Rotato

Today it's the MC-303 back on the bench.

After I had initially repaired it, I noticed that the rotary encoder was a little skippy. It would sometimes miss steps, go backwards, etc, which indicated that it likely had some contact issues inside it. So, apart it comes.

We'll need to remove this happy little camper from the board.

And luckily this unit is old enough to have delicious leaded solder, which slurps up so nicely.

To properly clean the contacts, we'll need to open it up. They're not exactly designed to be opened, but it's relatively safe to do once or twice.

With the limiting factor being how many times you can bend these tabs back and forth before they fatigue and break off.

But given it's lasted this long before failing, it'll probably be a good while longer before it fails again. and needs another disassembly.

Inside we have three contacts and a spoked metal disc. One contact rides around the solid part of the disc making constant contact, while the two others ride around the inner and outer spokes respectively, making contact 90 degrees out of phase with each other.

At least that's what they're supposed to do when nothing's getting in their way.

Hmm, what's this? Zoom, enhance!

Well that's no good, there's a little flake of plastic sitting on the back of one of the contacts. If that got between the contacts and the disc it wouldn't function very well. I wonder where it came from?

Yes, I wonder indeed. It looks like a thin ring of plastic was overmolded onto the outer circumference of the spoked disc, and it has over the years cracked and broken away. Well, that explains things, better clean out the shrapnel.

That's looking much better. Now it's just a matter of slathering up the shaft with some friction grease and getting things back together.

And together it goes.

As does the rest of the machine.

And I'm happy to report that the encoder now works perfectly.

I do have one other task on the plate for this unit...

But it will have to wait for another day.