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.

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.

Pure 90s Cringe

Since it was recently 3/03 day, which is one of the few "funny number" days that both Americans and Europeans can agree on, I decided to pick up a 303. Not the legendary Roland TB-303 bass synthesizer, the device which single-handedly launched the entire musical genre of Acid Drum and Bass, but instead the Roland MC-303 groove box which launched absolutely nothing of value.

Which is a bit odd, considering that this one box could easily substitute for a TB-303, while also stepping in for much loved drum machines like the TR-808, TR-909, TR-606 and CR-78, while still having room left over for 6 more (admittedly rompler) synth parts.

But its cardinal sin was, I think, that it came with too many preset patterns, which led people who consider themselves serious musicians to dismiss it, putting it in the same category as those home keyboards that play a whole song when you just hold down a single key. Thus it was relegated to the DJ table of tweeners' birthday parties where they could dance to its slightly too repetitive preset beats.

That said, many products that Roland has produced over the years, like the aforementioned bass and drum machines, were initially considered failures until they were unloaded in thrift shops and sold for $100 to a new generation of aspiring musicians who would then go on to produce great, genre-defining works with them.  The MC-303 is no different in that regard. Well, at least the part where I picked it up from a thrift shop for $100, I don't think anyone's made any great, genre-defining works with one. (Though the MC-505 that came out later as its replacement did see some success)

Anyway, all that aside this box was only $100 because it doesn't work, so let's crack it open and see what juicy goodness awaits us inside.

Ah yes, juicy goodness. Some obvious signs of spilled liquids on the bottom case there.

And it's on the main panel PCB as well, here's a few extra juicy spots.

And on the top side things are looking kinda sticky.

When I did the initial tests the unit powered on and most functions seemed to work, but the buttons in this corner in particular were largely nonfunctional, including SW27 which is the 'Play' button. Rather important one, that. Checking the resistance showed a reading of hundreds of ohms with the switch pressed, so they obviously need replacement.

So let's get the plastic key caps off and bust out the IPA.

And with a little scrubbing, things are looking dramatically cleaner.

This cleaning didn't bring the switches back to life, of course, and these rubber dome 8x8x5 switches in particular are a bit tricky to find replacements for.

The original switches are made by Panasonic, and Roland was very fond of using their switches for a while in the 90s up until Panasonic stopped manufacturing switches because they were so incredibly bad at it. Other manufacturers still make similar switches, but most of them are semi-anonymous Chinese factories that are hard to pin down the identity of and even harder to order from. Luckily there's still some new-old-stock of the QJJ05Q switches floating around, so I ordered some of those off eBay and we'll see how things go when they arrive.

The other tact switches are thankfully much easier to find, they're just bog standard 6x6x5 clicky switches with the only peculiarity being that they're 2-pin rather than the more common 4-pin variety. I already had a bag of them laying around that I was planning to use for my Roland JP-8000, but I didn't feel bad pilfering them as I can always buy more.

So, nothing to it but to do it.

35 old crusty switches come out...

And 35 shiny new switches go in.

Then everything goes back in the box, which has now been cleaned, for a quick test.

Don't worry about half the display being blank, that's just due to the really slow refresh rate on the LED matrix.

And with the knobs back on and the case buttoned up (and with the picture timed to show the other half of the display lit up)...

All the replaced buttons are working perfectly, and I was able to validate the full functionality of the system.

Quite surprisingly I didn't need to replace or service any of the potentiometers along the top. It's really common for them to get damaged since Roland for some reason didn't see fit to actually bolt them down to the solid metal front panel, so a suitably forceful sideways strike can basically split the potentiometer clean in half. I guess I'll count my blessings on that one.

Anyway, all that's left to do now is wait for the NOS switches to arrive so that the 3-4 dead keyboard keys can be revived and it'll be good as new. There'll be nothing left to fix or improve...

Or will there be? Stay tuned.