Hi, it's time for a retro product tear down. I've got a Yamaha PSR 8 keyboard from the 1980s coincidentally that we're going to take a look at. It's actually uh, got a bit of a fault in it with the volume control and I thought we'd open it up. take a look inside and see if we can fix it.

Let's go now. The problem with it is that it is stuck on maximum volume. There's a master volume control here and it's stuck. regardless of what I do to it.

it's that's minimum and that's Max It's exactly the same. So something dodgy with the master volume control. Well know what we say here on the Eev blog. Don't turn it on.

Take it apart now. This is a 1987 vintage good year that so it puts it about 25 years old. and it was, uh, the one of the first series of keyboards that used the uh awm uh sampling control system. So let's go ahead and take this thing apart now.

I Expect a whole bunch of through hole uh components I expect I expect primarily through hole technology of course being about 87, but we'll see now. I'm assuming that these screws are going to take it apart. Looks pretty basic to me. This one's actually powered from um either uh I think it was at 6 or eight D cels um or 12 Vols DC 9 to 12 Vols DC and uh I believe it's a pretty darn good um sampling keyboard I I'm not really a muser I have Well, I'm definitely not a muse so I got no idea about how to drive these things and it does seem very complicated to actually drive.

and there's no, um, uh, there's no indicators on the front to show you what mode you're in and it is rather unusual to actually try and use it. So I've got the manual, but jeez, doesn't help all that much. So did I forget one, Possibly forget two? No, there we go. All right.

So I expect that screws will fall out for a second Tus. but uh yeah. One of the weird things is is that it doesn't have any indicators. It tells you the orchestra's on, but it doesn't.

It doesn't tell you what mode you're in or anything and there's all sorts of sequences and weird stuff with it. And I don't know. musos are probably laughing at you're right about now, but let's see, it's opening somehow. Maybe I do have to actually take the bottom off? There we go.

Sweet. Tada There it is. Bit of old smell, old school electronic smell. I Love it and no real surprises there at all.

It is, uh, through hole. It's got the oldfashioned, um, oldfashioned connector ribbon uh, cables like that just directly soldered onto the board. There's the keypad array up the top, two big speakers in it, and a whole bunch of just, uh through hole technology boards. And the board I'm after is uh I believe.

probably tucked up under here so we'll have to try and take this board out and see what's under it. and that's a typically old school kind of uh PCB Very typical of the 1980s bit of bit of residue down in there I'm not sure what. not sure what that is. it's uh, bit of white white residue on the board.

It's probably nothing but uh, it looks pretty clean and uh, and check that out, they've just solded the ground wire for the uh, uh for the keypad. uh, back in here, all the metal work uh for the keypad is uh, connected, presumably through to um, one of the uh, analog or system grounds on there. and uh, so all of that mechanical stuff is earthed and there's a few ribbon cables connecting the other boards and well, it's um, it. It is very sort of manual, uh, labor intensive.

Uh, kind of stuff to have to, you know, solder on the individual they wave solded. uh, the board. Obviously, you can actually see that if we have a look at the uh, construction of the board here, you can see that, um, it's it's not hand, Of course, it's all wave solder. The pins are pushed over like that.

very, uh, typical of that sort of uh era and uh, they you. But they've got a hand solder these ribbon cables on and you know they've gone to a bit of trouble to use to use some connectors elsewhere. But I don't know these would have been very high value uh products back then. very high margin uh products.

So I probably would have expected some connectors there instead of just the hand soldering of the ribbon connectors. And if you look at the back of the key mechanism there, that's I'm hitting the key and it's got like a soft uh, you know it's like a felt is that red felt material there is designed so when the key flings back, it doesn't actually make a sound. Bit of attention to detail there so it doesn't go clang. You know when it when it hits the plastic or metal, uh back in.

it gives it sort of a nice feel when it Springs back I Like it now. this board's rather annoying actually. I've undone all the screws here which didn't actually hold the board in place, but they held this back bracket in place and it looks like I may even have to desolder this ribbon cable cuz it doesn't give me me enough slack to actually get the thing out past. sort of that.

That's about the best I can do, but we should be able to see under there. So there's the underside of the board that you can see in there. and uh, all lots of Elros as you'd expect. and uh, and I think the volume control I'm after is actually on this little board embedded under there.

So to get to that, I'm probably going to have desolder this board. Bummer. I think I know what that white stuff might be I think it might be uh burum. uh, heat syn compound.

Because if you take a look under the bottom of the board here and let's have a look, there's quite a few devices heat sinks under there that uh, so you can see that the heat sink compound is just smeared all over the side of the heat sink. Brilliant. Better go wash my hands. Got it There you go.

Managed to get it out without having to desolder that. And there's my volume control pot and my onoff switch on its own little board. Like the system design in this thing, you know, like why put those two things on a different board like that and have ribbon cables coming over it? You know, from a system design point of view, a lot of this sort of doesn't make sense. but oh well.

who am I to argue? Anyway, we have good access to that pot now we can measure it. I'm getting no response from that pot at all. What? cleaning solvent in there probably not the best thing to do and I'll give it a, give it a few wipes and see what happens. No, it looks like that slider pot is dead and I've got to replace it.

And well, that's very unsurprising because these things one of the first things that goes in these mixing consoles and other uh keyboards. Very common for these pots to eventually D and wear out. and that's what looks like has happened here. So I either have to find a direct replacement for it or uh, some sort of um, or some sort of actually modify it um, somehow and include some sort of other pot in there.

And of course, this is all single sided board construction back then easier, lower the cost. Very typical of uh, stuff of this era and consumer goods like this. Look at all the links in there. a whole bunch of links.

Uh, no surprises at all. They got four 58 opamps which are audio class opamps scattered all over the place. single in line, uh, packages you don't see anymore. Um, they're very rare these days.

There's a relay up here, and uh, there's not too much else. There's this heat sink which is on the back of the Uh IC down there. that's um, probably. Well, obviously some sort of Uh amp IC or something like that.

and there's a looks probably a voltage regulator down the bottom here. But apart from that, that looks like sort of the main um IO main like a power supply and uh IO board because it's got the analog uh inputs and outputs on the back here. Wow, This really isn't a very serviceable, friendly design at all. It's almost as if they build it up from the base.

you put in the base boards right under here, and then the ribbon cables come out. and then you put in this module and then you solder them on like this as the last step. and then you put this one in and sort of, you know, like a step-by-step procedure and to undo it. Um, it looks like you've got to undo unsold of these ribbon cables to really get these out.

I mean I can get these These are on. These are on connectors going into the keyboard here, but jeez, you know there you go. I Finally managed to fold it out here and you can actually do that. Uh, these are actually um, directly solded onto the board.

They haven't got actually connectors on both ends. they've got connectors on one end which connects to this board up here. But apart from that, it's actually it looks like it's a connector down in there, but it's not. And there you go, a whole bunch of uh, dip packages and once again, this is a double-sided board.

but uh, it does actually use links they haven't bothered to put through hole. Um, it looks like it's non uh, through hole plated so, but it's double-sided to get the ground plane on the top. Really rather remarkable. and I haven't seen uh construction like this for a long time.

You can see that uh, like one end of that that link there is actually soldered through to be used as the through hole to join the top to the bottom. But apart from that, there's the uh, you know, there's there's the links for singles sided if they use a through PL Board Of course they could have not bothered putting the links in and done that. So really, they've um, tried to save some cost there. They've decided that they need the double-sided board for all the shielding on it.

Fair enough. and uh, But then they've decided, Well, we're not going to pay for uh through Hall boards. We're just going to make it. We'll just solder the links where we need to.

Brilliant and I Love these links here and here. They've decided that they need to link from there to there, but they couldn't be bothered moving the capacitors over or they didn't have room with the tracers. So they just instead of putting a straight link, they decided to put just an insulated wire link over the top like that. Oh, it is so old school and bodgy, it's just it's hilarious.

There's an old package you don't see much these days. The old, uh, staggered, uh deal package like that with the staggered pins to, uh, give you um, because it was a very small uh pin pitch smaller than your standard 0.1 in. They would, uh, stagger them like that so you could have large uh, solder pads um on your pins. You can still get the advantage of that, but there you go.

It's a Yamaha branded chip and there's quite a few Yamaha branded chips on here and here. We've got an An Oki brand 82c 55 I recognize that that's the old Pia or a programmable interface uh chip. So I expect the Uh processor is most likely this uh Yamaha branded device up here and that's got a number on it of uh X it's actually a Yamaha brand made in Japan and it's XD 285 A0 3B 1 y 0d 52p so I'm it's an 85 I don't actually know what that is I can't make heads or tails of that part number off the top my head I Can only presume that's some sort of 800c, 88 or 8086, Uh compatible micro or something like that. go figure.

And over on this end of the board we have a super cap There you go, plus another couple of Uh 458 uh audio all pamps up there and that's um, and a whole bunch of other Yamaha branded uh Yamaha branded Parts on there. So it would have some sort of uh, you know, one of the uh waveform you know the custom Um sampler or something like that would be in there I don't know something like that and uh, presumably uh, some of the um, all the sample uh stuff would be in the memories down here now. One interesting in device or actually they've got two of them is the Uh YN 312 3012 and that's a Yamaha um floating Point digital to analog converter Yes You heard that right floating point. It's got a 10 digigit uh, Mantisa and a three digigit exponent 16bit Dynamic uh range digital to analog converter chip.

Brilliant. And what we've got is a big metal shield going through here and that's obviously going to all the switches on the back. They got a couple of ribbon cables going down in here and if we peel that back, we can don't have to undo it. It goes to uh, some of the switchboards and the various other switchboards on the front there, so that's not very exciting I don't think I'm going to bother to actually, uh, take that off at all.

really. So, um, that's about it. It's not terribly exciting this thing. Overall, this is the main board.

They've got the analog, uh, more of the analog IO over here, and they've got a midi inout board down here and and the keys up here. it's all terribly unexciting. Now, This is rather curious: I've taken the uh back of the keyboard off here and it looks to be your traditional um, soft contact uh switch but I believe it's actually a uh, variable resistance uh, or what they call a velocity uh keyboard because apparently how much pressure you put on there, it moves. This particular thing which actually applies more pressure onto these points here and I think it does actually change resistance with the pressure and you can see the Matrix arrang they've got cuz there's not many connections going to this uh keyboard.

There's only a couple of you know for what is it, 68 key keyboard or something. There's not many cables actually going over to this. so they got a multiplexed arrangement with uh dodes on the top here and that um, somehow that allows them to sample all of the keys and actually get the uh displacement of each key. It's rather neat, and if you actually take the rubber strip out like this, you can see each individual key popping up like that.

and they actually have three different prongs on there of slightly different heights. it's all not even so. it's as you put it down. it puts pressure in a different place on this strip.

It's rather neat. You should be able to see that fairly clearly there. They're sort of like they're not flat, they're in odd shape, and they're slightly different height and curved. Rather remarkable.

So if anyone actually knows how that mechanism exactly works with the rubber strip, I Mean you know it's not sensing the key? I'm sure I wonder if um I'm well, I'd be fairly confident they don't do something like this these days. Maybe I I would sense that each key would have individual uh sensing perhaps these days and they would do it differently. but this rubber strip is rather rather remarkable I like it. You can also clearly see that's it's broken into uh, equal segments like that.

so there's a break in the conductive strip at that point to separate uh, individual groups of keys or something like that. In case you're wondering, what that actually measures right next to each other on a key is around about a K Well, I don't really like my chances of actually getting one of these, especially in any reasonable amount of time. and I've got Sean screaming to get his keyboard back. So what I think I'll do is I'll just uh hack in a uh 10K um, just a a regular uh 10K log pot because this is uh 10K a and a signifies log.

So um I've got a 10K log pot here and I plan on just uh I think in the back here of the case, I'll just drill a hole in there off to the side and uh, run some ribbon cable over to the board over here and that should do fairly well. I'm not too worried about any noise pickup or anything like that because uh, this is just for playing around with really not for serious music generation. so I'll give that a go. All right, let's give that.

Got to try first and see what happens I heard something switch on yeah I can hear can hear noise in the speaker goes down when I hook the pot up. Yep, let's try key. that's minimum. Beautiful.

Wimer And there's some hum there that seems to remain regardless of where I put that wire. So obviously uh I don't know if that was there before um I don't actually recall or whether or not whether that's uh, normal, whether it's due to the uh ribbon cable going to there. But really, it's not a big deal. so I'm pretty happy with that.

Going to put it back together all right. Time to give it a try. We're on. It's slow.

excellent.