Hi a while back I Got this really nice Tectronics triple 25 oscilloscope and I uh did some basic uh checks on it. Well, Fair reasonably comprehensive uh checks anyway and found that the vertical and the um horizontal, uh uh calibration was slightly out so got the service manual for it I Thought we'd do a bit of a tear down and uh, see if we can, uh, tweak this thing just a little bit to uh, bring it back into cow so let's go to take it apart. There's only a couple of uh Torx screws on the side here I don't think they're original. there's one missing so I'm not really sure what's going on there, but uh, you undo those screws and it should just slide off.

Um, that's how most Scopes work. So let's give it a go. and if you're going to put your scope uh, face down on the bench, just Beware of the controls and how far they protrude, usually they protrude uh, further than the screen like that, but uh, these ones on the old Tech Scopes are pretty darn robust, but just be aware that, uh, that can be an issue and there's a couple of little uh, catches on here like that and uh, you get those off and we should be able to slide that sucker off upside down. Taada.

There we go, and there you have it that's inside the Tech25 scope and we'll take a look at in much more detail. But the first thing I noticed when I opened. this is that, uh, the lack of, uh, lack of, uh, physical control uh, rods like this one here? Uh, going back to various circuit boards and if you've um, ever opened up, uh, lots of old Scopes like this I Just loved the design that went into them because all the controls on the front would have these lovely mechanical rods going back to Vertical Pcbs at the back and all sorts of things. and then they have right angle ones which ah, it was just beautiful.

but uh, all we've got here is um, most of the Uh controls here are mounted on the front panel. There's a couple which go through the vertical uh ones here. go through. We'll take a look at the horizontal, go through to a gang switch there and there's only the one rod.

uh, that's for the focus adjustment which goes all the way back to the um, uh, Supply at the back. But yeah, apart from that, it's not as elegant. It's more modern than, uh, some of the older traditional scope. So I just find it.

It's not really as exciting or is sexy. Now it's a four-board uh construction. here. We've got the front panel one we mentioned which holds the front panel controls.

We've got the uh, vertical amplifier uh panel and that it does, um, some horizontal as well. probably some time base. uh stuff because that's the horizontal going into there. Uh, we've got a high voltage, uh, power supply vertical board under there.

I Love that they've got this, um, plastic, uh, uh, plastic protection thing up the front for uh, people who, uh, start poking around inside these things. Everything high voltage is under there. and uh, then we've got the main, one main large board on the bottom of the case. and if you flip it up here like this and take a look at the bottom, you can see that's one large board.

I Love it. And once again, we've got this high voltage, uh, plastic. um plastic protection plate here with high voltage warning on it. It's nice design I Love it.

There you go. we got AC line potential n CRT uh High voltages under that? so uh, take that sucker off at your own risk and we've got some uh, 100v uh DC stuff around here. nice big, uh danger warning sign again. but apart from that, they've done a really good job of isolating those high voltage, uh uh, components and so you can just, uh, dick around on the back, calibrate troubleshoot, do whatever.

Um, with the scope operational and up in the corner here, we have a little bodge resistor. Well, it's not a little bodge resistor. it's uh, quite a decent size. um, a couple of watt, uh, beasy.

And it's um, that's obviously, um, even some sort of repair or some sort of, um, you know I don't think it's a factory mod? Um, it may be I don't know anyone else with a Uh with the same scope is your one got the same Bdge resistor on it? And there's one thing I really love about this scope. Not only the double sided layout which we'll talk about in a minute, but it's all through hole. Which means that we can access all components on the back, but every component on the back of this board. They put the silk screen designators uh, and the markings for from where to where that all of the resistors and the and the various Uh Ic's and test points as well.

It's just. it's brilliant. I Love it! Somebody's put a lot of effort into the layout of this board and my hats off to them. And of course, the beautiful part about the double-sided layout is that you can access every single component on here.

You can trouble shoot everything. So when you've got all the information on here with the Uh with the schematic diagram and the service man, you can do everything at the back of the scope. You don't even have to uh, probe. you know, get down inside the guts of the scope.

You just probe everything from the back. It's brilliant. Why isn't all gear design like this? I Love it. As for the layout itself, it's just beautiful.

If you've ever laid out a board of this complexity like a double-sided through hole board like this, of this sort of complexity, with this number of components, you'll realize the amount of work effort, and sheer talent. and AR R which goes into laying out a board like this? It's just. it's brilliant. Now, the true test of any uh, double-sided board layout to see if it's been laid out uh, properly is how many uh jumper links that you can see in here.

and well, I'm struggling to see any uh at all. There's a couple down here, but it looks like they're They're actually deliberately in there as uh, voltage test points and they're labeled um as such or voltage links so that you can, uh, actually disconnect each voltage Rail and perhaps measure the current as well. They may actually be current, um, measurement shunts. Maybe that's what they're actually for.

If you see in there, there we go. We' got one down in there and uh, it's there. There was enough room for a trace to go in there, but they decided to add a link and they've labeled it plus 8.6 There's another one here and there's all the way along here. I Reckon they're designed for uh Ser ease of servicing and E of troubleshooting so that you can, actually, uh, cut those links and actually, uh, measure the current on that particular rail.

But as for the links, I'm having a hard time actually, uh, finding any on this board. it's not easy to look uh under the vertical uh board here. We'd have to, uh, take that out. but uh, really? I you know, I'm struggling to see any link.

So this thing has been laid out with a hell of a lot of talent and care. and Blood Sweat tears I'm sure. Now there's one thing I'm not noticing inside this scope and this is something you got to really, uh, look for in uh, vintage? Scopes especially Tectronics ones are a bit famous for. It is, uh, using custom, um, hybrid, uh, modules and things like that, but it looks all fairly, uh, fairly discreet stuff.

I'm not recognizing, uh, some of the numbers of, uh, some of the Ic's off hand, but uh, they're They're certainly not, um, custom hybrid type things. although so, uh, you could say that this little one down in here is a little on the vertical board there, that custom resistor. um, that looks like a thick film resistor hybrid there. but yeah, you know.

apart from that, it all. it uses pretty much all. uh, discrete circuitry, transistors, basic, um, opamps, and uh, digital. Um, you know, 4000 series logic Ic's and so on.

Now I Just checked in that MC Motorola MC 33 46 for example, is a transistor array. It's got a differential pair plus a couple of discret uh transistors in there. so you know they've decided to use an IC instead of that. Maybe for thermal matching or uh, you know, something like that.

but um, yeah. apart from that, uh, if you if it uses all sort of, you know, more discrete components on here, then it makes it much more serviceable. Uh, because if you get one of the more advanced uh Tech scopes for example and they've got one of those uh, hybrid modules in there. If that fails, you are screwed.

You've got to find somebody who you know um, uh, still has that board, but even if say that transistor array there failed and you couldn't get it anymore, then the chances are you could actually uh, bodgy up a circuit to actually replace it. And they've been smart here. the uh trim pots that um are obscured by Boards on the Uh on the top side. Here, they've actually drilled holes in the back side of the board so that you can adjust the pot through the back light.

that I can just stick my screwdriver in there and adjust it. but you can see these ones here don't need that. Uh, because you can actually uh, adjust those from the Top If you flip it over here, you'll notice that uh, those pots down in there, these ones down here, these uh, these brown ones down in there. they can all be adjusted.

Uh, but the ones that are fouled by this top board here they will have the the Um cutout on the bottom of it. I Love it and These Warnings are really have to take heed of we're on the um Uh CRT here and there's a 7 Kolt anode voltage and really this is the dangerous inside oscilloscopes and you do not want to touch it unless you know exactly what you're doing. so you do not want to touch this. You don't want to disconnect that unless you know what you're doing.

you've got experience in doing that. And uh, the anode lead goes all the way over here and curiously, um, it is actually connected. Well, it's it's not connected, but it's um, just held down there with a with a plastic retaining clip on the vertical board. but uh, that one goes through here, onto the high into the high voltage circuitry under there and you don't want to play around with that sort of stuff.

You can kill yourself and there's your voltage multiplier in there which generates your uh, your s kilovolts. Uh, for the CRT and that comes from uh, A Mains a vertical, the vertical Mains board in here. That's why they got the big plastic cover on it with all the warning uh, stickers, and really anything in this area you don't want to, uh, poke around with unless you absolutely know what you're doing. And again, there's more warnings down in there on those high voltage capacitors down in there.

discharge before touching Terminals and You' better heat it. And we've got some power resistors here coupled into our heat sinks which are then coupled into the shazzy here and at the back as as well for power dissipation and you see that uh in quite a few places and you can see it here as well. Uh, these uh, transistors or Regulators or whatever they are are connected to their own heat sink and they were the two Uh screws that we saw on the back side of the case so that's designed to couple the heat into the case as well as well as actually retaining the uh heat sink and stopping it. uh, vibrating, uh off and things like that because if you left that larger heat sink just, uh, standing there, uh, vertical like that, you would get all sorts of uh, resonant uh modes when you transport it.

and when you vibrate the instrument. if you got on a trolly or something like that, and um, it can, just, uh, snap off and ruin your day. Now if we take a look at the Uh vertical board here, as you can see, these are the two uh, vertical uh channels here. this is the horizontal, uh, ganged switch we've got here.

These holes in there. there's actually pots down in there. there's little Um trimmer, well caps actually. uh, trimmer.

perhaps that's for the Uh attenuation compensation for each channel so you can get in there and adjust uh, the compensation for the Um for the volt for the input voltage divider. and then they've got a pot as well which is linked through to the control on the front cuz the control is not only a uh switch but um, it's also A. It's also got a rotary pot on there. you probably can't see it but there's the pot at the back there.

you can see it turning when I rotate the switch on the front and uh, the rest of it is, um, all a a ganged uh switch in there. So it's a totally custom uh thing so something like that fails. Well, you know you have to try and repair the contacts or something like that or you have to get a new board and Salvage it get a scrapped uh unit with a working Channel or something like that. but these are the sort of things you can actually repair the contacts in if you really want to go to the effort and uh, take them apart and things like that.

There's various techniques you can use and there's the horizontal gang switch and if you look carefully in there, you can actually see the multiple Channels cuz there are um, quite a lot of channels inside there and I Love the click dot dot dot. nice click mechanism. it's showing the verticals I'm moving the verticals and they have like a spongy F to them but uh, the uh horizontal um time base game switch there. really nice custom mechanism but once again, you know if it fails, you might have to um, take apart these sandwiched uh contacts or something like that and maybe uh, re surface them or lubricate them.

And once again, it's got a trim pot on the back here. and if I turn the Um Center horizontal, you can see that, uh, that mechanism in there. um, turns the turns the pot so it's you know, it's fairly basic stuff, but there's a lot of Um effort goes into actually designing a custom gained switch like that. and there's something you don't see every day made in Holland Beautiful Copyright Tectronics 1986.

So at least this, uh, top this uh, vertical, uh, attenuator and timebase board is made in Holland I'm not sure of the uh, rest of it, but uh, this board is at the very least. or maybe the entire scope is manufactured in Holland I Don't know. But uh, there we go. Copyright 986 So we have a, um, a reference, uh, point for the manufacturer this thing.

I'm not sure how old this scope was. it would have had a uh, a decent uh, product lifetime of 5 plus years or something like that, and perhaps a um, afterthought. Here, they've got some uh, decoupling uh on this particular chip and once again, it's duplicated on uh, both channels. So maybe um, an afterthought I don't know, or maybe they it was.

So it was so critical that they had to get the cap directly on the pins of the device. Who knows. but it's well done. In either case, it's uh, actually, well formed and well sold.

It doesn't look like it's been hacked on is a rather unusual looking uh trimmer cap there I Can't say I've seen one that looks exactly like that before. It's rather unusual and this one up here for Channel 1 is actually been uh bent at about 45 now. I'm not sure if that's an afterthought because it uh, could have failed this uh Focus control rod here. but um, yeah, it looks like it's been bent on purpose and the CRT itself made in USA USA USA And if you're wondering what this big coil of Uh wire is over here, that's actually a a delay line it runs from down here and it goes around the CRT a couple of times because well, it's just convenient to do that I guess and goes into the back part of the board here and you can see the structure of the delay line.

like that. it's like a plastic uh tube with the wires wrapped around inside there. some more attention to detail to make the adjustments. um uh, accessible to the user.

These trim pots here are vertical of course because this is the CRT here is right over the top and this little trimmer cap there. They've actually bent that at 45 so that you can access it I Like it. a bit of a bodge here. They've got these two uh, toroidal core inductors here with a series resistor.

They've lifted up one side of the of the inductor and they've actually, um, put a series resistor in there. Go figure. Now on the front panel: uh PCB Here, they don't really have any uh, high frequency or uh, critical stuff at all. it's just you know, controls like, you know, uh, vertical adjust and horizontal position adjust and uh, stuff like that.

everything else, um, the uh, actual um, uh signals themselves go directly into these uh cans and we'll be able to should be able to see that um on the bottom there. They might have a little bit of uh, trigger stuff going through here, but generally speaking, it's going to go uh, straight into something like this shielded can, especially when you're trying to get 5 100 microvolts per division, which this scope is capable of. Now here's the Channel One and the Channel 2 input BNC connectors and you'll see that they actually go straight over here. They're They're actually discret uh wired with these flying resistors here, straight over into the ACDC selection switch in there, which is directly on the front panel down in there.

As you can see, there's the AC coupling cap and then it goes directly through a a um a shielded shielded penetrator uh pin there which actually penetrates that metal shield down in there which is the main input uh amplifier. So it basically is just the Um AC uh DC DC coupling selection. Bang straight in. Now, although the BNC itself is actually um earthed to the front panel cuz uh, all Scopes like this are Main's uh Earth reference very uh, dangerous if you don't know what you're doing.

when you're taking measurements, you can blow the crap out of your probes and all your scope. But anyway, they've taken and they've taken an additional uh grounding a fairly um, heavy grounding. uh, strap there probably up under there uh directly as a more of a direct um, a lower inductance, lower impedance uh path directly into the vertical amplifier. They're not just going to rely on the shazzy return um, because that would be uh, that that would provide very poor uh, high frequency performance.

And there is one other uh Ro in this I Forgot to mention, but the mechanical power switch here on the front actually goes back via this uh black Rod which you see, uh, going back here. it goes back into the Um Main's input board. There's a GRE you probably can't see it, but there's a green uh Power main switch right down on that vertical Mains input board and on top of the CRT here, wedged between the top of it and uh, the top uh inside of the Um front panel here is little uh spring and that would take out any uh vibration response um, during shipping and handling and things like that just so you don't damage the CRT Now it's time to calibrate this sucker because if you remembered when I actually uh did an incoming inspection on this when I bought it. Um, it was uh, slightly.

uh, reading slightly low on all the consistently low on both Channel 1 and channel 2. uh, vertical. it was out by I don't know 10% or something. It was quite significant.

Um, so I just wanted to tweak that up and I think the horizontal was slightly out as well. So I wanted to tweak that. So um, I've got the service manual for it. Um, because that's the best way to do it.

You don't want to have to. Um, because you've seen the number of trim pots in this things it's got. You know, a dozen plus uh, trim pots and you don't just want to uh, guess which one it is. You got to know exactly which one it is cuz there's so many adjustment, uh controls on this.

There's are, uh, balance and offset and and gain and all sorts of things. And and really, you don't want to muck around with them. Um, unless, especially if all the others are in cow, you don't want to dick around on them. So it's best to find the exact control.

So the service manual says: um, r145 um, adjustment pot is the one to use for the vertical uh, gain and that's all I'm interested in. So I had to look around inside here and um I'm bugging if I could find r145 So I had to actually admit defeat and uh, scroll through the service menu here and actually find it's got adjustment locations for the where all the pots are and I Thought it would be on the vertical board, but it's not. it's actually on the main board r145 and R1 95 I think it is is the other one for Channel 2 and they're actually under the CRT So let's go find it. Well go figure there they are tucked under there we so we looked at those before um and that would have been my last guess literally for where the Um vertical gain uh amplifier adjustment pots would be I Thought they'd be on the top here in the Uh on the vertical board where there's a whole bunch of Uh pots on there.

but no, as it turns out there it in this case um R1 195 um sorry, R what is it? Uh yeah, R1 195 there for Channel 2 and this one under here channel one so let's play around with it and see if we can tweak it. Just one thing to remember when you are moving these things around. Uh, when they're powered up. just remember there can be some dangerous voltages in there even though um, you know it really sort of protects you from the dumb stuff here, but you know you want to keep away from the CRT and that sort of stuff.

and really, it's always. uh Safety First The service manual recommends using a 20 M Vol uh peak-to Peak um S Wave It doesn't uh, say it doesn't recommend the frequency. So I'm using 1 khz using my Um Tectronics 3000 Series scope here to generate that and as you can see, 20 MTS um I would have actually which is only four divisions on a scope I would have actually much preferred to do eight divisions anyway. Um, that's what it says to use so we'll just use that for starters and uh, see how we go.

So I've fed that into the Uh scope via a 50. ohm um Terminator is on the end here and let's see if we can adjust that. um, tweak that pot on the side to uh, get our to get the exact level pretty close to it. Now when you're adjusting uh Scopes like this, get yourself one of these insulated Uh adjustment tools.

There are a uh, low reactive um adjustment tool so that um, it doesn't. You know it's not metallic of course. Um, so when you're reaching inside prob it around you're not going to kill yourself. and uh B it doesn't actually add any capacitance or reactive uh components to the Um sensitive.

Sometimes if you got little trimmer Caps or something like that, you can upset their value. So get one of these little alignment tools. They cost next to nothing. Okay now what we want to do here is we want to um our input sign here.

We want AC coupling. Okay, first of all, we want to, uh, ground it like this and we want to get the position smack in the center. so we want to get smack on that Center Line Like that, switch it to AC uh coupling so that there's no um, offset issues or anything like that. And as you can see, it's reading low.

It should be four divisions. Um, because we're on five molts. Uh, per division on the time 1 because we're not using a Time 10 uh probe here of course. So I've got my adjustment.

uh, pot over there there it is. and I'm going to, uh, tweak it. and as you can see with this alignment tool, my hand looks like it's inside the scope, but it's not. It's actually all the way outside.

allows me to adjust that, um, uh, trim pot without, um, any danger at all. So we tweak that up to ah, it's maybe the position is, uh, yeah, the position is slightly off. There we go. Let's put it back and you just want it so that the top of the waveform there just touches the those four divisions.

So there we go. Four divisions Peak to Peak and I've set my generator for 40 MTS Peak to Peak and what do you know? it is spot on as well and we've uh, checked out this before, but we'll just, uh, double check. We turned up to 10 ms per Division and it's smack On uh, four divisions there for 40 m volts and then 20 obviously is two. But let's uh, go up to a higher level and uh, see if we can and see if that's spot on as well.

Okay, in this case, I've got it set to 800 MTS Peak to Peak on my generator and there you go. It's um, pretty darn close to uh, spot on I Like it? There you go. That's eight divisions perfect. and let's do the same thing with Channel Two, so we'll plug it in there, we'll switch over to Uh Channel 2 and we need to uh trigger from Channel two of course and let's do the same thing.

We'll ground that we'll take the position up and we'll AC couple that and as you can see, it's uh, short. There you go. So we have to adjust the trim poipe. Let me get in there and tweak that Now of course we could have done this back down at Um 20 M volts as they claim in the manual, but ah, we'll do it at that and that's perfect Spot on Channel 2 is done.

Now let's take a look at the horizontal here and see if we can adjust that. So if we go up here, we've got adjustment, uh, procedures here and we've done the vertical and uh, there's various things for the vertical by the way. Um, you can have a look at the Uh service manuals for these type of Scopes as well. but there's all sorts of um, stuff.

There's uh, balance adjustments. there's inverse balance adjustments, there's gain adjustments, there's offset adjustments all for, you know, very, uh, tricky. There's lots of them, so if you muck around with them, you can, really, um, screw the thing up. So let's go here to the adjustment procedures and we'll go into the uh horizontal here and uh, find out which pot we need to do to adjust that.

So it's telling us to adjust for a 1 millisecond timing and the adjustment potties are 775? That's the one we need to find. and bingo, it's on the vertical horizontal board. go figure. and uh, there it is.

r775 * 1 mag gain so that's the one we need to tweak and I spy with my little I775 there on the vertical board. so we'll tweak that and uh, try and get this horizontal waveform to pull in and I forgot to mention. of course we've got to be on Um Time 1 mode there cuz this scope has um Time 5, uh * 10 and time 50 mag as well. So they have separate adjustment controls for the magnification, but the one that you would mostly use the scope in the times one position and I forgot to mention.

before you do these adjustments, you got to make sure that the Uh calibrated uh control the actual Um variable adjustment control for both the vertical and the horizontal is all the way into the cow position because if you have it, um, pulled around, you know, if you have it out a cow like that, then you adjust it at the wrong point so it's got to be around in the cow position and there's usually like a detent um, a detent position at the end of that and uh, also, um, you don't want your times 5? Well, in this case times 10? uh, vertical, uh magon either. There we go. Uh, use the fine control here to adjust the waveform over like that because as you move it, it will actually, um, maybe you know if you leave it in the center it should be fine. But there we go.

It is spot on. I like it. and let's just, uh, check that it's still okay in the mag position I'm inan times 10 magnification down here I'm in mag mode. You can put it in Alt mode where you can get both Uh waveforms up at once, but we'll put it there and uh, it should still be.

Oh, it's slightly, it's slightly off. ah, half a be's dick, but we can actually tweak that one too using Um R 7 which is another control on the board here right at the back. So let me tweak that. this is the time.

10 mag control. So there we go. Spot on. Just tweaked it.

just a tad perfect. and X 5 mag mode here wear out on that one as well. So luckily we have a pot for that. It is uh T it is R 731 so let's get in there and tweak that one as well.

Here we go and bingo near enough to spot on I like it and just go back and check that they didn't uh interact with each other. Times one wear spot on there if we go to Mag * 5 Yeah, the offset's a little bit out there, the horizontal offset that is, but that's fine and time 10 mag beautiful I like it. Yep, spot on and we can go into time 50 as well if you're really, uh, really pedantic, but there's no separate control for that. it uh, must use the other two and and it's pretty darn close.

it's a little bit out, but uh, there is no adjustment control for that one and we'll just do a few quick spot checks on the other horizontal Uh ranges. I've got 100 khz signal this time and it is spot on. No problems, uh at all and you can check the Uh mags again for that and uh, yep, just fine. So let's take it up in frequency and see what we can get and using a 10 MHz signal.

once again, we spot on it. x 5 mag gain I've got it because this Um scope isn't particularly high bandwidth on times one mode. that's as far as it goes. so I can't get the Uh 10 divisions actually across there.

but uh, in any case, um, we can turn on the X 5 mag and we are spot on beautiful. I Like it: I Think we've just, uh, calibrated the horizontal and the vertical gain channels. Let's actually count the pots in this thing that I can see one, two, three under there. Four five, 6, 7, 8, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 Uh, two under the CRT Um over here, which we actually, um, did.

There's a bucket load of them and there's ones on the bottom um of the main board as well. more adjustment pots you can poke a stick out that's not even counting the um, uh, trimmer caps and things like that for all your uh compensation adjustments. Crazy. Just imagine having to adjust the things at the factory when they first roll off the line and all the pots are at Center and all the trim pots are at Center or wherever and you've got to tweak the thing.

Oh man, you go nuts now when you're adjusting stuff like this. not just Scopes, but any bit of electronics at all. The most important thing by far is the angle of your tongue. If you don't get it right, it's not going to work.

Your adjustments are going to be completely out and Murphy will get you every time. Tongue Angle: Number One Watch. This is the correct technique. See, it's sometimes left, sometimes right.

Varies between the individual, but trust me, super important. Catch you next time! I Almost forgot the most crucial adjustments. You can't do them with two eyes, Must have one eye and the correct tongue angle. Let me demonstrate.