When we last left off with the Rat Shack Synth, it was making noise but not very well. The tone was drifting upwards on the main oscillators and oscillator 1 wasn't tracking the keyboard properly.
But thankfully every problem has a solution, and after a bit of head scratching I managed to get everything working perfectly.
This right here is a Yamaha Reface DX. It's modelled after their classic line of Digital FM synths from the 80s and 90s, with the DX7 being perhaps the most famous and widely used synth.
This one has a problem, though. Some of the front panel switches don't work, and some of the LEDs don't light up.
For example, here's the LED behind the FREQ button lighting up as it should:
And here's the LED behind the LEVEL button doing a whole lot of nothing:
Oh and also it doesn't make any sound. I guess that's important too.
Now one of the problems with these compact synths is that because of their small size, people often tend to treat them like those old toy synths, even though, well...
But thankfully I didn't have to pay $500 for this one. Anyway, let's crack it open and see what's inside.
And interestingly there's more in here than I thought there might be. These days you can run a synth like this on a board the size of your thumbnail (not the chip, but the whole board) but I guess the Yamaha engineers decided to fill the space available to them. No harm done I suppose.
So over here on the left side is the chip that drives the switch and LED matrix.
If we probe one of the matrix lines with the scope, we can see it scanning.
But if we probe another line next to it, we see something that looks almost like a flat line...
However, if we bring up the vertical scale a bit.
We can see that it's still trying to strobe the lines, but it's lost its pull-down resistor.
Now I could dig into this board and try to figure out which resistor is faulty, or trace down a broken via, but I really don't feel like it when replacement mainboards are still readily available.
Though at $150 they're not especially cheap, but given the bargain I got on the synth I'm still coming in under budget.
Now to get to the mainboard we have to remove the keys.
And the keybed PCB.
And then to get the mainboard out we of course need a different size screwdriver.
But once we've got those screws removed, the mainboard just lifts right out.
And then the new mainboard goes in, after we've removed the curious bits of kapton tape that were stuck to each connector.
And we can verify that the switches are working and the previously "dead" LEDs have come back to life.
But the synth still isn't making noise, curiously, so let's check the volume slider.
If we measure the resistance on the wiper for the octave slider next to it, we get a reasonable reading:
But unfortunately the volume slider is being rather unreasonable.
And after spraying it with a little contact cleaner...
It's somehow still not working. Lovely.
Just to test things out, let's try jumpering the volume slider with a fixed resistance.
And if we test the resistance now, we see a much different result.
But unfortunately the synth still doesn't make noise. Because I put the resistor on the wrong pin, it should have been like this.
And now the synth makes sound. Good. So we can order up a volume pot, and let's just go ahead and replace the octave pot too since it was reading a bit funny on one end.
We just have to pull out this front panel sub-board.
And do a bit of desoldering. Using a hot air gun can really help with larger mechanical solder joints like these two tabs in the middle.
And with a little magical slurp from my solder sucker, both pots come out easily.
Goodbye old slider pots, you left us too soon.
Then the new pots get soldered in.
And all that's left to do is reassemble.
But there's still some finishing touches left.
Like replacing the missing rubber foot.
And getting rid of the Alkaline batteries before they leak and destroy everything.
And with all that done, we're back in business.
And ready to make some sweet 80s synth-pop!
So there's this piece of trim on the side of my roof that really could use some repainting.
The trouble is that it's behind this minefield here.
These are fiberglass roof panels. Seriously degraded fiberglass roof panels.
Basically if you touch this side, you die the itchy fiberglass death.
They didn't originally look this ugly, though, as evidenced by the part that was shaded under the overhang.
But that doesn't really help me much, so off they go.
I'm not sure if the panels were originally white and yellowed over time or if they were a yellow-cream colour from the start. The house was yellow when this awning was installed so the latter is certainly possible.
It was also stuck on with some weird yellow caulking where it met with the wall, which is a little pointless given that it's under an overhang so it's not like any water was ever going to get up there. At least it matched the old paint.
Speaking of colours, green was the trim colour when the house was yellow, and apparently they never bothered to repaint the awning frame. And, furthermore, never bothered to properly prime the aluminum so the paint would stick.
But the good news is I now have unimpeded access to the trim that needed painting, so I can start with a little bit of wire brushing to knock the loose paint off of it, as well as off of the awning frame.
And then a little love from the belt sander to level things out.
And finally we can get to the paint.
I used a rustoleum aluminum primer on the frame so we'll see how that works I guess. I'm pretty confident that the exterior white latex paint will stick just fine to the trim though, which is looking pretty fine.
Finally, a new set of roof panels goes on to replace those scrungy old ones.
These are a polycarbonate roof panel in the "white opal" colour, which is basically just translucent white. The good news at least is that there's no fiberglass in them to eventually be eroded to the surface, and they promise to be UV-protected though we'll see how that holds up because there's an awful lot of UV around here.
Except I'm supposed to be walking on concrete.
This here is a section of the concrete walkway beside my house, right in front of my brand new and expertly installed car hole door.
I'm really not sure why it's a separate piece, although it's possible that the landing for the car hole door was poured first, and the concrete walkway was added afterwards. The two different slabs of concrete do look slightly different.
Anyway, it's unfortunately sitting at this jaunty angle, which just happens to be the perfect slope for twisting unsuspecting ankles.
Now I had initially considered the idea that I might just skim over the top of this with some fresh concrete, but that would require doing some form work to keep the edges nice and neat, and then I'd have to finish the new concrete surface to make it look pretty, and so on. Instead, I decided to try just pulling this slab out so I could backfill underneath it to bring it back up to level.
So step one: dig out the pea gravel around it.
Well, not just the pea gravel, but also the fossilized layer of dryer lint and other debris and detritus.
There's even some full on dryer sheets in there, which really makes me wonder how this house didn't burn down decades ago from a dryer lint fire.
Oh, and there was also this peculiar D6.
Apparently it's from backgammon, which surged to a peak of recent popularity in the mid 1960s through the 1970s before fading back into relative obscurity over the course of the 1980s.
But enough about the recent history of backgammon, back to the task at hand. The slab in question is just barely small enough to be lifted out by hand, which is what I did next.
And this of course revealed the cause of the slumping: moles. It's no surprise that they've been digging under these sidewalk slabs, and for the most part to no ill effect. But this slab was small enough to be able to sink into the undercut over time, after which the moles no doubt would dig their tunnel a little bit deeper, and so on and so on.
So something tells me this might not be the last time I need to jack up this slab.
But before I worry about jacking up the slab sometime in the future, I need to get on with jacking up the slab in the present, so let's mix up some concrete.
I'm going with a sand-mix again since I only need an inch or two of depth here, and I have a bag of sand and a bag of cement left over from skimming the sidewalk on the other side of the house a while back.
Pro-tip: don't keep bags of cement laying around. Even in a dry climate they'll pick up moisture from the air and start to go off. Luckily I don't need any particular strength from this pour; I really only need it to be "fill that I don't need to worry about compacting" so this will still do the job just nicely.
I needed about 1/2 a cubic foot of concrete to bring the slab back up to roughly level, so I started with a gallon of water in my bucket and used my amazing paddle mixer in my rotary hammer to mix. This time I went with 3 scoops of sand for every 1 scoop of cement until I got a nice consistency, though it wasn't feeling as sticky as I wanted so I splashed in a bit more water at the end and added another scoop or two of cement.
Well it certainly looks the part. I sprayed down the dirt before dumping this mix in to keep it from sucking away all the moisture, then I spread it out and cut some peaks and valleys into it with my hoe.
This helps the concrete spread out evenly under the slab without trapping too many huge air pockets.
Then all I needed to do was tip the slab back into place.
And pack it with pea gravel to keep it from moving.
It's already pretty much fine to walk on right away, but I'll give it a good 24 hours to set up nice and stiff before putting too much weight on it. The good news is that I calculated the concrete volume pretty much spot on, so the slab is back up to basically level again.
Or at least as level as any of these slab sections are.
