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.