wheel, can fail over time which can result in slippage from one side of the shaft to the other. Such slippage *might* be why people call it a clutch, but that's a mistake. It's not supposed to disengage, slip, and re-engage (like a clutch would). When the coupler in the card reader does that, it has failed. Geoff Quickfall has a video on YouTube that nicely shows how he has done a repair. He uses electric wire insulation as a new elastomer. People might squirm thinking that is not the exact specification as the original elastomer and while they are probably right, I suspect the tolerance of what "works plenty fine" is pretty broad.

In any event, the "squeak" you hear might be that coupler starting to give up the ghost. Is the squeaking happening in concert with a jerking feed of the card into the reader? If the shaft is slipping, that will be reflected in the card motion. Personally, I probably would live with a little noise unless it fails completely or you had reason to open the calculator for other reasons.

Ah, I see, thanks for clarifying. I'll see if I can dig up Geoff's video.

The card motion is nice and smooth, with no evidence of jerking or slip on the coupling, so it's probably just a bit more noise from the motor, or maybe even something else that's a bit loose inside the case vibrating along with the motor. The noise is perfectly livable, I just want to be sure it doesn't mean that something is out of whack and going to cause premature failure somewhere in the drivetrain.

I did open it up already to clean all the key contacts (and the key response is absolutely beautiful now), so I'm not afraid to go in again if there's something else that needs a small tweak.