Switching Things Up

So recently I got the urge to actually make a little music. For reasons I may or may not explain in a future blog post, I decided to use my MC-505 to do the job.

I probably should have grabbed my QY100 instead, because as soon as I powered on the MC-505 I was reminded that I still definitely needed to replace the main key switches for the sequence/keyboard buttons along the bottom. They were double-triggering whenever I released a key, which was really not helpful for trying to make music, as you might imagine.

So, apart it comes.

The black switches with the grey silicone domes are the culprit. They sit underneath the black and white plastic "keys" and do the job of actually being a switch. The silicone rubber dome makes them a little more squishy and mostly silent compared to the usual clicky tact switch, which is appropriate for this function in a musical instrument.

Anyway, I happened to buy a whole bulk bag of replacements from some mysterious source in the far east, so in they went.

I put everything back together and powered the system on and to my delight the triggering was now very solid with no bouncing and multi-triggering. Unfortunately I was reminded of the two OTHER reasons that this box was still sitting in the repair queue: the 8 main part mixer sliders were rather dramatically misbehaving, and the main jog wheel encoder was barely functional.

I'm pretty sure both these issues can be solved with a little careful disassembly and cleaning, but that task would have to wait for another day. First, I needed a little break to touch some grass.

Mmm, greenery.

Anyway, since the MC-505 still needed work I grabbed my MC-303 and set to work hammering out a tune.

This lasted for all of about 3 seconds before I remembered that it too needed a new set of key switches. Well, I've got the soldering iron warmed up so let's get to it I guess.

Much like the MC-505 this involves removing literally every component in the entire system. But then it's out with the old...

And in with the... also old? You see, I'd found a source for some new-old-stock switches that exactly matched the originals in the MC-303, and I wanted to try them out.

You can see the new, NOS and original switches lined up here from left to right, and the difference with the new switch is pretty plain to see.

It would still probably work, but there was one issue with the new switches that was giving me pause: the contact resistance.

Here's the new switch when pressed.

100Ω is pretty trash tier for most switches, but for a carbon pill switch without any additional coatings to improve conductivity it's kind of par for the course.

So let's compare that to one of the original switches.

It's a bit on the high side, but 3Ω is an order of magnitude lower resistance than the candidate replacement. This wasn't too much of an issue on the MC-505 since its original switches were reading more in the 100Ω-ish range too, but something felt wrong with replacing a low resistance switch with a high resistance one in the MC-303.

The NOS switches, despite being 30 years old, were obviously built different from the new switches.

That's more like what I expect to see from a switch that's working properly.

But that leads us to another problem, which is that these switches have been lingering around for 30 years, exposed to the atmosphere, humidity, and so on, and that's taken its toll on the leads.

Solder isn't going to stick to that black, sooty oxidation no matter how much heat I use. So I need to scrub it back to clean metal with a wire brush first, then tidy up with some isopropyl alcohol. Here's a little before-and-after.

The leads were still a little disagreeable when soldering them but I think I managed to get a solid joint on most of them. I wouldn't be surprised if at some point down the line some of the solder joints fail, but that's a future-me problem. For now they're all working reliably.

And after all that I still ended up using my Yamaha QY100 instead.