Flashing Floppies

So I installed a Gotek on my Roland S-750. It worked, but it didn't automatically boot the system image when powering on. I had to select the image and then it would boot, which is peculiar.

I spent a lot of time tracking this down. I made extra sure that the flashfloppy config was absolutely correct and pointing to the right image file. I even copied the exact same config from my Roland S-760 that was working correctly and booting automatically. But no dice.

What eventually ended up working was setting pin34 = nchg in the FF.CFG file, though I'm not entirely sure why. In the schematics, it's quite clear that pin34 is active-low, and so "nchg" should be correct.

Or, well, I suppose "D_CANGE" is supposed to be active low. The overbar is clearly visible, at least.

But what gets me is that it's always supposed to be active-low, and I don't really understand why flashfloppy very clearly sets the pin to active high for the IBMPC mode.

This is very peculiar. I'm glad it works, I guess, but it feels unsatisfying that this contradiction doesn't really make sense.

It's All About Control

As mentioned in my previous S-750 blog post, my unit is reading a ghost-mouse on the EXT CTRL port, which results in a phantom cursor that slides down to the bottom-right of the screen at all times, disrupting the UI control. This is due to IC14 on the mainboard failing, and while I don't yet have a fix for that IC, I can at least try to work around it.

First off, the simple test: does bypassing the blown fusible resistor help?

Well, it would be nice, but no it does not. It still detects a phantom mouse and will not speak to the RC-100. So, it's time to get drastic. Let's have a look at the backside of the connector.

It's a bit grimy with flux from when the board was put together back around 1991, but other than that nothing looks too amiss here. I did see what looked like a blob of conductive something that might have been shorting pin 8 to ground.

But cleaning it off, as I expected, did not yield any improvement.

So the drastic step I'm going to take here is to completely disable this port. I'm doing this by shorting out pins 1, 2, 3 and 4 to ground. These are the pins used by the MSX mouse to report its movement, and by shorting them to ground rather than leaving them high, the movement will be reported as 0x0,0x0 instead of 0xF,0xF. We'll still end up with a mouse cursor, but it won't move, and thus won't interfere with the button-based navigation.

It's not the most beautiful solder job, but it'll do.

While I'm in here I'll also pull the blown fusible resistor, since it's not doing anything at all useful.

And then leave a note for whoever opens this next wondering why the EXT CTRL port isn't working and half the pins are shorted to ground.

Also while we're here, since this is now in a usable state, let's get rid of the floppy drive.

I do actually have the physical boot floppy for this, which is nice, but I'd rather not have to rely on a 35 year old mechanical drive. So in goes a Gotek.

Conveniently the set of thumbdrives I got to use with the Goteks was a 3-pack, so I only needed the floppy emulator itself.

Next up, the feet need some love. The front two are in good shape, but the rear two have exited the chat.

A little heat and scraping gets the remains of the tape off.

And after cleaning the remaining adhesive with some alcohol, the new feet go right on.

Weirdly this set of feet came in a set of 18, which is very much not divisible by 4, so I'm glad I found a use for the remaining two.

On the good news front, the video-out works, and gives a much better view of what's going on than the built-in front panel LCD.

The composite-out circuit is a bit primitive, though, and only displays a B&W image. It looks a bit fancier in colour, like when I hook up to my S-760.

Though you do only get 8 colours, since the display has only 1 bit each for red, green and blue.

183 Cereal Boxtops

There's just something about the aesthetic of the Boss Dr Rhythm DR-110 that makes it look like something you'd get by trading in an absurd number of cereal box UPCs. The sounds it produces are, from right to left: Raise the Roof, Umbrella, UFO, Umbrella Reflecting Off A Pool, Cat Food, Cranberry Sauce, and Free Public Wi-Fi.

I picked up this classic Roland analog drum machine from Japan because I had bought one (1) memory card for my D-70 and it felt silly to ship that by itself without combining it with something else. Of course by the time it arrived at the forwarding warehouse I'd also bought another rack effects unit and two more memory cards so it would have been fine to just ship those items in a bundle but let's not think too hard about that. The important part is that it was cheap.

And cheap for a reason, of course. The display was suffering from the classic "vinegar syndrome" where the adhesive for the reflective polarizer starts to degrade over time.

This is fine, though. Polarizer film is pretty cheap and easy to apply. Famous last words? Stay tuned, I guess.

But the polarizer degrading isn't the only issue these units tend to face. The other is on the back side.

Why yes, that is a curious stain next to the battery compartment. Very observant of you. Let's have a look inside to see what caused it.

Yup, that would be the usual battery schmoo. Interestingly, despite having more schmoo on them, the contacts on the left that go to the PCB are actually in better condition than the ones on the right that just bridge the batteries together.

Well, it's a good thing that this has a DC input jack.

Speaking of things going in, let's go in ourselves and see how things look inside.

The PCB contact side is looking pretty clean. The schmoo has corroded the traces a little on the main PCB, but very little of it dripped onto the front panel PCB below it.

There was quite a bit more drippage on this side, however, and at least one rivet via there looks like it's unlikely to be conductive anymore.

Well, it's time for the battery-schmoo antidote: plain old white vinegar.

The battery contact is cleaning up pretty quickly, though it's mostly pointless as part of the tab on one side has long since broken off and disappeared.

The battery contact on the main PCB is getting nice and fizzy though, the vinegar is doing a good job here.

Pulling things further apart, we can see the other side of that via on the front panel board.

And yeah, safe to say this isn't going to be very conductive anymore.

Speaking of not conductive, those PCB pads that the carbon pills are supposed to press against are looking a bit grimy. Let's clean them off.

A pencil eraser is the secret weapon here. These contacts are gold plated so they should clean up pretty easily.

And yup, that took off some grime.

Back in vinegar-land, the battery contact is now schmoo-free, for what it's worth.

The contact on the left is supposed to have a piece that folds back down over the front to make contact with the negative end of an AA battery, but as I mentioned, it's long gone. Well, at least it's clean now.

Speaking of clean, the schmoo corroded the surface of some traces around the battery contacts, but somewhat surprisingly none of them are actually broken.

It took off some of the solder mask, but that's not a big deal. Also in case  you're wondering the white stuff is just the flux on the board that was left there during manufacturing. I had used some alcohol to clean off the bottom section of the PCB here and the partially removed flux tends to turn pasty white when you do that.

Anyway, there's nothing really to fix on this board, so let's have a look at the front panel board.

And yes, up close this via is looking pretty dire. Scraping back the solder mask reveals a pretty obvious missing section of trace.

On the top side, the same via has another missing section of trace next to it, so it'll need to be repaired on both sides.

So it's magnet wire to the rescue.

And then patch things up with a fresh coat of solder mask.

There were a few other vias around here that had lost their conductivity but I'll save you the excruciating detail on those. It's just more of the same all over again.

So, before we put things back together let's actually see if this thing works.

Well that's an encouraging sign. I don't have the new polarizer film yet but it should be here in about a week or so. For now, we'll just have to deal with the ugliness.

Anyway, with everything back together things are looking much cleaner, and the unit actually works. The buttons all function, the sounds all sound like sound, and the pots aren't exceptionally scratchy.

And just as a reminder, I'll leave you with this photo of the back.

They wrote that there for a reason.

Seven Fiddy

I've been on the lookout for a certain piece of hardware for a little while, and just recently a good deal came up on eBay, so I jumped at it.

This here is the Roland S-750. It's a much older rack sampler than the Roland S-760 that I purchased previously.

And it is a chonky boi. It's 3u tall instead of 1u and a bit deeper than the S-760. What's somewhat amusing is that the boards inside don't really take up all that much more actual space than what would fit in a 1u case, but whatever, it is what it is.

Why did I want an S-750? Well I kind of didn't, actually. I wanted what it came with, which is this.

Wait, no, that's just a regular IEC power cord. I mean this.

This is the RC-100 remote controller, and it's actually worth more than I paid for the whole bundle together. So I essentially got a discounted RC-100 and a free S-750, which is kinda cool.

The RC-100 works with a number of Roland samplers, and in particular it works with the S-760, thus why I was interested in picking one up.

Anyway, fun will be had with the RC-100, but first let's see what we can do with the S-750. Inside we can see that it lacks the wave memory expansion, which is also something I'll be tinkering with later. It slots into the two grey connectors up at the top of the board.

But first, the volume knobs were looking a little misaligned and were binding somewhat, so let's see about fixing that.

The diagnosis of this issue is at least pretty simple.

This metal bracket is not supposed to be shaped like this. Let's fix that real quick.

And that's much better. Not perfectly straight, but it'll do. Back in the unit, things are looking much more aligned.

Though I do need to deal with one of the volume knobs, which managed to separate into two pieces while I was trying to pull it off the shaft.

A bit of not-so-super glue does the job just fine.

And the knobs are looking much better now.

So let's see what the RC-100 does. Just plug it in and hold the right buttons on the front panel to select it.

Except hmm, no dice. It's not powering on. Let's have a look at the jack board to see if it yields any clues.

It's the board on the right, there. Pulling it out we can see the problem pretty easily.

R35, a fusible resistor, has fused. This is not really a surprise given that it's on the +5v rail which supplies this port with power.

And as you can well imagine, with these male pins sticking out of the front of the unit, it's only a matter of time before something conductive comes in contact with them and lets all the magic smoke out of the fuse.

So a new pack of fuses is on the way, but in the meantime there's another problem: the sampler keeps auto-detecting a mouse, and the UI is scrolling uncontrollably when nothing is connected to this port.

After doing a fair bit of diagnosis, it looks like IC14 on the mainboard has fried. It's reading a very clean logic-high on the unconnected port as a logic-maybe, and interpreting that as (junk) data from a nonexistent mouse.

This is unfortunately a Roland-proprietary ASIC, and so no direct replacement is available unless I can find one to salvage from a parts unit. The other option would be to reverse engineer the ROM and OS to determine how it talks to this chip and then replace it with an FPGA. The chip doesn't do any particularly complicated tasks, it mostly just does the front panel matrix scanning, drives the LEDs, and acts as an IO expander.

Anyway, that project, assuming it ever happens, is pretty far down the to-do list so we'll see if I ever get around to it.

Oh and just in case you're wondering, the RC-100 works perfectly with my S-760.