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Amarbir,
Take a look at the third post in the thread. -
Amarbir,
Take a look at the third post in the thread.
Well,
checked .Now This Is What Dave And The Mods Should Be Looking Into .They Do Not Have a Image Resizer Mod / Addon Installed Into Forum .You Do One thing Register on My Forum And Have a Peek At that Post again .You Will See What i Am Talking About .We Should All Collectively Request Dave To Implement a Image Auto Resizer. -
Thanks for another great teardown and mini review.
PS. I prefer pictures as thumbnails and then I can choose what to expand for a bigger picture. -
Thanks for another great teardown and mini review.
PS. I prefer pictures as thumbnails and then I can choose what to expand for a bigger picture.
Well ,
Bro if he has this mod installed ,then he can select a default size to appear in posts .Once that is set you will see all small images in posts .Then you click on anyone and it will expand in a zoom manner .He should do this IMHO -
Really nice to see this teardown and review. I have enjoyed my 5360 for about 10 years and I really like it.
Recently I made a little RS-232 interface from an IR led, a phototransistor, a couple of resistors, and a $2 USB-to-RS232 adapter from eBay (search for PL2303HX). You can determine which of the two IR devices is the transmitter by watching through a digital camera and pressing PRINT. The serial settings are 2400/8/N/1.
You can get a single reading as ASCII text including units by pressing PRINT. You can get one reading per X second by pressing and holding PRINT (and configure number of seconds between readings). The basic RS-232 interface spec is documented in this: www.snesometel.com.tn/images/PDF/NF-SX-ASYC2.pdf but it does not include the special calibration commands.
The calibration software (AK5350) is discontinued and is now freely downloadable from the B&K website at www.bkprecision.com/downloads/software/AK5350.zip but you need to be able to run 16-bit Windows programs (i.e. won't run on x64 versions of Windows). It works perfectly under XP and using the simple USB serial adapter I described above. -
macboy,
Thanks for the great additional information. I wish they had setup a more accessible IR location with this meter. The need to sell a new battery 'door' just so you can use the IR stuff seems really dumb. Still, the few times I will data log I don't think high voltages will be an issue. As I have access to a 3D printer I might make a cable per your link.
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Recently I made a little RS-232 interface from an IR led, a phototransistor, a couple of resistors, and a $2 USB-to-RS232 adapter from eBay (search for PL2303HX).
Got a picture of your homemade cable? I'm interesting in possibly building one. -
The circuit for the IR I/F is very simple. TTL level serial is active low, so on the transmit, you connect an IR LED and current limiting resistor in series between the +3.3 V and the TX pin. On the receive side, an IR phototransistor is used to pull the RX pin low. The USB-serial adapater can be found on eBay from Asian sellers for $2 or less. Search ebay for PL2303. In an earlier post in this thread you will find links to a manual with the serial protocol for these meters, and link to calibration software from BK.
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Found one of these in the WEEE bin at uni, fully functional, not sure why someone would ch8ck such a nice meter. Sadly when testing the current on my new meter the cheap PSU could not take it and died, the fuse in the PSU exploded and the power trans have probably shorted. Oh well I will just have to fix it again.
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Found one of these in the WEEE bin at uni, fully functional, not sure why someone would ch8ck such a nice meter.
Good score for free. 
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Thanks Robomeds for this post !
I am French and boy I struggled to tear my MX 55 apart... it took a chap from the other end of the world to tell me how to open "our" meters ! LOL So thank you for detailing the procedure to put it to bits. Armed with this, I will make a new attempt at open it !
I agree with everything you said : great meter overall, I just love it and always wanted one when they were new 20/25 years ago and I was just a kid dreaming as I saw them tested in the electronic magazines of that day ! They were worth about a month of salary IIRC.
As for the history part, I read some thins wrong above, so I would like to correct.
It's easy to get lost because Metrix's life has been such a roller coaster throughout the years ! One day merging with similar companies to form a group, another day getting bought by a group or part of a group, then sold again to XYZ ! Hard to follow.
But to put things simply :
Chauvin-Arnoux and Metrix are both very old big French names in the instruments business, alwyas have pionnered the market, alwyas designed their stuff in house of course, and still do taody ! Their R&D centers are still in France.
Chauvin-Arnoux was formed as far back as 1893, and Metrix in 1936, first famous for they vacuum tube test gear, as it was the technology of that era.
The two were then competitors, Chauvin-Arnoux always wanting to buy Metrix... which they eventually did later.
As for the ITT thing :
In 1964, Metrix got "affiliated" to ITT, nothing more.
In 1970, Metrix merged with a few subsidiaries owned by ITT, to form a group.
In 1979, the Metric products were rebranded " ITT Metrix "
In 1990, Metrix was the leading manufacturer in the whole of Europe, for analogue and digital multimeters.
In 1994, and of the ITT affiliation : Metrix got sold to a group of companies (mostly French and German).
... which had overambitious plans for Metrix, 3 years later, the group, and Metrix with it, bankrupted.
... that leads us then to 1997. This were Chauvin-Arnoux offered to buy Metrix, the judge in charge accepted... at long last chauvin(arnoux managed to buy his competitor Metrix !
The two French big names are now united in the same group. Chauvin-Arnoux was/is clever enough to let Metrix design and build their own stuff, sold under their own Metrix brand, so nothing has changed. Metrix is still Metrix... except it's now out of trouble financially because Chauvin-Arnoux owns them.
So basically, it wall started a century ago with Chauvin-Arnoud, and a century later, after troubled times, it all ends with the same two brothers ! Except they are now joining forces, instead of competing against one another.
Here is a link to a PDF emanating from Metric, that describes the whole story, written in French obviously sorry, but I highlighted the main points above.
http://www.geode-annecylevieux.org/____assets/uploads/2012/01/METRIX.pdf
As for the chip driving the MX 50 series, I don't know its story. Obviously Metrix were not big enough to have their own manufacturing plant, so maybe they designed the chip in -house and just asked ITT to manufacture it for them... or did ITT already have this chip in their catalog and let Metrix use it to roll their MX50's around it.. or was it a joined effort / co-development, shared between ITT and Metrix... who knows really, not that it matters in the end... the result is a great meter ! :-D
As for BK et AEMC of who ever else, it was obiously just a rebadged Metrix.
Anyway, sorry for the length... I came here as well to ask Robomed or anybody else... if there is a schematics or service manual available somewhere for the MX 50s series ?
.. because my MX 55, which is externally/cosmetically in like new.. must have something wrong deep down, as it acts weird and funny and pretty much every function but the current measurements. I suspect most of the weirdness might be a problem with the input protection circuitry, but there is one misbehavior which I fear might not be as easy to diagnose : in the mV range, it screams at constantly. The "high-voltage"/danger alarm and icons, come on as soon as I set the switch/knob to the mV range, even though the test lead are not connected to anything. shorting the leads makes the alarm go off.
Anyway... would be great if I could have a schematic for this baby, to help me trouble-shoot the thing... because I just love this meter and although it is extremely sick at the moment, I will not give up on it without a good fight !
No idea what kind of abuse the meter might have experienced to show so many problems... it was already like this when I bought it used, 3 years ago... the seller never mentioned anything about any kind of problem.... that's honesty for you ! :-/
Oh, before I go, for those interested, I attached a couple PDF files below. Commercial leaflets of the day, presenting the MX 53/4/5/6 series (in English) and another leaflet (in French) presenting the later/revised ' C ' version of this range of meters.
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must have something wrong deep down, as it acts weird and funny and pretty much every function but the current measurements. I suspect most of the weirdness might be a problem with the input protection circuitry,
Some questions.
Q1) If you measure an AA 1.5V cell, what does your meter show?
Q2) If you short out the probes with the meter in DCV mode, what does your meter show?
Q3) If you measure a 1k ohm resistor, what does your meter show?
Q4) If you short out the probes with the meter in ohms mode, what does your meter show?
Q5) Can you post clear focused pictures of your pcb, both sides?Quotebut there is one misbehavior which I fear might not be as easy to diagnose : in the mV range, it screams at constantly. The "high-voltage"/danger alarm and icons, come on as soon as I set the switch/knob to the mV range, even though the test lead are not connected to anything. shorting the leads makes the alarm go off.
Another member, modemhead, now has Robomed's BK 5390. He can verify the above. -
Using Robomed's photo,
Q6) RV1, RV2, RV3 and RV4 are your MOVs or varistors. With another working meter, each should measure open circuit in ohms mode. You can measure "in circuit". Report your readings.
Q7) R2 is a PTC, thermistor. It should read anywhere between 500 and 1500 ohms. You can measure "in circuit". Report your reading.
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Away from home at the moment, but when I get back in a couple days I'll get out the 56 and see if I can learn enough about it to say something smart.
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Vince, thanks for the reply! Honestly, posts like yours make it worth the effort. I'm glad I checked the forum when I did. I've been all but off the web for 2-3 weeks now due to the real world. Kind of nice to see this and reply same day.
I'm certainly looking forward to any comments/thoughts from those who replied to you already. That's a good brain trust. -
Hi all, and thanks for the replies.
I am bit late in replying, because well, I spent the entire week-end working on the Metrix ! Friday night I actually did not sleep at all, I was up all night and morning at the bench !
So, I tested it as well and as thoroughly as I could, given my limited/modest equipment. But with the help of a little creativity, I managed to achieve more than I first thought was doable... My other/working multimeter, the only one I have, is a trusty 20 year old Fluke 11, which I bought new back in the day. Horrendous 0.9% accuracy (but much better in practice/reality, probably because despite it's advertised crappy accuracy, it DOES have a hybrid ceramic network !) and cannot measure currents. But at least it can go down to a one mV resolution, and measures ohms and capacitance. Then using a breadboard and lab power supply, I was able to wire up some simple test circuits to check the mV range and mA/uA range. I used the current limiting adjustment of the power supply, to test the main 10A current range. It doesn't have a digital display, only galvanometer, so not very accurate, but still useful as we will see further down. main DV Volts I cold test up to 60Volts by putting the two outputs of the power supply in series.
So, what works in the end ? Most of it.
- Diode test
- Continuity test, though scratchy but well if it's not latched what can you do.
- Frequency measurement. Quite sensitive : even with the probes in free air, it picked up the mains zand displayed a rock solid "50.00Hz".
- Ohms
- Vdc
- mA/uA : works.
- mVdc works
- Capacitance
So, what are the remaining problems ?
1) Capacitance range : when you first select it, it shows, as expected, a steady 00.00 nF, with the occasionnal "00.01" LSD poping up erratically, I guess this is OK. What is not OK in my view however, is that if I measure a capacitor (or just short the leads, making it believe it's a massive/out of range capacitor), AFTER I have measured it, and the leads in free air then, not connected to anything, then from this point on, the display is NOT a solid 00.00nF as it was before and is it should be. Instead, the last 2 digits (00.XX nF) are floating and dancing quite a bit, like if there was some capacitive effect at play inside the meter, following the measurement, that would not go away.
2) the main 10A current range : I took a few data points from 0?7A up to about 2.5A, which is what I can achieve with the current limiting know of my power supply. Data points show that the met basically reads about 40% higher than it should ! Yes, quite a lot indeed...
For reference, the data points where : 1,4A read instead of 1A, then 2.1A instead of 1.5, then 2.8A instead of 2, then 3.5A instead 2.5 and lastly 3.9A for about 2.7A on the galvanometer, which was the maximum the power supply deliver.
So it seems like a (huge) calibration error ? Seems crazy to be THAT off, even without calibration ? But well... what else. The Cal as usual help in an external serial EEPROM, and these are usually rated for 10 years right ? Meter is around 20 years old... so why not. Thanks to "Macboy" in his comments further up, it seems the calibration software is luckily freely available, and that the serial cable to connect to the IR ports on the meter's main board, is not that big a deal to construct, and that even the protocol is documented ! What more could I dream for ? So I guess I will have to take this path.
3) The mV range and the dreaded alarm... spent quite some time fiddling with the thing, trying to understand what was going on, and chasing a few red herrings in the process ! The alarm does not trigger when you short the probes, or if you actually measure a voltage. But it will trigger invariable if I touch a metallic part with one of the probes (the other probe remaining in free air). Work every time if I touched the ground/earth/chassis connection of the power supply, or the ground/outside part of the BNC sockets on my scopes or function gen. Works also if I touch the tip of my soldering iron (be it plugged in or not, makes little difference). At some point, I didn't even have to touch anything ! I mean... I noticed that once, the simple fact of APPROACHING one of the test leads to the tip of the iron, was enough to make the Metrix go nuts ! I would see the mV readings on the display, go up and up as I was progressively approaching the probe to the iron. The Metrix saw 500mV, and hence the alarm would trigger... and this happened when the probe was about 4 Inches / 10cm away from the iron ! Crazy. So yes, as I said, the alarm is not the "high voltage/danger" as I though initially, but instead it's the overload/out of range alarm, indicating that the meter sees more than the allowed 500mV on its inputs.
I noticed that that if I select the "AC + DC" feature on the mV range, it becomes even more sensitive ! in mV dc, when disconnected, the meter would read something reasonable, a few millvots, but if you set to AC+ DC, then it reads HUNDREDS of mV right from eh start ! So it's already very near the 500mV trigger point of the alarm, meaning it doesn't take much at atl to trigger it.
So there is something wrong going on here for sure, but what ?..... Why does it read hundreds of millivotts when unconnected ? The fluke, which can go display down to one mV, does not do this ! It displays 0.000 Volts when not connected !
So, the mV is clearly way too sensitive. I should note that I desoldered the large RF shield at the back of the main board, in order to get access to the components et see where the traces where going etc... could this have such a huge impact ?
If this is not it, then I guess there must be some voltage inside the meter that's somehow "leaking" into the mV range input path ?
Inspection of the meter and trouble-shooting :
I disassembled and re-assembled the meter several time.. and eventually one of the pins of the LCD header broke off... but I was able to temporarily fix it by soldering a thin/wire wrap wire between the two boards. Works just fine. I will order a replacement header shortly. Found a gold plater on Farnell' site, so even better than the original.
I checked the PTC, reads just fine a 1100 ohms, which is spot on it's rated value, according to the data sheet I found for it online.
The 4 MOVs look fine as weel : like new on the outside, and all 4 are very high impedance. don't know how much because the Fluke couldn't even measure it, so I guess that means at least 20Mohms, which I guess is good enough. The readings on the Vdc range where all fine, so I guess it must be OK ?
I found that the LM385 1.25V voltage reference (small TO92 package) was bent in order to be able to close the meter enclosure, and that as a result, pins 2 and 3 looks like they were touching ! So I re-arranged them a bit, but that didn't change anything to my test results.
I also found a group of 4 few dipoles on the back of the board, in the fuse area. I don't know what kind of device it is... but they work in pairs : one pair is connected to one of the fuses, the other two, to the other fuse.. Not knowing the nature of the component, I ventured testing them with the ohm meter. They read in the order of the Mega ohm (both ways). Ranging from 0.7M up to 3M. I guess they this high impedanc is normal, because I also found teh exact same component, lonely this time, on the top side of the board. It is stuffed between 2 jacks, and is electrically connected straight across the 9V battery terminals ! So indeed it batter by high impedance... now what are there purpose and technical nature.. no idea. They just dont look like resistors, and although they have color coded rings, they carry only 2 color rings, a bit too few to be a resistor...
Two of them looked like they had not so good solder joints, so I reflowed them all... but didn't change or improve a thing. Oh well, at least it couldn't hurt I guess !
I also found a little bit of corrosion on the PCB, at the base of the negative battery terminal, due to the old battery leaking I guess. So I desoldered the terminal so I could give it a good clean, then soldered it back. Again, this didn't change a thing to my problems...
Lastly, when examining the main PCB to see how it compared to the pics posted by Robomeds, I noticed that it's all similar except that the 4 MOVs are laid out in a row instead of a 2x2 square, and that the PTC and the yellow 200ohms resistor (R1 and R2 then), were relocated further down, in between the Volts and COM jacks. Not that it matters of course. Anyway, nex tto the MOVs, I notice R25, a 10M 1% resistor. I supposed it's purpose was to achieve the typical 10Mohm input impedance that's pretty much standard for digital meters. So I could not help but measure it, in circuit first. At first, as soon as I applied the probes to its leads, it would read 10M... great, how unexpected... but a few seconds later, the value started DROPPING ! Slowly but surely, after a couple minutes measuring the thing, it would eventually settle at around 8,5M, so much for the 1 % tolerance ! What an odd behavior for simple resistor, I thought. Maybe some capacitive effect in the surrounding circuitry then. So, I lifted one of the resistors terminals, so I could get a valid measurement. guess what ? It behaved exactly the same ! So this resistor is clearly acting very funny ! Actually I am not so fussed about the actual value of it, as I don't think it would influence the slightest bit the validity of the measurements, after all its only purpose is to provide a high impedance... but that's not required in my test procedures, since I feed the meter with low impedance source voltages, my lab power supply ! No, what really worries, puzzles etn troubles me, is the fact that is unstable ! This means there is something definitely wrong in this resistor, and since it is by essence, right in the signal path, god knows what effects that might cause... Sadly I didn't have any 10M or very high value resistor in stock to replace it with for test purposes.
So... where ma I now ?
My best guess :
- for the 10A range reading too high, try and do what it takes to recalibrate the thing and take it from there.
- For the mV range being overly sensitive when the probes are disconnected, two things : 1) the faulty 10M input resistor my be partially "open", on its way out, which means the meter is kinda measuring straight from the DMM5 chip input, which must be extremely high of course, explaining why it is so sensitive. That, and/or the absence of the RF shield.
- About the capacitance range bug, it may as well be related to the above problem, we shall see.
So, to conclude : I will get a brand new 10M 1% resistor, then solder the shield back on, then replace the LCD header on the main board, then build a cable a recalibrate the 10A range. Ah, and contact Chauvin-Arnoux/ Metrix to see if they would be kind enough to send me a service manual for this meter, or at least the schematics, given that the meter is 20 year old and not marketed any more... so hoping they are not going to make too big a deal about sharing data on this particular product !
Will report back as I progress...
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Some more.
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I have a Fluke 12 with the same specifications of 0.9% VDC basic accuracy, but in reality it is within 1 mV of other meters. I bought the Fluke 12 from the original owner and it is pretty much in mint condition.
On Robomed's 5360, I can tell you that when I measure the input impedance of the mV (with 5360 set to mV and unit powered on), it reads a solid 9.95 Mohm on my Fluke 87V.
If R25 is the 10M ohm resistor that is one that is used for the mV protection, then it sounds like you have likely found the problem. -
Thanks, so I am not a fool then, these Fluke 11/12 are indeed way more accurate than they advertise... yet they sell for very cheap used, so maybe I will get another one :-)
Since ti seems you have a Metrix at hand, may I ask you to check what you get on the mV range, to compare with the results I laid down above ?
That is, by how much does it floats when the leads are plugged in to the jacks, but the probes are in free air, connected to nothing ?
For the default/dc range, I errs anywhere from 1mV up to sometimes 80mV. But the fluke 11 does not float at all, it's a steady 1 or 2 mV maximum.
Then what do you get if you press the yellow button to switch the mV range to the "AC + DC" mode ? In this mode, it floats at ridiculous/crazy high values, almost fulls scale : hundreds of mV ! 150, 300, 450 (full scale being 500mV...) ! What do you get ?
Yeah I think R25 is the one.. I mean I don't know what other purpose a 1% 10M resistor could have, if not to set the input impedance of the meter... but I will go to the bench to examine the PCB traces more closely to confirm this likely theory... just to be 100% sure.
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The 500mV range on the MX 5x meters is high impedance, like on a 'real' lab grade DMM.
No wonder it shows overload if connected to nothing, as the input current of the frontend will eventually charge the input capacitance to a out of range condition.
And of course, the shields are essential in this "electrometer" mode.
I would be careful with the current range as well. Don't attempt to touch the calibration unless you have the means to _really_ confirm that the readings are way off. (And if they actually are, I'm quite sure something else would be horribly wrong and it's nothing to be cured just by re-calibrating the thing)
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The 500mV range on the MX 5x meters is high impedance, like on a 'real' lab grade DMM. No wonder it shows overload if connected to nothing, as the input current of the frontend will eventually charge the input capacitance to a out of range condition.
Good evening Performa,
Well... you are right.. and wrong. The MX5X is not a real high-impedance meter on the mV range. But.. it CAN be.... it asked to !
By default, the mV range uses the standard 10M impedance like all the other ranges. If you WANT the high-impedance (stated in the manual as greater than one Gohms), then you have to explicitly ask for it, by pressing the "range" button on the little keypad at the top of the meter, while at the same time, turning the main knob to power the unit on. The LCD will then briefly inform you what the impedance is, 1G or 10M., tried it, worked just fine. The meter will the remember the setting and store it in the external cal EEPROM.
But the over-sensitivity I am experiencing in the mV range is observed when the standard 10M impedance is selected (I measured it to be sure)! Rest assured... I also turned on the High-impedance mode to see it made any difference... it doesn't, not the slightest change.
Still, this in itself is a clue, as I mentioned in my previous mail: this comforts me in suspecting that the 10M resistor is indeed faulty (replacement on its way), which then would mean that basically the meter is in high(ish)-impedance all the time, no matter what impedance I set it to !QuoteAnd of course, the shields are essential in this "electrometer" mode.
OK thanks, wasn't sure just how critical it was in this situation. Will solder it back , as soon as I have replaced the 10M resistor (don't want to solder it back and off again 2 days later !...)QuoteI would be careful with the current range as well. Don't attempt to touch the calibration unless you have the means to _really_ confirm that the readings are way off.
"really off" ? Hell, a blatant, undisputable 40% off... I do'"nt need a 7 digits 1000 buck meter to tell me it's way off ! Such a meter would be nice to know if the Metrix is off by 39,567876544 % insteand of just "roughly 40%".... but that would not change the diagnostic would it ;-)Quote(And if they actually are, I'm quite sure something else would be horribly wrong and it's nothing to be cured just by re-calibrating the thing)
Ah, I never said it WAS the calibration, did I ? Don't think so. I only said it was a reasonable/plausible cause, given the age of the meter which is way past the guaranteed retention period of the calibration EEPROM. And old gear losing their car is just common place, the web is flooded with people have to deal with such issues, and not just devices with volatile/battery-backed NVRAM....
So it's just an hypothesis, at this point... nothing more...
One argument to go your way, would be to say : "how comes the cal on the 10A range is so off, while all other ranges read just fine ?". Indeed it seems rather unlikely that the cal EEPROM would lose the bytes related to the 10A range, and preserve all other bytes ! ;-)
Still, I find it nice and interesting to build the serial cable and get the cal software, if just to be able to "talk" to my meter, even if it's just to say "hi", and not touch any cal data ;-)
So... what could explain this huge error on the 10 A range ? Don't know.
What we can see so far is taht the DMM chip can read voltage just fine, even very low signals on the mV range. So technically it should be able to measure the voltage drop just fine across the current shunt. So what's next in the current measurement "chain" ? The shunt of course... maybe it is 40% off, which would then translate in a 40% error when the DMM chip reads the voltage across its terminals. BUT... as I noted yesterday, the uA reads just fine ! So clearly the shunt is good. So.. what's left ? The shunt is good, and we know the DMM chip reads voltages just fine. So, one can only assume that there is some external/analog circuitry between the DMM chip and the shunt, which is specific/ only used by the 10A range, which would introduce this 40% error. I am plenty willing to admit this, and this is precisely why I am trying to get hold of the schematic, so I can see exactly how the circuitry is put together, so I can see where the error may be coming from, knowing it's not the chip nor the shunt.
I e-mailed Chauvin-Arnoux/Metrix this evening, asking for whatever technical documentation they may have and be willing to send me. They happen to have an office just 40 miles from me, so I offered to pay them a visit if need be, to discuss the issue. -
I've had a chance to check out a couple of your issues on the 5390 unit I have here.
1) Regarding the mV alarm: It definitely alarms at anything over 500mV (or below -500mV).
In 10M impedance mode, it does not alarm arbitrarily with leads in or out, because even though it wanders a bit as expected (tens of mV), it does not exceed 500mV. No amount of fiddling with the leads would get it over 500mV.
In high-impedance mode, it doesn't alarm if you leave it alone with no leads connected. But with leads connected, it wanders quite a bit, especially if you handle or touch the leads, and every time it goes over 500mV it beeps. If you connect stimulus over 500mV and then remove it, it takes quite a while for the charge to dissipate, with the alarm going the whole time. Engaging AC+DC mode does increase the sensitivity somewhat.
I'm not sure why this alarm is necessary, but if its purpose is just to go off when the input is over 500mV, I'd say this unit is working as designed. With input impedance over 1G, it's easy to pick up a charge on the leads.
2) Capacitance range: Displays 00.00 with an occasional 00.01. While measuring displays "run" in the top half of the display. Upon disconnecting the cap, it will display "run" again very briefly then return to 00.00. If I short the leads it says "run" for 30 seconds, then displays "0.L". -
Thanks Robomeds for this post !
I am French and boy I struggled to tear my MX 55 apart... it took a chap from the other end of the world to tell me how to open "our" meters ! LOL So thank you for detailing the procedure to put it to bits. Armed with this, I will make a new attempt at open it !
I agree with everything you said : great meter overall, I just love it and always wanted one when they were new 20/25 years ago and I was just a kid dreaming as I saw them tested in the electronic magazines of that day ! They were worth about a month of salary IIRC.
As for the history part, I read some thins wrong above, so I would like to correct.
It's easy to get lost because Metrix's life has been such a roller coaster throughout the years ! One day merging with similar companies to form a group, another day getting bought by a group or part of a group, then sold again to XYZ ! Hard to follow.
But to put things simply :
Chauvin-Arnoux and Metrix are both very old big French names in the instruments business, alwyas have pionnered the market, alwyas designed their stuff in house of course, and still do taody ! Their R&D centers are still in France.
Chauvin-Arnoux was formed as far back as 1893, and Metrix in 1936, first famous for they vacuum tube test gear, as it was the technology of that era.
The two were then competitors, Chauvin-Arnoux always wanting to buy Metrix... which they eventually did later.
As for the ITT thing :
In 1964, Metrix got "affiliated" to ITT, nothing more.
In 1970, Metrix merged with a few subsidiaries owned by ITT, to form a group.
In 1979, the Metric products were rebranded " ITT Metrix "
In 1990, Metrix was the leading manufacturer in the whole of Europe, for analogue and digital multimeters.
In 1994, and of the ITT affiliation : Metrix got sold to a group of companies (mostly French and German).
... which had overambitious plans for Metrix, 3 years later, the group, and Metrix with it, bankrupted.
... that leads us then to 1997. This were Chauvin-Arnoux offered to buy Metrix, the judge in charge accepted... at long last chauvin(arnoux managed to buy his competitor Metrix !
The two French big names are now united in the same group. Chauvin-Arnoux was/is clever enough to let Metrix design and build their own stuff, sold under their own Metrix brand, so nothing has changed. Metrix is still Metrix... except it's now out of trouble financially because Chauvin-Arnoux owns them.
So basically, it wall started a century ago with Chauvin-Arnoud, and a century later, after troubled times, it all ends with the same two brothers ! Except they are now joining forces, instead of competing against one another.
Here is a link to a PDF emanating from Metric, that describes the whole story, written in French obviously sorry, but I highlighted the main points above.
http://www.geode-annecylevieux.org/____assets/uploads/2012/01/METRIX.pdf
As for the chip driving the MX 50 series, I don't know its story. Obviously Metrix were not big enough to have their own manufacturing plant, so maybe they designed the chip in -house and just asked ITT to manufacture it for them... or did ITT already have this chip in their catalog and let Metrix use it to roll their MX50's around it.. or was it a joined effort / co-development, shared between ITT and Metrix... who knows really, not that it matters in the end... the result is a great meter ! :-D
As for BK et AEMC of who ever else, it was obiously just a rebadged Metrix.
Anyway, sorry for the length... I came here as well to ask Robomed or anybody else... if there is a schematics or service manual available somewhere for the MX 50s series ?
.. because my MX 55, which is externally/cosmetically in like new.. must have something wrong deep down, as it acts weird and funny and pretty much every function but the current measurements. I suspect most of the weirdness might be a problem with the input protection circuitry, but there is one misbehavior which I fear might not be as easy to diagnose : in the mV range, it screams at constantly. The "high-voltage"/danger alarm and icons, come on as soon as I set the switch/knob to the mV range, even though the test lead are not connected to anything. shorting the leads makes the alarm go off.
Anyway... would be great if I could have a schematic for this baby, to help me trouble-shoot the thing... because I just love this meter and although it is extremely sick at the moment, I will not give up on it without a good fight !
No idea what kind of abuse the meter might have experienced to show so many problems... it was already like this when I bought it used, 3 years ago... the seller never mentioned anything about any kind of problem.... that's honesty for you ! :-/
Oh, before I go, for those interested, I attached a couple PDF files below. Commercial leaflets of the day, presenting the MX 53/4/5/6 series (in English) and another leaflet (in French) presenting the later/revised ' C ' version of this range of meters.
Merci beaucoup! Thanks for straightening out the history. Really helpful. -
So... what could explain this huge error on the 10 A range ? Don't know.
What we can see so far is taht the DMM chip can read voltage just fine, even very low signals on the mV range. So technically it should be able to measure the voltage drop just fine across the current shunt. So what's next in the current measurement "chain" ? The shunt of course... maybe it is 40% off, which would then translate in a 40% error when the DMM chip reads the voltage across its terminals. BUT... as I noted yesterday, the uA reads just fine ! So clearly the shunt is good. So.. what's left ?
Be aware that each current range has its own shunt resistor.
So it looks like the 10A shunt is bad, even though I cannot imagine how this could happen. A severe overload maybe, but then the fuse F2 should have blown and protected the shunt.
You could check the resistor, whether it looks discolored or otherwise damaged, also check the solder joints - even though bad solder joints could not explain too high a reading as the shunt has to have a 4-wire connection anyway.
The 10A shunt has to be <50 milliohms.
I would check its value. If it looks too high, then I'd calculate a resistance value that can be connected in parallel in order to bring the total resistance down by 40% and finally use a piece of thick Manganin resistor wire to build a shunt for the shunt
After that, the 10A range should be close enough so it can be calibrated. Because I doubt that a 40% error could be corrected by calibration. Even if the permitted adjustment range is wide enough (after all it's just a firmware decision), the input voltage might get too high and the meter would then be unable to actually measure 10 amps.
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I can't imagine that shunt getting thrown out of value. I suspect something else is the issue. I would start by visiting Modemhead's blog. He talks about repairing several damaged meters. In the discussions he talks about the various innocuous seeming things that can throw your readings to the birds. I would also watch Dave's videos on protection circuits. When those go bad they don't always disable the meter. Sometimes they just result in odd readings.
PS: My 5390 had the out of range warning all the time in the mA range. It was actually kind of annoying when you just put the leads down for a moment and the meter starts beeping at you. Still, good meter though I admit, mine has been pasted to more deserving hands.