A multimeter without any screws? A 1990's vintage Metrix MX44 multimeter torn down, tested and calibration adjusted.
Tektronix Multimeter Repair-o-thon
If you find my videos useful you may consider supporting the EEVblog on Patreon: http://www.patreon.com/eevblog
Or with crypto:
Web Site: http://www.eevblog.com
#ElectronicsCreators #Teardown #Calibration
Tektronix Multimeter Repair-o-thon
If you find my videos useful you may consider supporting the EEVblog on Patreon: http://www.patreon.com/eevblog
Or with crypto:
Web Site: http://www.eevblog.com
#ElectronicsCreators #Teardown #Calibration
Hi! it's another video from the mystery box of multimeters from the bunker and this one's really interesting. It's the It Instruments Meex Mx44 now. I Used to lust after these Metrex meters when I was a kid. You know you look through the magazines, you see the ads for this amazing looking.
This is not the most amazing looking uh one, but they had like a 50 Series as well that had no less than 10 buttons up here. But I think the late ' 80s, probably early '90s where these stem from. If you know the exact date, well, we're going to do a tear down, but I lusted after this thing. It seemed like it was the most feature-packed meter on the market and it was like IP 66 uh, waterproof or water resistant.
and it had this patented securex interface here where uh, you couldn't physically open the thing if the test leads were plugged in. so this was like a safety uh thing. So thanks to whoever sent this into the mailbag, I have not torn it down yet I just uh, opened it to put in a new battery to make sure it works. and sure enough, it does, actually, um, work.
it's actually fully operational and it's a little bit out of spec. This one's only uh, 4,000 count hence the 40. I think the 50 Series that was either 5,000 count or 50,000 uh count meter. Uh, please correct me in the comments.
I'm going all by memory here and um, this one yet not particular accurate. So 4,000 count meter uh with. 2% accuracy or something like that if I can find the specs I'll put them up here but I had to SP fast responding bar graph on it. let's actually try that shall we? Whoa yeah like you know it was 20 times a second or whatever and it also had in memory mode.
Yeah it. it continues to update the bar graph after you've frozen the screen like this and it had like bar graph Center zero modes and it did and it had a bar graph Zoom expans mode. This particular model doesn't have it, but you know it had all sorts of fancy stuff in it at the time which was all all pretty. Advanced and yeah, the fact that it was waterproof and rugged and they touted that it met all the new standards and things like this.
Now Metrix is still around. You can still buy Metrix multimeters. uh, it's they're from a brand of the French company Chauvin Unur if I'm pronouncing that correctly. Um, but they don't I Don't believe that they sell this particular Um form factor anymore.
so I'm not sure how it instruments, uh, go into it because um, Mx40 the Metrix. If you look at the old Uh manuals for these things, they're the French they're from France so I whereas ITT is an American company. so I'm not sure of the history there. So if you do know, uh, the exact history of all of that, um, please leave it in the uh comments down below like there's no made in France on here.
So I don't know if you I presume that they were made in France but I'm not exactly sure. Leave it in the comments if you know. Anyway, one of the most interesting things about this is that it's a multimeter without screws. How do you? Where's the battery compartment? No, trust me. take off those feet. There's no screws under the feet and this one's missing. It's tilting. Bale So I don't think the tilting Bale was big.
It probably only went up like a small amount. Where's Wally Where's the screws? How do you get access to them? Well, it's to do with as I said this securex thing. So what you do is you actually this actually snaps off like this. Okay, and this actually prevents you take, um, getting access inside and replacing the batteries and fuses with the leads plugged in.
CU Obviously, if this is on and you've plugged the leads in, you can't get this off. And if you can't get this off, this actual front panel here is the thing that lifts off and you get access to the battery compartment. So isn't that groovy? I Mean, after all these years, right? it? it still Clips on Just fine. So it's so all the Plastics are really top quality and everything else.
and there's your interface and this. You actually take off here and this whole front cover lifts off. So let's give it a go. There you go, it is actually a bit hard I Can't do it with my plastic spudger.
Um, it's so this one's a little bit stiff. but check it out. Tada There we go. So I've got access to our waterproof battery and fuse compartment isn't that isn't that at the duck's guts? Look at that.
I mean HRC fuses of course and I love the uh, the clip holders in there. So we've got the big Jobby in there for the 10 amps of course only the smaller M203 in there for the uh, but that is a HRC and you can get in there and there's no room for spare uh, fuses in there unfortunately. and I Love the battery holder in here. Like it.
just. it's just all very nice indeed. But where's the screws? I've taken one of the feed off and there's 's no screw under there and my white balance is way off here. By the way, this is actually orange.
It looks yellow. or at least on my screen here it's not really fluke yellow. it's or maybe it's changed color I don't know for those cuz that is a little bit different to this. so I'd say that's more the original color in there.
There we go, looks like we can get that off. These are really tight. I Can't use a plastic spudger for this. Tada and look at this waterproof in again.
Beautiful by Desla. Wow, look at that. There's two screw holes. um but there ain't any screws in the top.
not feeling anything under there? yeah see there's nothing under the foot there that just H Clips in there like that. So I presume? um it's all clip around here cuz meex seem to have like the clip thing really down pat. so I probably no surprise that the case is also uh, clip cuz you should never have to open the case of course. I don't know if it's electronic calibration or whether it's uh, trimmers in there, but they sold these for D like decades. Um, you could buy these Metrix meters and there's lots of different models that were sold under different brand names. Robin I think was one of them and other various brand names so they'd actually uh re you know they'd OEM them. Lots of different Uh models with different range configurations and stuff like that, but the same async. Advanced Safety concept and uh, securex um interface? um was around for a long, long time.
If you know the exact dates, please leave it in the comments down below. but yeah, I I just absolutely lusted after this. I thought this was a dark scar. um, like waterproof? you can get uh, the Mx50 7 ex which was the intrinsically safe uh version of it as well and they would have sold very well into the industrial and Mining markets and stuff like that.
This particular one is from. uh Transfield um which is like the Rollways is here in Australia I think I think it's the railways here in Australia Um, so yeah, this would have been used out in the field. Um, just by the looks of it, it's oh grubby. Yeah.
Yep, yeah. Okay, so there's something happening there. Unfortunately, the plastic spudger doesn't doesn't really do it. I think I'm going to have to get medieval on its ass and really get metal spudger uh, screwdriver knife in there and I'll get back to you you.
you probably don't want to see this on camera. It's traumatic. Oh, there we go. We got it.
Yeah, yeah, there's a okay so you had to know where the big where the big clip was. It's up. it's up. It's up the top there, all right.
I I Didn't do any damage so it was clipped together as suspected. Yeah, the plastic spudger was never going to do that. Here we go. Oh and we got seal again.
Look at this. Oh beautiful. So yeah, that was serious about waterproof in this thing. Um I the knob will have something.
probably have something on the front as well, but quite a bit of through hole stuff in here. and uh I'm liking the interface here so they're not. uh, they're not Shake proof washers. so I presume they've got some Loctite on those, but uh, they look pretty beefy.
Yeah, straight onto the PCB though and it looks like there's your buzzer. Uh um, so rain switches probably held in with those four there, it should just should just pop out. This could be the LCD screw. I don't think that's holding.
oh could be holding down the board I think maybe maybe these two here. Yeah, they look like they go into the plastic H case. yeah, that's that's lifting out. I'm pretty sure that's for the rain switch.
I may actually have to take out the connectors I think who? yeah, they were tight as a nun's nasty. Wow. but no. but no lock tight.
Oh wow. I'm really struggling to get those. This small diamet up screwdriver is really not. Oh yeah, they are tight.
Yep. I can feel it coming. That's what she said. Let's go there. We go. Come on, you can do it. So it's interesting that the Jacks aren't that are they're integrated to the case. I'm pretty sure I don't have to get those out I'm pretty sure they're holding the range switch mechanism on the top.
There you go. Just needed a bit more persuasion. I think this is really complex fit and I'm quite impressed. Yeah I lift up one side and I think the key is to get one side up and then lift the other.
Maybe. Oh, the fuse. the fuse. You're probably screaming at me Dave you dumbass take the fuses out the fuse cuz it had that had that plastic on the bottom.
whereas that fuse didn't. this fuse did do there. We go. All right.
Beautiful. So there you go. The switch mechanisms are sealed fantastic because you know you want your waterproof in and stuff so we won't get that apart. I assume they've got like a maybe you know some o-ring in there or something.
but check out check out the Jacks they are they are molded into there that is. that is really something that it's nice attention to detail there. I'm very impressed so let's flip it over. We got two board construction and the switch is on that top board there.
that's very nice and they've got this nice it's it's foam but that that would be part of the waterproof in too because the plastic case would seal against that. so that's like wow So even if water did get into that battery compart fuse compartment it's it's not going to get into the PCB Very impressive. They definitely have a different board. uh for the different models cuz like you know the extra buttons aren't there.
um so as I said, they have up to 10 buttons I I I don't know if that's on the 40 series I Don't think so cuz I think the this 44 might have been the don't know if it's the top of the range of the 40 series but anyway there's our 10m input resistor there. oh we got another one over there as well. That's a Nmeg jobby now. This is quite an old model.
sort of like before the standards, so so we got one. PTC There doesn't look particularly grunty. We have to take this top board off, don't we? So that rain switch is held in there with standoffs? It's very nice. I wonder if it's like two sided cuz obvious.
Oh, nice. metal threaded inserts? Lovely. Oh, everything in here is metal threaded inserts except the Bo. except those two screws that held the board in.
They went into those plastic studs over here. but that's all right. And this plastic. ah, it's built like a brick Dny.
It's like really top quality stuff. Markings on it for you tooling fish andad doesn't seem to and we got shield in on the bottom of course. Aha. we have a date code.
just noticed that 95 so mid 90s here. But yeah, as I said, I'm pretty sure these were around in the late 80s Metrix meters I'm sure. I Remember the ads from the late 80s? That's just a alignment hole. Is it? Is it a stud? Does it come out? Yeah, yeah, it. It's a little. It's a little clip. A little slot clip that obviously holds it in position and stops it from. ah so that.
make sure it's in the correct orientation when you assemble the thing. That's got to be it. That's got to be for production assembly to make sure the switch is correctly aligned. It's beautiful.
anyway. Flipping Doah! And yeah, we just got a couple on this side here and we got an NEC Jobby over here for driving the LCD So um, 77503 Um, oh no. DMM 10B Is that the multimeter chipset? Anyway, 13th week 94 day code. This would have been your multimeter chipset down here.
It's it branded. So I wonder who actually manufactured this 9318 So obviously this is a custom Asic I assume custom Asic which they've developed. Oh, there actually a fair bit of protection in here. We got three.
Ms it just wasn't all down on the bottom like I expected. And as I said, there's the high voltage 10m ceramic jobby. And then we got another high voltage nmeg ceramic jobby there. Yes, So much for the electronic calibration.
We got three trim pots there. how do you trim those after the fact trims them cuz you can't access those trimmers. Uh, once you've got this thing on anyway. 760 voltage inverter there and a 7611.
what is that off hand? I don't recall I Put up the data sheet for that little Shield there over two resistors. Okay, they're important for some reason. so attention to detail. We got guard traces the exposed guard.
Okay, so yeah, that's a sense. You can tell you know sensitive node. Okay, sensitive node you don't want any leakage on because they got the exposed guard traces around there and they're exposed so that um, if you get moisture on the board then it can actually make electrical contact with the guard traces there. so they've left those exposed and that's okay.
Yeah, there you go. That is the 10m import. so coming in and they've got a shield around that. Nice, nice attention to detail I Really love it, but this is pretty minimalistic is it not? I Mean this is not a true Rmsr converter I Don't believe.
Looks like we got our Diode Bridge there protection for the 10 amp current Jack And where's the current sense resistor for the milliamp range? Not seeing it? Yeah, three T Trimmers. Is that the reference up there? That 92 Jobby C1959 don't know transistor I Don't think that's A and we got a tag tent. What evil tag tants. This thing still works.
It reads a little bit High I think it reads consistently like not sure. Is it 1% High I think on all ranges, but yeah, they've just developed their custom Asic I wonder how long they used that for I Wonder if that sort of like spilled over into the 50 Series and the higher end models I Don't know if anyone's got tear down photos of the higher end 50. Series Please leave it in the com Link In the comments down below, we got four Ms, one PTC and one, uh, high voltage. Is that a fusible jobby? Another T92 in there? What is that? A double, two, double? Two For The Win Classic. Try that one. They've glued down the fourm crystal there. So yeah, look at that. I mean you know, old school 80s 90s multimeter design, but done, You know perfectly.
Pretty much like like, can you fault this I can't fault this. This is just really very nice indeed. Just a couple of little extra rangy things up. oh that that' be power that would just be getting power through would it? Cuz they've got the power ring going around there and it's not doing any measurement? uh.
switching? That's all done on the other side. I Almost don't want to take that off Should I people are going to if I don't? Yeah, look at metal threaded inserts for your range switch. That's just beautiful thing of beauty. Joy Forever Behold, the Won Mobile thing of beauty is a joy.
forever places please. The dance is about to begin. Okay, let's lift that up and don't It looks like it's It's totally symmetrical so I could No. I can't put it in either way.
check out the alignment post there and there. So yeah, you definitely can't get this wrong. That's fantastic. And it's You know, pretty simplistic switching in this thing, but you know they do separate it.
It would be more if it would look more complex if you only had this singles sided. Uh Jobby. But yeah, it looks like they've got an alternative resistor footprint in there for the current shunt, have they? So we we didn't find them. Oh oh, is that the current sense resistor for the milliamp shunt? I Think it is.
Aha, there's your reference. All the Lm358 Fanboys go wild. Um yeah. 2 and half volt reference.
Uh what? That's the Zed I don't know what temperature class that is? Um, but yeah. like as I said, this is like a. 2% class meter or something. It's only 4,000 count.
it's not. it's not, you know. 4 and a half digit Point As I said the 50 Series that can. that at least got down to 0.025% accuracy spec.
so you know. Pretty groovy. yeah. So I'd love to recalibrate this thing.
CU As I said, it's significantly out like consistently on all ranges. main reference is obviously drifted or the main calibration of the references obviously drifted to impact. All ranges consistently little bit high. but like I said, I can't see how I can actually get in there and adjust those with the LCD on.
Um, there's no ho. like there's no oh no bottom access hole. There you go. Bottom access I Was going to say there's no bottom access hole there is.
didn't look duh. So I will attempt to recalibrate this thing. We'll have a go shall we? cuz it's worth bringing this thing back to life. Maybe I can, uh, auction this one off as well.
At the end of this video, I've been oxy auctioning 4 M lately those Tectronics Jobbies still works still a Bobby desler. So what I'll do is I'll put this as a main Channel video and if you haven't seen it um I did a followup video to the tectronics uh, repair one I actually repaired three more repaired as you'll see in the video, repaired three more Tectronics meters and they're currently on eBay uh for auction as well starting at 99. although I think it's gone way above that. So yes, if you're not subscribe to Eev blog 2 you're missing a ton of stuff like I do put random stuff on there like you know I'm I'm installing a pool at the moment. you know there's pool installation video. There's other random stuff, but there is stuff that you think might be on the main. Channel Please leave it in the comments down below if you think some of the stuff on my you know should EV blog 2 just be for personal stuff or should you know I just should I put everything on Main EV like everything electronically related? should it go on the main? Channel I don't know, leave it in the comments down below. but I like this I Like the fact that I can just now got the access hole there to um I don't know which trim is what? maybe I can find a calibration manual otherwise I'm going to be just Murphy will guarantee I get the wrong uh trimmer hole here but yeah, I can I can put this together and I can uh trim this I can calibrate it so with the with the back off this is great I Love this design.
seem to know what the heck they're doing with um you know, like these you sure surely these would have all uh like failed over the years. like just G more like all brittle and everything. but they seem to have designed them well and the plastic seem to be super high quality in this thing to last all this time with just plastic case together. the multimeter with no screws.
that could be the title of this video. what's a Seest brand? Never heard of it. leave it in the comments. so I hook it up to my lab reference here: I got a set to 100 m Vol And of course my MV 106 here has gone to a standards lab and uh, been compared and yeah, it's good enough to calibrate like a 6 and a half digit meter let alone a uh 4,000 count meter like this one.
So 1.1% out. so yeah, that's out of spec. so and uh, we can change the various ranges as well. So that's the Molt range and DC um it's exactly the same.
like bang on to the least significant digit. It's also 1.1% out for the 10vt range and uh, that's the same for the Ohms as well and I believe for the current as well. So it looks like one of those trimmers is going to be the absolute uh, tweaking. but I don't know which one.
All right. So this one here is next to the voltage reference physically next to the voltage reference. So going to give that one a go? Got the screwdriver that fits. Oh hey, hello, she she is.
she's turning there we go. look at that. Oh, hold tongue at the right angle. Hang on. Can't talk with her tongue at the right angle. Oh no, no, just the act of pulling it back out caused a problem. That's what she said. Okay, come on, you can do it there.
We go there, We go there, we go. Oh, come on, did it again. I'm calling it I'm not not going to try and tweak it any more than that. That's good enough for Australia There you go and we'll find that all the others.
So if we go down to one volt, that'll be bang on as well. find that the 100 Molt is close as well. But oh that's no, that's not good enough for a Stralia. I'm going to tweak it to aact you that a look look look 100 MTS don't don't breathe on it 10 volts.
Oh look at that Bobby Desler Bang on. Fantastic! I Wonder if the Oh skis come good? All right. Hook up my 10K reference and that's out as well. So obviously that is not the same trimmer.
So I'm going to guess this one over here which is part of the input divider. So I'm going to give that a Tweaky tweak and hopefully that is a different. Yep, there you go go. and tongue at the right angle? Look at that.
10K That's good. No, it's not good enough. There we go: 9.99 10K There we go. Fantastic! And sure enough, that has not marked up the voltage calibration.
Brilliant. Do just occurred to me that I should have done that near full scale. 3.99 or cuz this is 40,000 count. Is it not? No, it's like 32,000 Is it 3? 6? 3.7 3.8 3.9 Oh 3.99 jumps up.
It can't quite do the 4,000 I'll tell you what this trimmer is so on the edge. No, it's almost like it has to go to that position due to like, like a little indent on the on the carbon trimmer or whatever. I can't actually get it under like slightly under that if I do it like un undoes if you know what I mean. So there you go.
Uh, 1.5 Anyway, it's measuring 1.0 precisely. So yeah, that's the problem with these carbon trimmer resistors like the single turn jobbies, right you? You just got no range there to like to tweak the thing like you just I like put the lightest pressure on it and it jumps like a couple of digits either side. So there's natural places where the wiper makes contact with the carbon trace on the trimmer and you know there's only so much you can do. Um, depends on how they've designed the the window range for that trimmer.
But anyway. I it's bang on SL Like two digits off at three. it's two digits off at three volts. I mean oh, but I can't get it right to three.
It's just annoying. Anyway, that is definitely good enough. A strier? Um, let's try the AC volts now. Okay, AC Volt is standard.
It's a little smidgen off there. Well, let's try that third trimmer there. Yep, Yep. Yep.
go the other direction. Yep, Yep. Okay, so I'm currently feeding in 10 volts Ac. Oh, and trim it down a little bit now.
Unfortunately, my metal trimmer seems to be a problem there. so oops. So I use a paper towel cuz it's obviously picking up my 50 HZ there from my oh from me. tweak it back, tweak it back, tweak it back. Come on. 10 10? Look at that. Ah look. I bought one 30 volts there.
very close. 3 volts. Oh, look at that. bang on.
Yep. Okay, AC is set. So we've done all three of those trimmers. so we're talking uh DC Volts? uh, reference over here.
We're talking the resistance adjustment here and AC volts Over here. there are our three trimmers. So everything else. um, you know, like current and everything that'll be uh your DC Um, that should be fine and dandy.
So look at that. it's bang on 29.8 five. It's a bit low, but little bit disappointing there, but there are no more adjustments to be made unfortunately. Oh no, now it's reading 298.
So I don't know Is my standard a bit off here? Let me try my reference key site. Yeah, that's definitely out. Um, has it moved since I physically moved it from the bench? Let me go put it back on the MV 106. Yeah, see, it's moved again.
a bugger. Okay, well there we go. That's the nearest I can get it to 300. let's go uper range and 3 volts.
There we go. We're back on back on track. All right, let's take it back over to the to the other bench. There we go.
Now we're talking. Yeah, there we go. look at that. 300 Ms All right.
So the current should now work. Let's try it. Aha, now we're good. There you go.
30 milliamps. That's fine H that's reading volts up there. Don't worry about that. This is more than good enough by the way for calibrating a 4,000 count meter.
Um, so yeah. okay, no worries. this will only go up to 110 milliamp, but looks bang on I need the power supply for that. We'll just rely on the road and Schwarz up here.
But yeah, 2.96 So yeah it's It's good enough so you can see why manufacturers moved away from those carbon trimmer resistors to software calibration. It's just. it's just way better that is. A look inside this Metrix: uh ITT Instruments MX 44 multimer and as I said I Love lusted after one of these bad boys and leave it in the comments down below.
you're still using one If you got a soft spot for the Metrix uh meters, you can still buy the Metrix uh brand and the uh Asic um safety thing. they're up to like version four of that and you know the secure s Jacks and the screw free design of this thing. apart from the two screws that hold the PCB in. but you can open up the entire case, it's all held together all without screws and you can open up the meter case without screws and the tilting bail on here you you actually take it out and um, it's it uses as a lever to open up the front cover here to access your battery infusers.
Fantastic 500 hours battery life I Do believe so you know. not too shabby at all anyway. I Will uh, put that on eBay Starting at 99 C Auction I Will link that in down below and if you like that video, please give it a big thumbs up. And as always, discuss down below or over on the Eev blog. Forum Catch you next time.