Hi In a previous video I showed that my fluke Stephanie and B multimeter which I basically have had just had sitting in a box here on the shelf. I because it's not. you know it's not something I'd typically use every day. I've got a better nicer meters than this one, but anyway, um, it looks like it is like died that I don't know what has gone wrong with it's just been sitting in the box.

Check it out! I Mean you know and obviously like the the chipsets working, you know display comes on. it seems to do. or you know it appears to work when you actually turn the thing on. but like nothing.

look zippity-doo-dah and no, it's not the test leads. I've tried various functions, it just does not recognize anything at all. Has the input blown or something like that? I have no idea as far as I know I haven't used it for. you know, anything serious since I got it in a mail bag way way back quite a few years ago now.

and um, yeah, I think I did a quick teardown on it once, but that was like it. So anyway, let's crack this sucker open and have a look. And of course, yes, this is the made-in-china fluke. and just like the original, this actually reminds me of the Fluke 19, which was further flukes our first foray into the Chinese-made multimeter market just to test the waters.

Here it was at. The Fluke 19 was a here's a photo of it I grabbed from the internet I don't have mine anymore, but I bought quite a few of these for work because at the time they were a big deal. They came out it was like I think it was sub hundred dollars and for a fluke that was absolutely incredible. you could buy it in the local Tricky Dick store and it was Flukes first entry into.

You know they'll just testing the market to see if people would want or like a Chinese-made fluke and they only sold it in Australia a couple of other Asia-pacific countries and that was it as far as I know and it was a complete and utter failure Oh don't almost every one of them like died. They had this fault where the chipset would get killed I can't remember the details but every one of the ones I had died I've got tons of reports of him dead there were at the time this was probably back in the late 90s perhaps? I think it was a long time ago in a galaxy far far away. but yeah, it was a miserable fire fluke 19. but obviously.

well, yeah, they did a second suck of the seven. Hey, we can still do this. The Flukes 17 B just start out as the 17 then I went to the 70 MB I'm not sure. Anyway, let's crack this thing open and dumb, see if we can find out what's wrong with it.

And yes, the good thing is we have the schematic. Awesome! So if you still got a work in Flook 19 B Well you're one of the real lucky ones. You've got a rare instrument there because I think most of them on the market died I'd love to find out the exact reason it was something to do with the chipset ASD sensitivity or something weird like that. Anyway, this one failing.

just sitting on the Shelf there does not instill a lot of confidence in me. Hmm. now I don't know about you, but that non-standard spacing on the amps jack there gives me the heebie-jeebies. All right, let's crack this thing open two double A batteries.

lots of Chinese writing on there. Thankfully you I can understand the fuse ratings and let's whip it open see if there's anything obvious in here. Give it the smell test. Nope.

nothing smells burnt and nothing right off the bat. Oh oh oh oh look, can you see what I see or don't see? don't Well, there's your problem that is hilarious. The screws are not on there I think this is a massive peg kak I've as I said I think I've done a teardown on this before and obviously I did not put the screws back. Oh well, there it is I fixed it I'm pretty sure it'll now work again.

Yep, no worries. Well I could have just deleted this video. but and what funds that? I've got a schematic I can salvage this I can salvage any video no matter how tragic it is. Alright, let's just I don't know, have a look at things.

why not me and I just checked in. Yep. I have actually done a full teardown video of this episode number 344 to be precise. No wonder.

I don't remember it I'm going to do this one day. I'm actually going to, you know, produce the exact same video I've done like five years ago or something and I won't even realise. anyway. Um, yeah.

so I won't go into huge detail about the construction of this thing I've done that in the previous teardown? Unsure. Suffice it to say that that's one of the wimpiest tenets Current shunts I've ever seen. Look at it. Little an EB thing.

And the other thing that strikes me about this is of course, these adjustment pots. Little one, two, three, four, five, six. is there have I missed one? seven, eight, eight adjustment pots in this thing. They're adjusting for everything.

Why are they doing that? Well, You know, like every modern multimeter you know no longer has, they're all close. Kate What's called closed case calibration you don't have? There's no pots inside to actually trim, but this thing has trimming for almost everything. Why is that the case? Well, it's just using a single chip set here. We'll have a look at the actual chipset itself in a minute.

But and so it's just a regular, off-the-shelf multimeter chipset. There's no secondary processor that, actually, because basically multimeters can come in two varieties. Well, probably three varieties. Actually, one is just like this one.

As simple as it gets. One multimeter, specifically purpose designed multimeter chipset. There's you know, three or four manufacturers on the market who make these and it does everything. It does all the multimeter range switching functionality.

Measurement: ADC it drives the LCD. Everything else does the whole shebang. The second one is to use a multimeter, which is probably more popular these days, especially in the mid to high range. Meters is to use a specific multimeter chipset.

but it's only a front end chipset, so it only does the measurement hardware. You know the front end, the range switching, the ADC, and you know various generators and all that sort of stuff. and that is just a front end. It can't actually do anything itself.

It's not really a processor, can't drive an LCD, can't do anything else, usually a serial output, which then goes to a secondary, our processor which then drives the LCD and everything else. Now we can actually do a comparison with the new Eevblog me to the Be M23 five here and have a look at this one and you'll notice this one actually uses two chipsets here, but this one is a little bit unusual. Usually when you see two chipsets like this, you'll have just a multimeter front end chipset like this which doesn't contain a processor as just as I said before. like the range switch in everything else.

the ADC All that, all the stuff. you know, the true Rms converter every you know everything else. All the other functionality required for a multimeter chipset. I Put a typical wire datasheet over here of a chipset which is are fairly common.

For example, Now this one. You would think that that's the case and it interfaces with the processor over here for the serial. but this one's a little bit unusual in that no, this one is actually a processor and does everything just like this one up here, but it obviously does. It's designed for a rack close case calibration.

It's got a squared prom building because it's got to store the contents and it either has a squared prom built in for the to store the software calibration functions or can use external a square prom. But this one actually is this secondary chipset here. our link in the datasheet here and it's actually just an LCD controller chipset so obviously couldn't get enough pins on this thing they needed even though it's a complete multimeter chipset with processor and everything built in requires external LCD controller. So this one's a little bit unusual in that respect.

but it's more common to find a multimeter chipset and then a secondary processor. Now there's nothing stopping a single chipset multimeter like this one up here from having closed case software calibration. but the the actual processor inside here is not designed that and for that, it's bare-bones It's designed not to have any of that closed case calibration. I You know, a squared prom built-ins I can store our you know calibration settings and things like that and compensate.

It's designed to use these external trim pots around here, so in that case, it's A. It's a poor choice by fluke in a modern multimeter to have to require pots like this to trim it just from a long-term you know, drift characteristic and everything else. It's at this poor form, not when you know modern processes can handle these sorts of things, but hey, that's typical of these. Really cheap are slow in chip sets like this.

They require these external pots for those who want to know what the front end multimeter chipset on the Eevblog meter is. sorry Secret Squirrel. So anyway, I think that's pretty poor having these and trimpots on a mold and mouldy meet up just dear fail. Anyway, now let's take a look at the schematic now.

I'll link in the complete schematic down below. It seems to be the official one, so I'm not sure proprietary, sorry fluke. but once it's on the internet, it's on the internet. So yeah, there you go 2009.

It was generated anyway yet so it looks to be a genuine. It's not like a reverse engineered or anything like that. And I'll link in the PDF down below. Now, the chipset in this thing.

They've mainboard somehow I Don't know when they convert to PDF they're mangled that, but it's actually an F S 97, 21, the LP 3 version and I'll link in the datasheet for this puppy down below. And yeah, it's a complete multimeter chipset for TF SSR Fortune Semiconductor. They're one of you know, three or four different makers of multimeter chipsets that is still around these special chipsets. and as you can see, you know that pretty much handles everything.

It is a single chipset, one chip to rule them all, and this miscellaneous stuff around. So let's actually just have a quick look at the schematic, see what we can see here. First of all, take a look at the current jacks here. and I have done a separate video on multimeter input protection.

So if you want to know all about diffusers and how they do things in this diode bridge here and things like that, which by the way is just our clamping, That's basically what they're doing. they're clamping the voltage then I'll link that one in as well. If you haven't seen, it's well worth a look and look. they're actually trimming.

These are the shunt resistors. Okay, so this is the here's the 10 amp input here. Here's our common Jack Okay, so our 10 amp goes through our HRC fuse of course into our typical 10 milli ohm shunt resistor. That's that real wimpy look at it.

It's real wimpy look. sorry I've got fixed contrast that fixed exposure on the camera here. That's why it's all dark. It's very difficult when you're doing white paper like this.

You've got our set manual exposure on the camera anyway. ten milli ohm current shunt which is all fine and dandy. and then they're doing a trim across that sewing typically what? which actually is okay. You could probably argue that one's not that bad.

So they're doing a divider. here. they're doing a voltage divider. There's 100k resistor 47.

They're actually trimming that. That's a large. Thats a large trim range that's absolutely massive. So yeah, I would have limited that.

I Think that's a bit of poor design work there. Anyway, Usually they physically trim the the nichrome why our current shunt. Typically, it's made out of nichrome wire, the current shunt and they'll physically trim it either by taking a little chunk out of it or adding some solder. You know, getting some pliers on there and getting given a little crimp or something.

Just you know. change the value by, you know, half Abby's dick or something like that. So they've decided to add a trim pot and that's rather unusual. Most companies are just decide to trim it some other way or with the modern chipsets are just software trim of course.

Okay, so on the milliamp range here, here's part of the range switch. They've got this range switch actually split all the way through this schematic as you'll see and what this is showing. These are the physical contacts on the PCB. So when you put it in the milliamp position down here, it's shorting out these two contacts.

What does that do? Well, It shorts out this resistor up here. So here's our milliamp input jack. So if this resistor is shorted out, then this one Ohm resistor here is going to be our current shunt resistor. Actually, it's one Ohm plus this 10 milli Ohms down here.

and you'll note that they've got another. They've got a 1k resistor in parallel with that. so they're just, you know. trimming that down slightly because they want to get it down because you you want this.

This should be like point 9 9 Ohms. Really. So that's what they're trying to trim it to because it's in series with this 10 milli ohm 10 amp shunt down here and then in the micro amp range. This contact is moved from here up to the top.

So then we've got this 1k resistor in series here and you'll notice this is 0.1 percent. This one here was only one percent tolerance for the milliamp current shunt. It didn't You know? They once again, it's all about the Temko. It's not about the absolute tolerance because this thing is actually trimmed, but you'll notice these ones a point one percent here because there is no trimmer for the micro amp range.

So that's why they're using precision resistors in here because it's actually not easy nor cheap to get a 10 milli ohm current shunt resistor. My I do that I use a 10 milli ohm current shunt resistor on my micro current, for example. and it's an expensive resistor, even in thousands and thousands of volumes. It's you know, upwards of four dollars per resistor, right? It is really expensive.

So yeah, if you want the precision, you know straight off the bat without having to trim the thing, you know mine's up. But what is it? Is it? Point oh, five percent I can't remember. Yeah, I Think it's a point Oh, five percent or point One: Nine Point One percent is it? Yeah, that's actually a very expensive resistor. Hence, it's actually cheaper per unit to just have somebody trim this trim pot here.

Yeah, labor takes time, but Labor's not that expensive compared to a four dollar resistor. It just depends on which way you want to do it. So yeah, they've decided. Note: we don't want to trim Oh for that because the 1k ones.

These low values one these low values of 1 ohm and 10 milli ohms. They're expensive to get in real precision values, but 1k is not like you can get those for 10 cents in volume or something like that, right? Real, fairly cheap, right compared to these. So so they're able to use precision resistors for those and no trimmer, and you'll notice the sense voltage here is actually tapped off. Different position depends on wherever where in the Amps range or whether they're the milli a brain.

So they've got another set of contacts on the range switch here, which in the amps range. Of course it taps off from this voltage divider across this 10 milli ohm current shunt resistor in the middle amp and micro amp range. Up here it's the same contact, then it taps off the top here and when it's in milli app range here, it actually taps through this resistor onto there. So the current shunt resistor is 1k in parallel with a hundred and 10 ohms, then in series with one ohm in series with the 10 milli ohms there.

But it's actually strictly not true to say that there's no trimmer for the micro amp range here. it's not for these resistors, but because it's still in series with this 1 ohm resistor in parallel with this 1k here. if you actually have a look, we bring this in here and we have a look what we've got. We've got 1k in parallel with 110 up here.

so that's ninety-nine Point, Nine Nine, and zero 999. But I'll live the rest off anyway. It's that in series with So plus one on the 1k here. but that 1k is a trimmer.

Ok, so that's actually 0.999 if it's just the 1k. Okay, if you haven't trimmed it lower than that, plus the 10 milli ohm current shunt resistor down here, that's a total value of maximum value, not including tolerance of a hundred point 108. So these two down here are this one down here. It's It's way too small to affect.

It's up in the 47 K range cup. You know, orders and orders of magnitude higher than the 10 milli ohm, so it doesn't affect it. It's only for when you're out tapping off the amps range here. So obviously they have to trim this 1k here.

It's it's going to make a difference. They want that to be like bang on. Okay, because this has no software compensation at all. So they want that to trim this value right down here to exactly bang on 100.

So that trim part actually will find actually affect both the milliamp and the micro amp ranges. And then they've just got two high value input protection resistors here. So because it's going directly into the chipset, they're just for some current limiting protection for the input pins here in case there's a slight possibility of overload. And they don't have to be precision.

of course, because this is high input impedance. That's why you've only got one percent tolerance. They're just Joe Bloggs resistors. Now, let's take a look at our Volts and Ohms input down here.

This is our input jack and then we've got five resistors in series like this. and they are these puppies in there. There they are. Why have they got five like that? I've explained that? in the previous video.

it's to get a high withstanding voltage. So each resistor has a certain voltage. you know, maximum voltage time. So you whack five in series and you can get a fact of Li a high voltage resistor there and that's cheaper.

Five of those is cheaper than you know. One big one, which you'll typically find by the way, Tada in the Eevblog meter. There you go. This is more expensive and notice the isolation slot under there.

that's a high compliant voltage ceramic resistor much nicer than just the five, but you know they get away with it. I Mean you know nothing inherently wrong with that. You'll notice that they've got 1.5 mm there and also here. Now a real educated guess is that this is actually a design note to the PCB layout person to saying: we need 1.5 millimeters minimum clearance on these things.

That's what we need because these are the high voltage input so isolated from everything else. And this one here. Nine millimeters input clearance. Thank you very much.

So, assuming that we're in either the Mille volts DC range, the Ohms or the capacitance range, then these two contacts on the PCB here are going to be shorted. and we're going to be using these input v input resistors here for that particular mode. And if we follow the yellow-brick road here, let's go over. let's go over another protection resistor here.

We've just got some diode clamping here. What are they? Bev 199's Are they so got some dire clamping? And it's also fairly typical, especially old flukes. I'm not sure if Fluke pioneered it or not. I was kind of gonna maybe do a separate video on this.

it's on. Try and find a another fluke meter schematic here which actually shows these. and yes, actually found it. Here's a schematic from the Fluke 77 series 3 which are there when actually comes from way like even much earlier multimeters.

I Think the Fluke 45 had it. and you know, all sorts of real old-school flukes have this dual transistor arrangement where it's basically they're configured as back-to-back diodes, so it actually uses the the breakdown voltage of the transistor to actually act as a Zener and then having the two actually acts as a back-to-back zina because one will have the forward drop and the other one will actually have the breakdown as the Zener depending on whether it's positive or negative input. and it's a rather unusual configuration, but very popular. so I'm not.

If anyone knows the history of that and whether or not Fluke actually pioneered that, then I'd love to love to actually know details on that. Anyway, back to the 17 being here. Yeah, they've just decided to use some 599's Mir Now this part down here is rather interesting. It's it's a different configuration to what I was mentioning before with the back-to-back Zener clamp in there.

But look, if you put it in DC volts or AC volts mode, then it's basically shorting out this right so there's nothing there. Effectively, nothing there at all. But what they're doing is actually tying VSS effectively. This is where the coupling VSS into the common terminal.

The common is actually the terminal over here. So the battery negative VSS is actually the battery negative. If you go up here, there it is. so it's they're not directly shorted together.

They tie it through this one MIG resistor here and on the base of this transistor. Q1 Here, they've actually just got a reverse biased diode there on the base of that thing. And they've got a PNP here. So it's basically they're shorting out that this goes up to you.

Follow it up Yellow Brick Road again. it goes up to the bottom of our resistor divider. Here you so these are our range divider resistors here, handled by our multiplexing inside the chipset. and basically the common of those is shorter down to ground.

We're measuring AC and DC, but when we're measuring Ohms, it disconnects the ground and it's you know it's go. It's activating this part on the lower end of this resistor network here in the Ohms mode, and the capacitance mode. here in the Volts DC mode, they've got an AC coupling cap here they actually and a and a series resistor so it's almost like a little snubber. There are shorting that out and then our input goes by the way through a PTC positive temperature coefficient resistor which will increase in value in overloads.

And that's that puppy down in there. Sorry, silly thing. There it is. There we go.

There's our input PTC resistor and then our big 1k. Here we go. they. This is where they have a note saying install either one of these.

So install that or install that. So there's 1k resistor here in series. That's very common input protection for me. You know it pretty much handles.

This is how why you can put mains on the Ohm's range. for example, because you've got the PTC resistor here, which will increase in value with any overload. Got the big beefy 1k high voltage resistor here and no worries whatsoever, and without clamping and everything else inside here, then no worries whatsoever. Because when we're in the Ohms range here by the way, we're actually we need to force a current out into the then to the positive Jack out here.

So that's why it's switch in this range. Switching is both used for our DC and AC voltage ranges plus the owns range as well. It's rather quite quite clever. So they're actually switching that in this particular circuit in here when they're generating the Ohm, so you know it's like constant current type thing out for the Ohms range and likewise for the capacitor too.

Because basically when you measure again, how they do the capacitance measurement, they just basically have a constant current output and then they just time chipset just times how long it takes to charge up. Bingo! You can work out the capacitance and then of course the way that they're tapping that off. Not in until they have to generate the constant current from here like this, but they also have to read back off as well. so that's why in the Ohms range here.

Also, Bingo, it's tapping off like that. So that's the voltage sense in there. and the chipset can actually measure the voltage across the resistor under test. So I Think they're attempting to do some sort of clamp in here in the Ohms and the capacitance mode.

but to what end? I'm not entirely sure because at low voltages, this circuit is not going to engage. It's not going to do anything. so you know, add a couple of volts that we're talking about When you're operating the Ohms mode, then this is not going to do anything but a higher voltage is yet. it's going to start to conduct.

So yeah, presumably some sort of attempt at clamping. and this is not a true RMS multimeter. So there's no true RMS I converted chip Everest separate analog devices One which is quite typical, or the Eevblog meter, for example, is a true Rms multimeter. There it is, but you won't find your traditional analog devices true RMS converter chip in here because it does some clever stuff using external components in the main multimeter chipset.

Might have two separate video on that one day. Anyway, this so this one's an average responding meter. And here's the AC average responding circuit control via the chipset here and being out. Another trick.

Another trimmer in there for the AC calibration. Bloody Trimmers. Dodgy as and it looks like they've got a amplifier in here. Yep, Oh P that'd be Op amps.

So they've got some internal Op amps in here, so you'd have to look at the data sheet to get the internal arrangement for this. But basically so, there are feedback resistors for our non-inverting Op-amp with the times 10 gain there. Now some multimeter chipsets. They'll have a combination of standard Op amps in there.

Plus, they might have a for amp in there as well that you can select with the internal MUX in. So that's you know. Not uncommon because the chopper amp very precisely. You know, no bugger-all DC offset.

So you might find those on, say, a higher end four and a half digit multimeter chipset. And there's our DC calibration trim pot. Looks like that's is that hooked up to two reference pins. We really need to look at the data sheet for this.

Getting an internal block diagram to get more fancy pantsy. Speaking of fancy pantsy, look at this. This is quite unusual. You don't often see this in a multimeter, so thumbs up to this.

We've got um, Cold Junction compensation and that's for the temperature mode, so you'll notice that when we select our temperature on the range, switch here. Bingo! It goes up to here into this amp here, but then that's offset with a cold. Junction compensation I've done a video on cold Junction Compensation: We saw a Waco over it again, but awesome. That's what high-end our thermocouple amplifiers and our thermometers like hang On I've got one here somewhere like this.

Fluke? okay type, you know, a fluke. f3000 I've done a teardown of the of this and various others and these have that cold Junction Compensation on the input pins Here they have a temperature sensor which takes into account the temperature of the dissimilar metals, which can cause offset errors in your temperature. So they've actually added that in here and you'll notice. Look there, it is a temperature sensor.

And once again, the the designer has put a note in here for the PCB person place near the inputs because it's got to be right near the input jacks. Brilliant! I Don't know why they bother doing that, but it's excellent. I Mean this thing's you know it shows, has tried to build it down on cost. but hey, Cold Junction and compensation? brilliant And you'll notice there it is, you fall down there.

There's our little temperature sensor right down there. but really, you know in this case it doesn't like matter in your proper ones like that other fluke thermocouple meter I showed before. It actually physically couples the chip through to the middle of the input jacks and this one's just physically close. It's not doing that, so it's and you know it's a little bit how you're doing, but it's I Guess it's better than halfway up the meter.

But yeah, in the scheme of things, doesn't really matter here. But yeah, they've gone to that effort. So I'm very, very surprised. And they've got a offset trim pot in there as well just for the temperature.

So they you know they really did take this thing seriously. I Guess maybe not surprising. I Mean it does have a specific, you know? maybe that was a big selling point they wanted to do. this thing does temperature and does it probably better more accurately than your average multimeter.

There's not much else doing here. Got some miscellaneous looks like some filter stuff maybe happening around here. Ah, there's our main oscillator for megahertz and direct LCD Drive up here and Bob's your uncle. That's about it.

I'm some extra, right? You know the buttons and things like that, some extra range stuff and well, not much. Well, what are we got here? our MUX Yeah, there we go. 7, 4, HC 1, 4, 8 our priority encoder. So they basically got some pull-ups and pull-downs here.

just the range switching. so they're basically just detecting which so the chipset can detect which range is actually currently selected. So there you go. I Hope you enjoyed that I Hopefully I Managed to salvage this video was supposed to be a repair of this thing and sorry fluke I I Thought this thing had come a gutter and failed on me but don't it was a peb kak screws when I previously put the thing after the teardown.

Are these those things happen? You know? Ah geez. so that was better than deleting the video. I Hope Anyway, hope you enjoyed it. If you did, please give it a big thumbs up.

Catch you next time you you.