Hi it's retro product review and tear down time and today I've got the Classic Fluke 27 multimeter here. It is great! eBay Score! I Picked it up for $40 us. Practically brand new. Buy it now.

Can you believe it? Damn right. I'll buy it now for 40 bucks. Uh I Love this meter. It is a classic Fluke meter.

It's been around for decades. It is their original. Super Rugged Waterproof multimeter Dropproof 3 m dropproof Uh, waterproof to I don't know a meter or more? Uh, just like the Fluke uh 28 Series 2 which you've uh, seen me torture test and fluke. Was still selling this puppy for many decades, right up until they released the superseded model, the Uh 28 Series 2.

This is the Fluke 27. It's also available as the Fluke 25. Um, there's just some functionality differences. It's only got two buttons instead of Uh four.

So the Fluke 27 is the one to go for and it's available in several variants and different colors. This is the latest model which is Cat 3 input rated. It's because this thing was designed before. Well, this model was designed before the Cat standards were even thought of and came around.

Uh, so this new model with the yellow uh Cas in plus the charcoal uh fa up panel on it. This is the latest model which I believe is the Cat 3 rated model. If you get just the yellow one or just the complete charcoal color one, that's the older model and you'll find that doesn't have Cat 3 ratings now. I'm not sure if they've actually changed the circuitry in there or they've just rated it and rebranded it, tested it, and rebranded it as the Cat 3, but this is a really great meter to to pick up on.

eBay Why? Because it's not only super rugged and it's a fluke, but it's also pretty darn accurate as well. It's only a 3200 count. So basically, uh, 3 and 1 half digit, uh, multimeter. but it's got 0.1% accuracy.

Normally a 3 and 1 half digigit meter. you know, 3200, 4,000 count, Whatever you're only going to get .5 Or3 or maybe2 if you're lucky, this one's got .1% DC volts plus one count so there's not much Plus in that final digit there at all. It's a pretty darn accurate meter and it'll last you a lifetime. And yes, it does have a lifetime warranty there.

It is terrific, so let's take a look at it, do a very quick summary review, and tear down. Love it! Now the first thing you notice about this meter is that it is big and here it is compared to the 875, which is already a pretty decently big multi. As multimeters go, it's but technically it's probably just a fraction longer and the same width. And it is, well, basically bigger than it's uh, the 282, which is its new Um counterpart.

So, but of course this one's got the holster. Of course this one does not come with a rubber holster and it's still rated for 3 m drop. Can you believe it? Because uh, Fluke famously claimed that it, uh, contain that. it has uh, plastic twice as thick as their regular multimeters and impact resistant polymer plastic in them.

So, um, a really super duper rugged meter. And the other thing you notice is that it's bloody heavy. That's about 3/4 of a kilo. Let's get the scales out here.

Give the 875 a go. It's smidge under 600 G there. And what does this suck away? 673 So it's heavier and it doesn't even have a holster. hence all that thick plastic.

And there's probably a lot of metal in these things too because they are, um, very immune. uh to external. Emi And let's have a look at. and there you go.

It's basically the same as the new 282, so it is a big chunky meter. but I Just love it. And the tilting bail on it you can see here is really quite remarkable. It's huge and wide.

I Absolutely love the thing. There's no way this suck is going to fall over when you're using it. Beautiful and on the bottom of it here. we've got some, uh, nice rubber strips down here to stop it moving around your bench.

Really quite nice. I Like it. and we have a removable battery compartment. This is technically the Fluke 27fm.

Now this is an interesting, uh variant. You'll see this: Sometimes it's written on the front of the meter here, sometimes it's branded Flute 27fm there and I Believe what FM is is it stands for for military? In other words, it was a specific model uh, they they released for the military I believe it's an absolutely identical meter in every respect. And as for the front panel, of course this is the new charcoal and yellow model so it is Cat 3 speciic specifically Cat 3 input rated 10 Amp Jacks 3200 Milliamps and Uh, Volts, Ohms and Diode Jack with standard uh, spacings and shrouded of course. and the range switch itself though I really love the rain switch on this thing.

Not only does it feel absolutely beautiful and it's designed to use with big gloves on and things like that so you can easily switch it. But what I love is that it's basically split down the middle. There's two off positions there and but this half is basically all AC So you got Volts, Ac, Mill Volts, Milliamps amps, and micro amps and Ohms happens to be on this side because, well, it's got to be somewhere. So basically, if you switch it in this direction, you know you're getting DC None of this pressing button to change to Uh AC and DC mode crap I Love it! You just move it all on one side or all on the other.

Functionality wise, it doesn't have a huge amount. unfortunately. it's just got standard Mid Max the fluke touch hold the relative mode and uh, the range hold. Um, but there's no capacitance.

Capacitance wasn't around on multimeters when this thing was designed and released, but it, um, it does have a fast updating bar graph display down to a couple hundred microsc or something like that. So really, super quick. Uh, bar graph. But if you just want a super reliable, super rugged multimeter just to measure your traditional volts, Ohms, and amps, it's this one's hard to beat.

And on the Ohms range here. even though it's not written there, it does have conductance or Nano cement range. you just hold down the Uh R just press the range button twice and it puts it into Nano Seens great for measuring leakage and stuff like that. Now there is a bit of a delay when you turn the thing on.

There, There you go. It's a bit disconcerting. At first you think oh no I've run out of battery, but no, trust it, it'll eventually turn on and the display is. Even though the digits aren't very large, the contrast is is actually very, very nice from pretty much any angle.

So there it is side by side with a Fluke 87. And as you can see at this particular angle, the contrast is much better on the old Fluke 27, but there's no backlight uh, capability at all. Just be aware of that and from the opposite angle, it still beats it. Let's check inside the battery and fuse compartment.

Metal threaded inserts on all four screws. Lovely. and it just lifts up completely o-ring seal because this thing is, uh, waterproof, dustproof, oilproof, everything proof. I Love it.

And you know it's there's nothing fancy here at all. It's just a loose 9volt battery, but it does have the foam on the bottom to keep it in place, so it seems to work reasonably well. Yeah, it's just your traditional battery snap, but they've got the spaghetti or is that heat sink that looks like oh, sort of really heat shrink tubing. It's like rubber tubing or something like that.

It feels feels very rubbery. Anyway, they have done that to protect the wires so they don't get pinched and stuff like that. And if we take that out and get in here Tada We can get access to the two HRC fuses and they're 440 milliamps and 11 amp fuses for the two. Rangers And the nice little Fuse cover there stops them from uh, coming from, you know, vibrating out, popping out, and coming loose.

I Like it. But probably the thing that most impresses me about this meter is the battery life. From a standard 9vt battery, it has got a rated 1,000 hours battery life. Yes folks, four digits.

Can you believe it? It's a stuff of wet dreams. Really in a multimeter? Beautiful. I Don't know another multimeter on the mark Market that matches this thing and this thing is what? upwards of 20 years old now? Unfortunately, there are a couple of more downsides to the meter. The uh, diode range only goes to 2 volts maximum so you can't test white leads with it and the continuity buzzer.

Unfortunately, the bar graph is going there, but it takes some time so it doesn't even pass the slow scan. Pro probe test. Look at that right it? It takes some time unfortunately, but it is fully latching and well. I did get this thing on eBay So have I bought a dud.

Let's check out the resistance range first. I've got my resistance standard here. point5 percent 10K bang 10K You better believe it. Let's try 1K and see what we get.

Ah, spot on and let's try my EDC MV 106 voltage standard. This is a 3200 count meter, so let's put it on 3.0 volt shall we? And let's give it a go. Spot practically spot on. There we go: 3.0 and two one.

No drama whatsoever. Let's take it all the way up to 10. Not a problem and let's take it to 300 M volts. Ah, look at that least significant digit.

Nothing doing there. Spot on. Absolutely spot on. Fantastic winning score on eBay Beauty.

and I Use my Keithly 225 current source that should be 100 milliamps and it's close enough. Well within spec. Well within spec. 10 milliamps.

Yep, spot on. Let's go down to 100 microamps. sorry one, that's that's 1 milliamp. There we go: 998 Beautiful.

Certainly close enough. Let's go down to 100. Yep, spot on 10 microamps. Beauty Just another thing, it doesn't have no input jack alert for amps.

None of that fancy modern stuff. blah warranty void if seal broken, screw that and the screws in this thing appear to not, uh, fall out when you unscrew them. but they do eventually pull out. and yes, they are.

There is no metal threaded inserts for these ones, but you should never have to open the case on this is o-ring grommets down in there, so just be careful of those. If you want to maintain the waterproofness of this thing, you have to be extremely careful what you're doing. So let's crack this puppy open and wh, there's our o-ring Oops, just be careful of that. But ah, look at all that shield in and you'll notice the Fairly deep ridges around there that go right into the top part of the case there.

and there's good blast protection there. So if this thing goes Kaboom inside, it's not going to escape very easily with those High walls and the O-ring Very safe meter and the input Jacks Here are solid metal uh posts with Shake proof, washes under there and screwed directly into the PCB but the fuse PCB as you can see is on that vertical Riser board down in there which is uh solded directly onto the board. So the board is uh got these cutouts in them like little tabs which then feed through the main PCB here and then they're solded directly onto the board. It's rather novel and as You' expect on a fluke, the soldering quality is absolutely first class on that Riser board.

But I guess uh. the only issue with that Riser board is that it could potentially are those solder joints could potentially uh, crack with uh when you insert and remove those fuses because all the pressure and the flex on the board. But I think they've done their homework on that and it's going to be rigidly held in place so that shouldn't be an issue. And you'll notice on the side here how it's also shielded.

but then there's uh Brakes in the shield there for all the calibration, trim pot adjustments. Love it! And one of the big features of this meter is it's very high. um, electromagnetic immunity. hence all the shielding and everything else around.

It is really a very nicely shielded unit so let's pop that off. and uh, it's not easy to take this thing apart. Looks like we're going to have to take the Jacks out to get the whole board out. Um, it's a multi-step process to take this apart, hence having the adjustments on the side there so you can adjust and cow this thing without having to, uh, take disassemble the whole darn lot.

And the funny thing is, even when you take these screws out on the top of this Shield you can't get it out because there's actually an embedded threaded nut in the shield itself. There's two of them embedded in there which are unscrew from the bottom. So I've got to take this whole unit out before I can even get that darn Shield off. And one interesting thing to note is that there is a bit of wiring on these input.

Jacks I Mean this? Jack absolutely goes nowhere. It's got no components or anything on the bottom, but it's got that wire flowing off down further into the board. and likewise for this one. but there is that, um, input hybrid and that ceramic hybrid resistor there, um, across jumping over from there.

But apart from that, they do, actually. um, have the wires coming out from there and this one's actually been pinched. So I'm not sure what. uh, what happened there.

but uh, that one certainly has a bit of a rough life there. once you get those four screws off for the input. Jacks There, it does look like it just pops out. Okay, it's probably a connector for the LCD or something.

and yep, that's exactly what I thought it was just a 01 in header. There just required a bit of force to pull that out and I found something rather interesting already and that is Fluke 27. There it is. Rev Five of the board.

Interesting thing is, this was actually redesigned in 2003. There it is. Copyright 2003 Fluke PCA digital Rev Well they've got a manual rev 8 on there and uh, it looks like a fairly modern uh display processor down there. I'm going to uh, that's been Pro like microcontroller so I'm going to whip that label off and have a look what we have down in there.

So it's saying version two there and I think we might fine. This is a TI MSP 430 like they use in the new model Fluke. Let me get that off and we'll see. And bingo I was right MSP 430 f437 There you go.

So they decided to redo this sucker. Maybe they couldn't get uh the Asic chip or something that uh, they used in the original model so they clearly redesigned this uh display board down here. it' be inter in to uh compare with an original flute 27 and I used to have an original flute 27 a long time ago but unfortunately I don't actually remember and don't have any photos inside. But they've clearly redesigned this in 2003 and you can see the uh classic design fluke mechanism there with its uh, four arms going like that.

That thing is never going to wear out and they've used a Kyo Ser brand uh PCB mounted buzzer there spar. No expense. This looks like a programming uh header for the MSP 430 and there's nothing on the bottom so I won't bother taking that bought out. but I like it.

it's held him with six. Shake Proof washer. uh, screws there and you can see the zebra uh strips on the bottom there to connect through to the LCD so that's all sandwiched in place I Rather like that design. and yes, they haven't skimped on the shield in here, have they folks? I Mean, look at that.

It's almost completely enclosed except for the Uh penetration for uh, several things. That's the Uh buzzer on the bottom that meets up with the buzzer in there so it just pokes through. And for the Uh range switch, they just holes straight through the mounting holes. Of course, there you go.

But apart from that, it's wow. You know that is pretty well shielded and that looks like classic old school fluke in there. Let's check it out. and these are metal threaded inserts as I said that have captive nuts on the shielding on the other side.

Absolutely beautiful. I Love it, but there we go. Tada We're off. Wow, here we go folks.

This is old school fluke here. Check it out. They've even got the cut out for the main fluke Asic down on there and a classic wafer type switch here. What an absolute classic package folks.

look at that. It's the Fluke 7112 that's their internal part number. This is their Uh Custom Asic which contains a whole bunch of Uh stuff which we can actually have a look at because it uh is inside the manual. but it's the classic flat package.

They haven't formed the Uh leads at all and they haven't got all the leads coming out, the unused leads are just trimmed off and this one's actually it's not like old stock or anything. It looks like it was manufactured 13th week' 04 if that. I Assuming that is a day code, it certainly looks like a classic Uh Dat code there. So they were still manufacturing this Asic in this classic non-lead formed package I Love it! So that aspect of the design I Don't think has changed since this thing was first released.

There you go. We have a recent fairly recent anyway in the scheme of things 1997 date code and there's some high voltage isolation slots in there. They've really gone to town. You can see the little look at the little guard Trace wiggle around there on that device I'm not sure what that is.

it could be a voltage reference, but they've added that little guard Trace in there. They thought they had to do that bit of attention to detail. some Uh classic style, uh, cylindrical, uh, tubular style or whatever the name is for those Uh trimmer caps. There's some more trimmer caps down here.

There's a variable, a couple of variable resistors there, and that is the Uh hybrid. There's the Uh ceramic hybrid there, which would be the Uh resistor voltage divider and these are actually very high voltage withstanding Teflon Uh dialectric capacitors. Hence, because they're high voltage, they're still in the high voltage input uh part of the circuitry, hence the high voltage isolation slot underneath it there. These particular ones are rated to 1700 volts and I Just love the old style radial formed lead resistors there.

They used to use these in the old Flick 70 series way back. If you got an original one of those, crack it open and you'll see uh exactly the same thing I I Love it. They really haven't uh changed much when they updated this thing and that maximum. ICL 7611 That's a ultra low power uh dual opamp and the wafer switch system here is an absolute thing of beauty.

It's got uh, dual wipe contacts as you can see in there top and bottom. Oh man, you don't see these much anymore. That's just wonderful. You couldn't buy that thing if you tried.

and if you want to see that uh fuse Riser board up close there it is. you can see some isolation slots in there. There's some sort of plastic retention clip in the center. uh, which is kind of weird.

And check out we have a little Ferite on that input lead and what that thing's going to do is just take the edge off any um, uh, surge. any input, uh, surges. And when the fuse blows and that device down in there is an IFC 23817 can't find any data on that. Uh, if we looked at the schematic I by the two pin nature of it uh there and the T92 package my get yes and the guard Trace around it.

um, my guess would be that is a voltage reference And here's our milliamp input: Current Shun 4995 Ohms .25% there. It's a biggie, it's a couple of watts and right next to it there you can see the classic Bridge rectifier and doo protection will ensure that the Uh fuse is going to burst and not that big um uh current shunt resistor on the milliamp range in uh, gross overload condition and of course the other limitation of this meter. I Forgot to mention and one thing you won't find on here is a true RMS converter chip. This is not a true RMS voltage meter.

It's only average responding and we've got no less than five Ms here for input. um, fast surge overload protection, but they've got four of them in series here to get the increased voltage and then it would, uh, dissipate the energy across the four devices. Instead of having one big monster one and the black device, there is a PTC the Mis for the slower overload conditions and they've gone to the effort to go. Well, we need some internal shield in as well, so bugger it, Let's put on a big internal right angle metal shield and they haven't skimped there on the battery wires.

Look at that. They've put little crimp connectors on the end first and then soldered the whole lot in. I Love it! Now if you have a look at the tear down of the more modern Uh 28 Series 2 I did you'll see the huge difference in just the construction of the input um, uh, circuitry and the fuses. None of this Riser board stuff I mean this is actually fairly clumsy I mean it's ultimately well engineered in terms of you know, how they've you know, actually assembly of it, but it's just.

you know, it's just a clumsy design I don't necessarily like it from that point of view. The uh, the more modern Fluke 28 Fluke have certainly learned a lot since they uh designed this. I mean but this would have been the same design way back when this Flute 27 first came out and you can see a 105 written in there. and I Do think that uh, my particular unit here is um 25 vintage so it's only 7 years old.

Not that bad at all. Now if we have a look at the schematic here for this main chip, they call it an Ap25. This is the Classic Fluke proprietary Um chipset here which has a whole bunch of stuff in of course it's got the ADC building. It's got active filter, buffer, integrator input uh, Network um selection input.

So it does the auto ranging and all sorts of stuff and you can see the things surrounding it here. Let's have a quick look. there's that um ICL 761 uh, ultra low power Op amp up there with a Jfet. look at that.

love it part of the rain switch here and you can see why this is going to get 1,000 hours battery life because look, it's driven by a 32.768 khz watch crystal. Um I don't know if they multiply that inside, but it's certainly not going to be running very fast at all. I Love it. And uh, there's our voltage reference uh, down there 1.23 volts and then there's a adjustment uh, trim pot there to set that which goes in.

uh, as the voltage reference. we've got some more filter um, some ADC uh, sampling stuff around here and active filter components, buffer integrator components and that. And here's the digital output which goes off to the digital board. As you can see, there's a small data and a dress bus there.

it's only a 4-bit address bus and it's got various other stuff to end of conversions and clocks and all sorts of things which go off to the Um MSP 430 processor board which gets the data out of this thing and displays it. and it even gives you a little uh description here of what's inside this custom analog IC And as you can see here it says that U1 also contains digital circuitry for the state machine control over the ad decoding. ROM So it's it's got internal decoding ROMs and state machines in there which allows it to do all the auto ranging and the analog to digital converter. And it tells you the Ad conversion is accomplished using a modified dual slope.

Uh. The conversion method method Uh can be described as a charge coupled multiple slope technique. A series of 10 minor conversions occur every 40 milliseconds each at one10 the desired resolution without taking time for an auto zero phase between conversion. The these minor conversions or samples as they are called in the following discussion occur at a rate of 25 per second.

Hence, uh, that's why they can get the fast response on the bar graph display at lower resolution compared to the screen. so new new samples are taken every 40 milliseconds. 10 samples are summed to produce a full resolution digital display for the 3,200 counts. There you go.

So that is the basic operation. Here we go if we zoom out here that there is the basic oper operation of the ADC and the state machine I Love it! And that's all inside that custom fluke Asic which they've had for many, many decades and no doubt they have a patent on. and if we have a look at some of the specs here, you can just see how awesome these are. For a 3200 count multimeter, I mean 0.1% plus one count on DC volts it drops to 2% plus one counts on the Oh Ohms range.

it gets higher. Outside of that, of course it's still .2% on the conductance Range there plus 10 counts. Of course Di only goes to 2 Vols and the AC's you know, not the best of course. Um, but that's all right.

And the current, uh, where's the DC current? It's not that spectacular at 75% plus two. But the basically the Ohms and Volts are excellent specs for a Uh three for basic, a three and a half digigit multimeter. and if you have a look at the specs here, of course it's designed to survive almost anything. It's uh, waterproof to 1 meter down here.

it's uh, shock and vibration and water resistant oil waterproof the whole thing thh hour battery life. It's absolutely massive. um and it's designed to operate uh Cont: temporarily operate down to -40 C for 20 minutes I Love it. So there you have it.

That is the new model I guess you could call it uh. original Fluke 27 the yellow and charcoal one as opposed to the original design which you would have seen which you would see if you take it apart would not have of course the new Um TI MSP 430 processor in there to drive the display. So this is an interesting mix. This meter of uh, you know, modern sort of.

You know a they've retrofitted an old design. They kept a lot of stuff the same I mean the classic Asic on the bottom there. They were still able to manufacture that, so they're still using it way up to 2005 and and presumably well beyond that right up until they, uh, discontinued this model. and it's basically the classic design which you Pro and the wafer uh range switch here is probably exactly the same design they used in the original one.

and uh, you know, the vertical uh, radial resistors there? Absolutely classic design, interesting blend of old and new. So um, if you want to pick up one of these uh, Fluke 27s which I highly recommend you do. If you can get one, uh, cheaply, do try and get the yellow and charcoal one the more modern one because it's going to last you a lot longer purely because it's not, well, you know, 20 years old or something like that. But uh, by all means, um, pick up the older model as well cuz they as long as it's uh, still in good Nick and the screen is, um, still working well and hasn't faded or anything like that.

Do pick one up cuz these are an incredibly robust and very accurate and very reliable basic 3200 count, 3 half digigit multimeter. But just do be careful what you pay for one of these things. I Paid 40 bucks for this in practically brand new condition so you know I I think I got a pretty good fine, but there's still some people selling these for a couple of hundred bucks, you know, So they they do tend to hold their value quite well, but you I have bought a few of these in the past at very rock bottom prices. so if you just keep your uh ears to the ground, you might be able to pick up one of these puppies.

I Highly recommend it if you don't mind the uh size and the weight of course and the lack of uh some F functionality get on more modern meters. It really is a good reliable meter to have. Highly recommend it. So if you want to discuss it, jump on over to the Evev blog uh forum And as always, if you like these sort of tear downs and multimeter stuff, please give it a big thumbs up.

Catch you next time! m.