Hi, it's Retro Computer time again, we're going back to the future. Tada It's the Cambridge Z88 notebook computer Z80 based of course. as you can tell from the title, this comes from the legendary CLI Sinclair out of the UK and he's developed several computers over the years famously the ZX spectrum and the Zx81. but this is the only one that came from the Cambridge company which he set up and this is 1987 vintage right Here it's A4 notebook size huh? Before they even called them notebooks and under a kilo.

it's a really neat little bit of Kit I Like it now I Thought we'd tear it down and as a bonus, this one doesn't work. So I Thought we'd have a shot at, uh, troubleshooting this thing. Possibly fix it. Let's give it a go.

Good on you. Clive And here it is. In all its Glory It's got one of these sort of of rubber, uh, membrane type. uh keypads.

I mean they're raised keys on there, but it feels very spongy and uh, rubbery. I Guess it was designed to be silent. You know? So you're using this thing out on the road. You're a road warrior.

Um, you know, back in the days when well, you know these things were uh, used a hell of a lot by uh journalists and things like that. especially the Tandy 100102 which I have torn down in a previous video which I'll link in here if you haven't seen it and uh, this. it's a really nice bit of Kit I'm not sure what the resolution of the screen is I haven't uh checked, but it's you know, it looks like it's 80 characters by eight lines or something. maybe.

Um, it's got all the uh, various shortcut keys I don't know why they bothered there really and uh, you know it's got some arrow keys. pretty basic keepad though index menu help, not much else. pretty boring. Um, on the side here, we've got a a DC input jack.

uh, contrast nothing on the top and on the side. Here it looks like we have a Serial Port RS 232 serial Port but that's pretty much um, all she wrote in terms of uh ports. although there is a connector under here, so let's have a look at that and looks like we have a card Edge connector there? um I'm not sure what. uh, that's designed for some sort of uh, expansion, uh, header connector.

One of the big selling points though of this thing were these Eom and memory packs. Now these Eom packs. They're uh, just like proton packs, except not as cool. Sorry Another 80s joke there.

Um, and yes, they are actually Eoms. Check it out. There's the Eom inside there standard dip package in there I'm sure with the Eom window now. now that one's a 32k Eom, so that would be you know, a standard 27c, 25c, 6 or something like that.

This one is a much bigger 128k Eom and you can see it in there. Much bigger die in there so you can actually UV erase these things. and uh, these were. so this actually contains an Eom programmer in it.

so it's got to generate the 12volt high voltage programming pulse presumably um to program these particular Eoms. But you could also plug memory into these these 128k Ram pack and you could expand this thing up to 4 Meg or something like that. It was actually quite. uh, a lot of memory for its time.

really. So um, this thing in terms of memory expansion was, uh, really. um, quite a significant machine. and it comes with 32k of ram built in.

but of course you can expand that with the pack it. uh. operating system in this thing as a custom one, it's called Oz Beauty and uh, it came with a, you know, a word processor and stuff like that called pipe Dream and uh, spreadsheet I believe. So there were some built-in apps just power the thing on and it ran from uh, four Ablea batteries for about 20 hours.

Brilliant. There's a nice little flip out thing here so it tilts it while you're using it on the desk there. Really quite neat and there's something you don't see every day. made in Scotland by SCI UK limited serial number 2,938 Hi to all my Scottish viewers.

So sorry I can't do a Scottish accent and if I could, it wouldn't be able to understand me cuz nobody can understand the Scottish accent can they? And damn it wouldn't You know it. It decided to work. This thing was not working before and I was hoping to do a troubleshooting video. What a bummer because I was even uh going to start out with the fact that when I plugged in the batteries I could hear, um, a very faint high pitched uh, you know, DC to DC converter noise in there.

So I was going to uh, you know, mention that uh, you know, start troubleshooting. Oh, you've got to use all your senses. You know your sense of sight, your sense of smell and your sense of hearing as well as touch. You know to see if anything gets hot things like that.

So um I thought I you know I heard something in there and I was going to start with that. What a bummer. a sorry it's just going to be a tear down video I think unless it's intermittent I don't know M can I uh oops hey I just got into Basic there. somehow.

there you go. I Just got into the Uh Z80 Basic Version 3 Copyright: RT Russell There you go, Who is RT Russell H There you go I just Googled it and it's Uh Richard Russell and his company RT Russell Uh was set up to supply the Uh Basic to the BBC Micro back in the early 80s. and uh, the same basic interpreter was also included in the Amstrad, N. Nc100 and other machines.

So there you go, Good on you. Rich. Now this thing. I Expect to find uh through hole technology.

Of course there might be some surface mount stuff. there'd be some surface mount stuff for like the LCD driver and uh, stuff like that I'm assuming because it was definitely 87 so Mount was around before then. but uh I expect to see some classic stuff. It'll smell like vintage Electronics 2 which will be fantastic.

and uh, got a whole bunch of Phillips screws here and this is based on the Z80a. CPU working at a who in 3.5 something? Mehz. So Abs Abol itely screaming along for the day, but you didn't need anything faster than that. Really? have I forgotten something? No.

Tada Oh, hang on, hang on, hang on. It's falling apart. Looks like this top just pops off. Oh there we go.

I forgot to take the batteries out. Oops. So there you go. It's uh, rather interesting in that uh, that front bezel just lifts off and there's the battery compartment.

Looks, there's an inductor down there. we'll have a look at. Look at that. There's the Uh D9 connector with a resistor soldered onto the shell as well.

Look at that. I Love that. Absolutely classic. And the Uh LCD Oh, there we go.

It's an Epson made in Japan and uh, that one is a, um, just like an 8bit parallel interface or something. so that will have a whole bunch of uh SMD drivers in there. but uh, that will come out later and hey, here we go. Tada There it is.

Yep, a mix of uh, basically mostly through hole. um through hole resistors through hole caps. just briefly go through the main board here. we've got uh, contrast pot over here.

We've got a reset switch right up in the corner there. DC input jack. Um, we've got a super cap there to hold the Uh charge when you replace the batteries because you don't want to lose everything if you got them inside your 128k RAM pack. I mean these are, uh, these aren't Dynamic Rams These are only srams so they don't need anything.

They can run off the sniff of an oily rag these things. And there's the main. uh s. There's the built-in 32k uh SRAM chip.

We've got our um, eom there, that's uh, system ROM I think it was 128k system ROM or something. It's got 2.2 written on it. version 2.2 presumably and uh, what's SKS not sure, but 1987 Cambridge Computer limited Uh, we got another chip over here. We'll have a look at that.

Here's the main uh, Z80 CPU that would be the Z80a. There's the Uh 3 8304 MHz Crystal and ah little pissant speaker there and looks like there's another little switch hidden inside there so you can sort of access it through that option compartment I wonder what that little, uh, sneaky switch there does? I Don't know, but there's a whole bunch of uh, T92 transistors all bent over here. Lovely standard uh, axial 5% carbon resistors. Oh man.

Beautiful. Oh classic doublesided board folks all through hole technology. Just love it. Looks like theyve got a 30 2 khz watch crystal there as well.

As you know, they got some some crusty old double-sided tape there sticking down that Crystal that used to be a very time oned uh method of uh, dodgy sticking down your Crystal just whack it on some double-sided tape. Who cares how long it lasts? And there's the Z80 CPU It's supposed to be a Z80a, but it only says Z80 on there. Anyway, it's 8722. So this one was manufactured well.

That chip was manufactured the 22nd week of 1987. So this one uh is because it's serial number 200000 and something. It is a very early unit. It's probably one of the first Uh runs.

In fact, it probably was the first Uh production run on the thing. So uh, looks like we got an inductor there for some sort of little switch mode I don't even know if it's A because I don't see a controller around there. There might be, you know, a couple of switching transistors or something I don't know. But so I'm not sure what that inductor is doing up there.

Uh, not entirely sure. But anyway. oh, hang on, it. just switched off.

It just switched off. Oh, I'm not sure if it did that because it's going to sleep or uh, because I touched something or or it's intermittent somehow. Well, I managed to get it going again by just uh, hitting this button here which looks like it's a power button cuz you hit it and it you know, but why it's recessed like that? Maybe it. Well no, it looks like there's you know, looks like it was actually a recessed hidden switch.

And by the way, this one down in here. If you hit this, it beeps and looks like it. It doesn't it? Well, it resets the thing and refreshes the screen. So all right.

I Figured it out. This is the soft reset switch down here and this one is the hard reset. By the looks of it, there you go. And because if you push this one up here, it'll actually tell you very quickly up there.

soft reset. So there you go and it tells you it's running. Oz I Like it. Brilliant.

Um, so it seems to work just fine. so let's have a look at some other stuff we've got in here. I mean all the T 92s, uh, transistors there bent over absolute uh Classics there? BC 558 and stuff like that. 48 and we've got an NEC uh, D what is it? d6503, Gf1, 168 there I have no idea what that one is.

Obviously some sort of uh glue logic to replace a couple of uh devices that you know that are used in a traditional Z80 architecture machine. But uh, yeah, look at all. the I mean they've got one resistor Network there one single inline resistor Network there. but everything else.

they got resistors everywhere and transistors everywhere. Very discret design. and uh, there's the super Cap. Of course, that's a 5.5 volt.

Uh, NEC 047 Farads There it is. and uh, that is about all she wrote. There's not much else. There's a variable resistor there.

Not sure what that one uh is doing, but yeah, there's a curiously, there's this bar along the uh along these expansion plugs here. so I'm not actually sure what that's used for. You know, it's like a stiffener or something like that. You know it's not really performing any sort of um, shielding function at all.

really. So um, probably some sort of stiffening bar just for that, just for holding that connector in place. But why it doesn't go all the way? extend all the way to the end. I Don't know.

and there's a there's a weird ass uh expansion connector for the cartridges and uh, you can. It looks like you can hot swap these things. It just sort of blanks the screen for a second and then pops back up. but I can't seem to access those.

Got no idea how to use these things, but there you go. Pretty old school and I've got manual wiring? Of course you know they've just solded that uh serial cable directly into the uh pins on the board there. Pretty dodgy. You know they've got that There's that resistor going through to the uh uh shield on the Um D9 connector.

Ah, dodgy as it's a very dodgy 80s construction here, you know, But this is what it was like back in the 80s. This is how they'd manufacture these things. so um, you know it's They sort of really haven't Hadn't perfected the mass manufacturing techniques that they have these days with the surface mount pick and place machines. Although you know we've got a perfectly good, you know, surface mount device there.

They didn't extend that anywhere else on the board. and if we flip the board over and have a look, it's uh, pretty, uh, conventional. Nothing going on there at all. No hacks, no mods except for this weird looking add-on Check this out.

I Don't think I've ever seen anything like that before. They've got this big copper strap going from this ground. Trace Over here near the B uh section down the bottom here and it's just jumping that all the way over to there. They got a plastic spacer which moves on the bottom of that and so it basically connects this big uh ground Trace over here all the way over to here and why they've done that? I Have no idea.

It's obviously not serving any useful shielding purpose, so they've It seems as though they've done it for layout reasons like they you know they routed the uh, the battery uh, ground Point down here and they went well, you know. I We have to somehow get this all the way over to here and well, we've only got a double-sided board don't have the luxury of a multi-layer board so we're going to have to jump the thing all the way across. And rather than putting your traditional uh link which you don't see any of here on on this unit, by the way, there's no wire links on this thing. um, theyve just used a big white copper strip I Don't know.

They don't need the current handling capability. So why they don't just didn't wire in just a, you know, a black mod wire or something like that. um I don't know. For some reason they decided on that weird oh I jumped to the conclusion that what? that was the ground but I measured it and it's not.

It's actually the battery positive and uh, it's and there it is. Of course it's obvious. look at the why the battery positives there and the negative of the battery is not until all the way over on this side of the board here so it's almost as if like they, um, maybe you know, needed some extra current cuz it does go out to one of these tracers out here for this expansion header. but jeez, you know why it's that huge and whyde just to jump over to here? I Don't know and how much does it draw during operation? Well, 60 odd milliamps just sitting there at the main index screen and they have actually two jumpers on the top.

Here, you can see these two black wires going from the negative terminal battery over here. one goes, one's terminated there at that point, and the other jumps all the way over right to the other side of the battery terminal right over here. So instead of routing those I Guess they ran out of routing room, they had to jump those all the way across. Oops! Now I was actually wrong on that clock frequency.

It's actually 9.83 4 mahz. So what I'm going to do is just probe the clock here and see what this thing's doing because uh, I suspect that it's not possibly not running all the time. Um, because these things like you know this to get, uh, its uh, 20 hours? uh, battery life? Uh, these things went into sleep a lot. So it might be waking up For example, when you press a key, so it might be sitting there waiting for a key press.

So let's probe the uh, Z80 processor down here. Um, Pin Six is the clock line for a Z80. A 40 pin dip Z80. So 1, 2, 3, 4, five, six, hello, Hello There we go.

and look at that. I'm at 2 Vols per division. so it's 246 so it's running practically directly from the battery voltage. so it looks like it's not 5V regulator in that and that looks continuous.

Uh, let's hey, no, hello there you go. Check that out. Aha, look at that. There's looks like there's a group of two bursts.

Oops, the thing just switched off on me. The screen's gone. so let me reset that. Ah, there we go.

and we're back. So there was no clock frequency when it was dead like that. So I'm not sure what's going on there, but anyway, where? Uh, 50 micros per division though. So 100, 200, 300, 400 microsc It goes for in two bursts there.

I'm not sure why it has that uh, Dead period in the middle of it, but uh, 400 odd micros seconds And then aha, there you go. It repeats. that repeats that every two divisions 10 milliseconds. So there you go.

Every 10 milliseconds, there's a 400 microc burst of clock. and uh, it's able to get away with that because, uh, it's obviously doing nothing. and if we actually ran a program, we would probably see that change. So I might try and run a basic program and or something and see what happens.

All right. I Got a very simple basic program there. It's just going to count up to a high number, print it on the screen, and keep doing that for a while. So let's run that and see what we get.

All right. So that's what we're currently getting. So let me just type in. Run Here! Oh, you can see that every time I press a key bang, it sort of extends that pulse out there.

So I'm going to press run and we should get a continuous clock. Yep, there we go. Fully continuous and our our thing's counting up. It's only to it's not even to 200 yet so it's uh, pretty slow this old sucker.

and I've turned on the hardware frequency counter here and it's 3.26 6 Odd megaherz. So there you go. It's obviously dividing that Crystal that 9 MHz Crystal by 3. but if you have a look at that, there is still a period in there where it blanks out even though it's continual.

I'll try and single shot capture that. There we go. Bingo We got something and we can zoom into that here and you notice there's a dead period there of 5 10, 15, 20. almost like around 24 microc seconds.

There's a dead period so it obviously, uh, needs to or is stopping the clock for some particular reason for 24 micros in there. Not sure why and look at this. This is what it was like in the 80s. This is how slow computers were in the 80s.

Check that out. Every cycle was sacred. Oh feel like whistling Money Python. So I'm sorry I wasn't able to bring you a troubleshooting video that I was uh, hoping for.

Maybe next time but we all like a good vintage retro computer. tear down and uh this one was an absolute classic I hope you liked it the Cambridge z88 ha Clive What a winner! Catch you next time.