Making Waves

Right now my function generator only makes wave. As in singular, not plural. This is because it has only one output hooked up to only one DAC board.

But I'd like it to make waves, plural, and there's room on the front panel for a second set of outputs, and room inside for a second DAC board. So I got to wondering: can I simply install another DAC board to enable the second set of outputs? The internet holds no clues on this matter, and it's not addressed in any detail in the service manual.

So let's find out the fun way!

For the record, this board is HP part number 08904-60203.

And it's supposed to have a shield on the back but for some reason eBay scrappers always seem to pull it off and discard it, but oh well it'll be fine for my uses.

Anyway, as we can see it's identical to the one I already have.

So let's stick it in and see what happens.

Now I don't (yet) have a second pair of SMC to BNC cables, but the "Low" output is actually just a floating ground that you can bypass to chassis ground, so it's not essential for most of the uses I have, and certainly not essential for testing out if the two boards will work together, so I can temporarily reroute it to the second board.

The other connection I need is a 12 inch 34-pin ribbon cable, which is very easy to source.

Ideally this cable would have one of the connectors flipped around to the opposite side so that the ribbon cable exits the other side of the connector, but it'll work just fine as-is.

Routing this cable is probably the most difficult part of the install. I had to loosen both the DAC board and the main board on the other side of the chassis and then wiggle the cable in from the mainboard side.

But I got it in there.

Then it's just a matter of plugging the board in, snapping it into place on the standoffs, and we're ready to tickle it with electrons and see if it'll dance.

So good news off the bat, without any extra configuration it lets me now select Out2 as a destination.

And if I take a peek at the scope...

It is, in fact, making waves (plural)! Perfect.

Now this does leave one minor issue, which is that I don't have any 19mm spacers to go between the boards to prevent them from jiggling loose and shorting out against each other.

But then, I do have a 3d printer.

Uh, excuse me a moment...

Right, as I was saying, I do have a 3d printer.

So let's make it squirt out some plastic.

So why did I make these spacers hexagonal? Well the answer is simple: hexagons are bestagons.

Anyway, I'll trim away the brim and slide them down over the standoffs.

And then the second DAC board snaps into place without any danger of contacting the first.

I do still need to get a second pair of SMC to BNC cables but I can get to that whenever I feel like it. In the meantime, I'm calling this upgrade a success!

SK-88 Or Die

So I was messing around with my Roland SK-88 Pro this afternoon and noticed that a few of the buttons weren't as responsive as I might have liked them to be. This is really quite a common problem for electronics of this vintage, as the tact switches will oxidize over time causing their contact resistance to rise from a few scant milliohms to dozens or even hundreds of ohms.

Thankfully the fix is pretty simple: just unsolder the old ones and solder in some new ones. I'd picked up a pretty decent sized stash of compatible tact switches after replacing the ones on my MC-303, so there was nothing stopping me but time and motivation, and I found an ample supply of both this evening.

The original tact switches were a slightly different variety this time, having a round case instead of a square one, but the lead spacing (5mm) and height (5mm) was still the same and there was plenty of room on the PCB to fit the square ones.

The process went very smoothly and I'm happy to report that the new switches work flawlessly.

Lead, Free Solder

The synthesizer stack grows ever taller, this time with the addition of a Roland XV-5050 rack-mount module. It's much smaller than a synth with an attached keyboard as it's designed to be used with a separate external MIDI keyboard or sequencer, which I'll elaborate on in a future blog post.

For now, though, I need to get it to actually work as I did, of course, purchase it with those four magic words "For Parts Or Repair".

This time the culprit was lead-free solder leading to a manufacturing defect where a number of the pins on the DSP that runs all the audio weren't properly connected to the PCB. Thankfully I just got a fancy new soldering iron so this gave me a great excuse to take it for a spin.

The end result is a working module full of sounds that I will have a wonderful time exploring.

Melting Metal

Continuing with the theme of liquifying things that are usually solid, I decided that it's finally time to upgrade my soldering iron. There wasn't really anything wrong with my old iron, save for the fact that it was a fixed-wattage style that took a good 5 minutes to heat up when first turned on. Technology has apparently advanced somewhat in the last 30 years (who knew?) and modern soldering irons now have full power control with a temperature probe in the tip, so they can heat up to 400°c in a matter of seconds with a 200w heater cartridge, then scale back the power to maintain exactly that temperature, give or take, depending on how well the PID loop is tuned.

And I guess they also want me to get high on the solder fumes.

And then take a little nap on the hibernation seat afterwards.

Alright, it's shiny and new, so let's enjoy the peel.

Oh yeah, that's the good stuff. And let's not forget the lower display too, just grab the little tape tag and...

Oh, hmm. That's not right. Well, a little digging around the edge with a craft knife gets it started just as well.

I guess the QC doesn't include verifying the quality of the film peel.

So as I mentioned, this style of soldering station uses a removable cartridge.

And since I tend to run into a variety of soldering tasks, I opted for the one with two different handles that take larger and smaller tips.

The larger is T245 and the smaller is T210. The larger one is nice when I need to dump a lot of heat into a part to get the solder to flow properly, while the smaller one will come in handy when working in tight quarters.

The base station has a fancy colour display and really likes to beep at you at every possible occasion. I guess that's going to take a bit of getting used to, but luckily there's a volume control I can turn right down.

As for my old soldering iron, I guess it's time to find it a new home.

Perhaps the next owner will actually get around to using some of the spare tips.

I guess only time will tell.

Welding Spots

Continuing with the theme of sheet metal tools, I decided to add a spot welder to my arsenal.

Admittedly the motivation here is partly "they're really cheap" but I also have a project coming up where being able to weld together pieces of sheet metal will be preferable to riveting them in some spots. But more on that in a later blog post, for now let's get this thing out of the box and test it out.

Yup, looks like a spot welder. Interestingly the instructions seem to imply that the time required for a weld is at least partially dependent on operator skill, which is an interesting take.

Since this is a 240v welder they apparently decided that there's too many different options for 240v plugs so they just ship it without one. So, $20 added to the final price to make up for that, I guess.

Well no worries, on it goes.

Now I can just plug it into the 240v outlet in my car hole which is right over... wait a minute.

Just kidding, I actually did this on purpose. My TIG welder also uses a 6-50p, and I have an adapter that goes to 10-30p.

I could have bought the 10-30p plug for this, but I eventually want to put in a proper 50a 6-50r receptacle, so swapping the plug end out again later would just end up being a waste.

Of course this spot welder only requires 16a so all of this is overkill, but it's much more convenient than trying to figure out how to power a 120v spot welder since most of those require a 40a 120v circuit, and who even has those?

Anyway, time to stick some metal together, so we'll grab some scraps of 26ga galvanized.

Spot welding is really nice for galvanized since it doesn't boil off nearly as much of the zinc as other welding processes, so you don't have to strip off the plating or take extreme measures to avoid inhaling the fumes.

Alright, let's give this a zap.

Ok, that was too much zap, I left a little smudge of the electrodes in the weld. I guess on the bright side I didn't blow a hole straight through, so that's nice.

I think I got the timing worked out on the last weld. I really does only require just a tiny tickle on the switch to produce a solid weld on this gauge metal, despite the galvanization which can sometimes require a bit of extra energy to zap through.

And it is properly stuck together, I pried the sheets apart here and the metal just bent right at the weld nugget.

So that's another capability unlocked I guess!

Just A Little Nibble

So I have a project coming up where I need to fit something into a square hole. Getting the thing in the hole isn't the hard part, though, it's making the hole in the first place in a piece of sheet metal.

You see, if you want to make a small round hole, you can use a step drill bit. If you want to make a large square hole, you can use shears. But a small square hole? That requires a different approach.

I have chosen the approach of using a nibbler.

The way this works is, as its name might suggest, by nibbling its way through the metal, using this square edged punch thats drawn down into the face of the tool.

So let's give it a test run on a small piece of scrap, just a bit of 26ga galvanized left over from a previous project. The first step is to drill a 3/8" hole so that the die of the nibbler can fit through.

And yes, installing this toggle switch in a piece of sheet metal is the actual task I'll be aiming to do later. It requires a 1/2" by 3/4" rectangular hole, which I scribe out on some blue sharpie.

The scrap itself isn't perfectly square, so ignore that it looks a little wonky on the top edge.

Anyway, let's give it a nibble.

Well that was refreshingly easy. The nibbler went through it just like butter.

Also pro tip: if you've never used one of these before you might think that the tool should be inserted from the top, but it is way, way easier to guide the cut if you insert it from the bottom, so try to do that whenever possible.

After making a full lap, the hole is pretty close to the marks, but I did miss them here and there by just a smidge.

Rather than try to shave off the last little bits with the nibbler, I'll instead use some files to take the cut to the line. It'll also give me a chance to deburr the hole, which can be a little sharp on the backside.

And a test fit shows that the switch snaps right in.

And everything looks good from the back too.

Well, I'll call that a success.

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.