Metrix MX56C / BK Precision 5390 Multimeter Teardown - Page 1
Forum section: electronics / testgear

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 20, 2013, 03:58:42 am
content: Recently I picked up a BK Precision 5390 to complement my 5360. Thanks to one of Dave’s videos I discovered that the 53_0 BK meters were Metrix MX series models made in France no less. The 5360 is the MX53C and the 5390 is the MX56C. The less one is a 50,000 count, .1%+2counts meter while the 5390 steps up to 50,000 count at .025% +2 counts. Quite impressive specs.The meters are also IP677 rated thus meting the same 1m submersion standard the Fluke 27 claims. I doubt they are as rugged as the 27 but if you like to swim with your meter, well these claim they can go.I’m going to skip over much of the usage discussion. Overall I’ve found these to be nice to use meters. The continuity tester is quick but scratchy. The auto range is plenty quick. They have a touch hold function similar to a Fluke as well as conventional hold features.For me, the build and design is what makes this meter more interesting. Forgive me but I think it’s a bit like the few older French cars I’ve been exposed to. Sometimes you wonder why they did something so much different than the rest. Other times you wish the rest would copy this feature or that.Prior to opening this meter I have a few comments. The case feels very solid. No flex at all. The tilting stand is small and cheap feeling. It doesn’t lift the meter up that much. The interesting thing is the stand is meant to be detached and used as a tool to open the front mounted battery door. As part of the ASYC II safety stuff the battery door is actually the front panel of the meter. Thus you must disconnect the leads in order to access the battery. The battery cover snaps in place on the sides and the stand is used to unsnap the case.Before we go deeper, the control knob is easy to grasp but feels a bit metallic and certainly sounds metallic. The 5390 didn’t come with original leads but my 5360 came with leads that would seem reasonable for a $50 meter. I don’t think these were in that price range when new.So pulling the front panel off we see a water proof secondary cover over the batteries and fuses. The walls of the battery/fuse compartment act as blast walls for the fuses. The fuses themselves are ceramic, 600V units rated to 1.5kA and 30kA interrupt current (.63A and 10A). Needless to say they don’t look impressive next to those in a Fluke 87. It’s interesting as this meter looks like the safety features aren’t as impressive as the Fluke 87 but things like the IP rating suggest this was meant to be a rugged meter, not just a battery operated bench meter.Anyway, let’s start opening things up.The button panel is unsnapped from the side. The membrane of buttons lifts out of the front of the meter. The bottom removal is VERY interesting. You press in on two tabs molded into the upper housing. That allows you to unsnap the lower housing. There is a large, white gasket between the two as well as some decent wall overlap.Once inside we see the back of the main PCB. Note the gold colored plating where the terminals are bolted to the PCB. Very clean construction. The RF shield is soldered in place and includes a foil patch over some adjustment caps. To remove this PCB we again deal with snaps! The bottom of the board is held in by the nuts but the top is held in place by a snap feature integrated into the screen surround which snaps into the upper housing. Once you know about these snaps the meter is rather easy to open.This is a good place to cut this off and continue in a new post.

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 20, 2013, 04:14:46 am
content: The rest of the disassembly is a few snaps and disconnecting the header between the display and main boards. The construction quality seems first class to my semi-trained eye. Note the black foam gasket under the area where the battery would sit. I assume this is meant to further prevent dirt from migrating in the meter.Looking at the safety bits, I see no cut outs in the board. I assume they maintain decent spacing. The blast shielding for the fuses is integrated in the battery compartment. It’s worth noting that the meter will not operate if the high current fuse is blown. It will just say Fuse 2 on the screen. If Fuse 1 is blown it will say Fuse 1 when in the uA/mA range. There is no input jack warning.On the high voltage side we have a PTC and 4 MOVs. I believe I saw a family of diodes under the RF shielding on the back of the board. Overall it looks better than the other meters I’ve been showing recently.The current shunt is also not like any other I've seen. No idea why they used a sheet metal 'M' rather than the normal wire. Perhaps they just wanted to have M for Metrix in the meter.Other features worth noting are the adjuster caps including C14 and the resistor hybrid next to it. The selector knob consists of a blue frame and the white rotor with contacts that wipe the board. The blue frame has pins which limit travel. One of the two ITT-Metrix chips can be seen.Note the IR couple in the black gasket area. I don't quite know how Metrix expect that to be used given that you must remove the battery cover to access the IR interface.

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 20, 2013, 04:21:22 am
content: Moving further up we see the main Metrix DMM5 chip. Ah, the famous DMM5 which I had never heard of earlier this evening.There is an interesting Analog Devices regulator near the main chip, an AD636JH 9625.Edited to experiment with pictures.

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 20, 2013, 04:27:54 am
content: Next we have the screen and button interface board. The buttons are membrane type. I checked on the 5360 and like many meters it has unused "buttons" under the panel. The 5390 has a full complement. Anyway, a few of the contacts are interesting in that 3 rather than 2 pads exist under the buttons. There is basically nothing but the button pads and traces on the screen side of the board. The so-so green LEDs are also on that side. The back size uses an NEC asyc to run the screen.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 20, 2013, 05:19:25 am
content: Well,I Love These Meters ,Very Solid And If There is a Fight In The Lab you Know what i Am Talking About ;-)

author: Wytnucls
author_rank: Super Contributor
timestamp: July 20, 2013, 06:23:42 am
content: Interesting meter.Some corrections:There is no MOV, R2 is a Gas Discharge Tube (Spark Gap) fulfilling the same function.AD636 is not a regulator but the True RMS to DC converter (1% max error version).The IR diodes are probably only used for software calibration.

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 20, 2013, 12:49:27 pm
content: R2 is a PTC, the print was hard to read but it said so on the side. The MOVs are RV1-4.If the IR diodes are only used for calibration I don't understand the RS232 output of this meter. When you press the print button the meter outputs vs RS232. Those LEDs are the only such interface I noticed. Thanks for the info on the TRMS converter. The 5360 didn't have that particular part. Then again its accuracy wasn't as high either.

author: Wytnucls
author_rank: Super Contributor
timestamp: July 20, 2013, 04:43:23 pm
content: Here is the manual:http://www.chauvin-arnoux.us/pdfs_aemc/user-manuals/MX56_EN.pdfIt does have a RS232 print function, with the optional adapter:http://www.testitnow.co.uk/media/files/test_equipment_manuals/Metrix-Chauvin%20Arnoux/Metrix%20MX56.pdf

author: zaoka
author_rank: Frequent Contributor
timestamp: July 21, 2013, 04:08:18 am
content: It has been sold under AEMC name as well. Did not know they are made in France.I remember long time ago AEMC offered there meters at huge discount. I have seen them under ITT name as well.

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 21, 2013, 04:22:06 am
content: Who is ITT? Clearly they are more than an Extech since their name is on the main IC.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 21, 2013, 06:16:29 am
content: Robomeds ,I Have a suggestion When You Make a Review Like This .I Can Let You Know If you Have No Issues .

author: free_electron
author_rank: Super Contributor
timestamp: July 21, 2013, 06:20:31 am
content: Jep. These are originally ITT machines. Itt intermetall doesnt exist anymore. They were a large ic maker from germany. The ITT concern made tv's , vcrs and other stuff. They were large in automotive as well. Many upscale german cars from the 80's and 90's had itt chips in em.Itt invented the digital television. Digit2000 system. The digitized the viadeo and audio in the tuner and the rest was a collection of 40 pin dip ic's on a bus. There was a pal decoder, secsm decoder, teletext chip, nicam chip, main cpu, deflection processor, rgb processor and many more.Depending on what features you wanted tou just plonked chips on the bus. The software did the rest.The silicon division was acquired by Nokia in the mid 90's and later merged with the Micronas group. The digit 2000 platform lived on for a while in some micronas chips. Up till a few years ago there was a combo chip that basically had the whole audio/video digital processor in 1 chip. These were used frequently in pc tv tuner cards. When analog tv disappeared micronas folded that business. Micronas still makes specialised automotive chips for sensors. They even have special cpu's(based on 6502 architecture!). They still use the silicon plant in Freiburg Germany that was the ITT intermetall plant.ITT had a test and measurement division as well. This meter is one of them. They are very good designs. At the time of their relase Fluke was unknown i europe and these were the rolls-royce of the meters. chauvin-arnoux was a large french distributor of test euwipment and components and they rebadged them.All those components you see in there (melf resistors, caps, trimpots) are made by ITT. they did everything. Even the lcd glass.ITT knitter still makes switches today. So does ITT cannon.The rest is gone, spun off.At their heyday they rivaled Philips in terms of making every single component from wire to resistor to led to chip in house.ITT still exists and does many things but no longer semiconductors and consumer goods.ITT is short for internstional telephone and telegraph company. They are a very old company. Pre world war 1 i believe.Actually the ITT university and career decelopment centers are owned by them.They still have a large protfolio of components.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 21, 2013, 06:28:30 am
content: Quote from: free_electron on July 21, 2013, 06:20:31 amBoss ,Beautiful Info .I still did not get one thing ? .Someone was making for chauvin or they were making it using stuff from itt ? .As far as i know BK precision ,AEMC And Metrix have these type of multimeters .BTW i still see some little different once on chauvin website .They made some awesome jaw dropping Analogue multimeters also

author: free_electron
author_rank: Super Contributor
timestamp: July 21, 2013, 06:35:41 am
content: I just looked up itt on wikipedia. You need to read that. Those guys are huge , but virtually unknown to the masses.They even bought farnsworths tv business! They invented digital phone exchanges, pulse code modulation, fiber optics and all kinds of other stuff.http://en.wikipedia.org/wiki/ITT_CorporationI knew the intermetall group well as i was a trainee in 1989 and the two successive years at Nokia in Finland (when i was in highschool i won a contest sponsored by Rotary. last-year students(18 years) from many schools had to make a practical project. I had made a satellite receiver based on a tuner from nokia salcomp(the metal can) , a 8051 ah basic and a rgb decoder TDA4550 i believe.. It could point the antenna and had an infrared remote control. I won first prize, which was 2 months as an intern during summer holidays in a company of you choice. I picked Nokia in finland. I spent three summers there. I was in Kemijarvi , just above the polar circle. 24 hour daylight). As an 18 year old i was tinkering with 40Ghz spectrum analyzers... Building digital satellite receivers (D2MAC )...When they just began designing with the digit2000 chips. A few years later Nokia acquired that group and fused it with their micronas group. They are today still in freiburg, germany where intermetall began.

author: free_electron
author_rank: Super Contributor
timestamp: July 21, 2013, 06:39:04 am
content: Chauvin rebadged the itt meters. Chauvin doesnt make anything. They buy in bulk , specify color and slap their name on it.ITT metrix was rhe test and measurment division of ITT. That group was in france. The chips came from ITT intermetall in Freiburg, Germany. All other components you see came from various ITT divisions all over the world. My estimate is that 95% of the parts in that meter were made by ITT divisions. Those guys did everything.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 21, 2013, 06:42:37 am
content: Quote from: free_electron on July 21, 2013, 06:35:41 amHeavens Goodness ,I Searched For ITT Multimeters and Here You Go .Bloody Hell Never New This .BTW You Know i Am In such a Country Where Doing Business And Importing Is a Big Big Issue .Very Often i Do Buy Old ITT Akka Chauvin Akka Metrix Aka BK Precision Multimeters And They are still spot on " Checked " With Voltage Standard DMM Check Plus .The Last One i Had I Sold That .These Things Are Heavy And Built Like Tanks .Thats Why i Was Saying On The Lighter Side That If You Do Indeed Have a Fight In The Lab You Know What Instrument You Can Use there Lol .

author: free_electron
author_rank: Super Contributor
timestamp: July 21, 2013, 06:52:56 am
content: Correction . I said itt knitter , but it is ITT Schadow that made switches together with ITT cannon.They are now c&k and alps.Knitter is a different company that still exists and ITT cannon still makes many connectors.A well known switch was the Digitast. A spring loaded pushbutton that had a unique property : it does not have contact bounce.You need to read the history of ITT. They basicaly were the grandfather of Alcatel , the system 12 phone exchange, that today is srill in production by alcatel. BTM is Bell Telephone Manufacturing in antwerp Belgium...They owned Avis , the hartford group , hotle chains.They did dirty work topplling and installing dictators, traded in arms, got sued by the government.Sheesh what a company ...

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 21, 2013, 01:19:37 pm
content: Quote from: Amarbir[Lynx-India] on July 21, 2013, 06:16:29 amSure, my feelings aren't to fragile

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 21, 2013, 01:25:10 pm
content: Mods ,Please Delete This Post

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 21, 2013, 01:25:57 pm
content: QuoteThanks ,Many Contributors On Forums Feel Not Quite Easy When Someone Does That ,Thanks Here You Go ."I Feel That When i Followed Your Article ,I Had To Use More then brain power to go with the flow .This is what i do when i do something like this i mean the review .I attach the pictures to the thread and then i get the location of the images and i embed then one by one under the text of the stuff i write .Something like this ->http://www.lynxchandigarh.com/scripts/betaforums/showthread.php?t=2326.You Will See I Have The Pictures Attached ,Thats All i loved the article though

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 21, 2013, 01:59:00 pm
content: Amarbir,I understand what you mean about trying to get the pictures and text inline. Is there a way to do that using this forum to host the images? In your link I only see the image links at the bottom of the post. I did see that you changed the image names.Thanks,

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 21, 2013, 02:06:30 pm
content: Quote from: Robomeds on July 21, 2013, 01:59:00 pmNo ,I Can See The Files In Post Also "Might Be You Need To Register " ,But My Intention Is not To Force You To Register And See File ,But To Explain You How Its Done .You Just Try That And Hopefully you will Have a Crystal Clear Idea .I Am 100% Positive It Can Be Implemented And It Will Work Here .Let Me Try The Same In This Post OnlyAll The Stuff You Wanna Put Across To Us In The Forums Goes Here

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 21, 2013, 02:09:16 pm
content: Sir ,Check This Post Up Now .You Will See I Attached The File First Then i Saved The Post Then i Edited In Another Tab And Took Direct Links Of The Pictures i Attached From Older Tab And Embedded Them In The Post .

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 21, 2013, 02:35:28 pm
content: OK, I see what you did and was able to get it to work in preview. Now I have a style question. If I put the pictures in line will they shrink in size? In the preview the picture was full size in the text. That might be a problem for people with a slower connection or smaller screen. Alternatively I can put a thumbnail in line so you can see which image I'm talking about but if you want to see it in detail you have to click the link at the bottom of the post.Thoughts?

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 21, 2013, 02:44:42 pm
content: Quote from: Robomeds on July 21, 2013, 02:35:28 pmRobomeds ,Please Do The Same For One Image And Let Me See How That Goes .I can only advise you after i see that .

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 21, 2013, 03:04:36 pm
content: Amarbir,Take a look at the third post in the thread.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 21, 2013, 03:37:29 pm
content: Quote from: Robomeds on July 21, 2013, 03:04:36 pmWell,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.

author: retiredcaps
author_rank: Super Contributor
timestamp: July 26, 2013, 07:30:55 am
content: 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.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 26, 2013, 12:37:30 pm
content: Quote from: retiredcaps on July 26, 2013, 07:30:55 amWell ,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

author: macboy
author_rank: Super Contributor
timestamp: July 29, 2013, 12:05:26 am
content: 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.pdfbut it does not include the special calibration commands.The calibration software (AK5350) is discontinued and is now freely downloadable from the B&K website atwww.bkprecision.com/downloads/software/AK5350.zipbut 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.

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 29, 2013, 12:52:19 am
content: 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: September 27, 2013, 05:05:37 am
content: Quote from: macboy on July 29, 2013, 12:05:26 amGot a picture of your homemade cable? I'm interesting in possibly building one.

author: macboy
author_rank: Super Contributor
timestamp: September 28, 2013, 12:32:08 pm
content: 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.

author: TheEPROM9
author_rank: Frequent Contributor
timestamp: January 30, 2015, 01:59:11 pm
content: 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 30, 2015, 11:39:22 pm
content: Quote from: TheEPROM9 on January 30, 2015, 01:59:11 pmGood score for free.

author: Vince
author_rank: Super Contributor
timestamp: August 26, 2016, 11:35:01 pm
content: 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.pdfAs 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 ! :-DAs 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 27, 2016, 12:43:14 am
content: Quote from: Vince on August 26, 2016, 11:35:01 pmSome 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?QuoteAnother member, modemhead, now has Robomed's BK 5390. He can verify the above.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 27, 2016, 12:50:10 am
content: 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.

author: ModemHead
author_rank: Frequent Contributor
timestamp: August 27, 2016, 02:31:51 am
content: 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.

author: Robomeds
author_rank: Frequent Contributor
timestamp: August 27, 2016, 04:15:08 am
content: 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.

author: Vince
author_rank: Super Contributor
timestamp: August 28, 2016, 08:03:41 pm
content: 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- CapacitanceSo, 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...

author: Vince
author_rank: Super Contributor
timestamp: August 28, 2016, 08:23:07 pm
content: Some more.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 29, 2016, 02:15:03 am
content: 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.

author: Vince
author_rank: Super Contributor
timestamp: August 29, 2016, 03:35:08 pm
content: 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.

author: Performa01
author_rank: Super Contributor
timestamp: August 29, 2016, 04:43:29 pm
content: 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)

author: Vince
author_rank: Super Contributor
timestamp: August 29, 2016, 06:22:05 pm
content: Quote from: Performa01 on August 29, 2016, 04:43:29 pmGood 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 !QuoteOK 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 !...)Quote"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 ;-)QuoteAh, 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.

author: ModemHead
author_rank: Frequent Contributor
timestamp: August 30, 2016, 12:44:05 am
content: 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".

author: redg
author_rank: Regular Contributor
timestamp: August 30, 2016, 02:39:05 am
content: Quote from: Vince on August 26, 2016, 11:35:01 pmMerci beaucoup! Thanks for straightening out the history. Really helpful.

author: Performa01
author_rank: Super Contributor
timestamp: August 30, 2016, 09:22:11 am
content: Quote from: Vince on August 29, 2016, 06:22:05 pmBe 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 shuntAfter 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.

author: Robomeds
author_rank: Frequent Contributor
timestamp: August 31, 2016, 03:06:43 am
content: 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.

author: Vince
author_rank: Super Contributor
timestamp: August 31, 2016, 01:53:28 pm
content: @ModemHead : thanks for taking the time to carry out those tests, much appreciated !@Performa : TWO current shunts, a separate one for the uA range ? Hmmm if you say so, OK why not ! Will investigate for sure... that's a good lead.OK gentlemen... now hold on to your chair, fasten your seatbelt..... you just won't believe it... I certainly can't but... it's true !Remember I said I would contact (via e-mail in this case) Metrix / Chauvin-Arnoux ? Well, I did.... and guess what, who would believe it.. today they actually REPLIED to me !This in itself kinda stunned me, I mean who would bother replying to something like this....So, OK they replied to me, but I fully expected something like "sorry we can't help you, have a good day"...... but no.... NO !This is what they wrote : "Dear Sir. Please find attached the documentation that we are able to supply. Wishing you good reception, best regards".WHAT ? They actually sent me something ?! Let's see what do I have in terms of attachments.... WHAT ?! WHAAAAAAT ?!OH !!!!They did it !! They sent me the FULL SCHEMATICS for the thing ! 7 pages of schematics !!!!!!And two pages showing the two sides of the board with components overlay. Material clearly destined to in-house use : targeted at the workers who actually assembled the PCB/soldered the components (everything but the SMD I guess) ! With annotations to tell them "here, watch out for this hole in the PCB, make sure you don't obstruct it", or "capacitor X and Y, bend them to lie on the PCB" and " C24 must be soldered right on the terminals of Chrystal Q4", etc !The drawings also shows the main board and the LCD board as a single board, they were not yet separated at this point.Oh boy this is all priceless, it's golden !And all this kinda hand drawn it seems.I only had a quick look at it, but let me tell you , it's electronic porn ! I feel so privileged to have these schematics, it's like a time machine and a door inside their facility, production line and R&D lab. Such a joy to see all these schematics ! I really feel so lucky, like a kid left alone in the middle of a sweet factory ! LOLIt's so cool !I so wish I could share them with you here ! SO frustrating to have to keep them just for me ! Well.... the person who e-mailed me didn't say anything about me being allowed or not to share them, but the footer of her e-mail carried the usual "every information or document is solely destined to you and no reproduction is allowed without explicit consent of Metrix " blah blah blah.... but this is most likely the usual footer that mail servers in pretty much every company these days, automatically append to any out-going e-mail ! So... not sure what to do !Anyway, I am SO HAPPY !I will take them to work so that I can use the big copier there, to print all the schematic pages in large A3 format, which is their original format. That will make it easier and more comfortable to read.What a good day !Oh, forgot. they actually sent me the schematics for the later 'C' revision of the MX55, not my old/vanilla 55, but the differences are so minor, it doesn't really matter. The main difference in the 55 C I believe, is a few more special functions using more buttons at the top of the meter (like print, duty-cycle IIRC, things like that), but all that stuff is likely implemented in software, so the actual hardware on the board is unlikely to be fundamentally different, if at all.The schematics are dated year 2000. The annotated board layout destined to the production line, is a bit more recent, dated 2005.. well actually the bottom side of the board is. The notes for the top side of the board are still 2000 like the schematics.So I guess that means the last MX 50 series meters were built in 2005 or maybe a little later.

author: Performa01
author_rank: Super Contributor
timestamp: August 31, 2016, 03:52:49 pm
content: Quote from: Vince on August 31, 2016, 01:53:28 pmWell, EACH and EVERY current range has to have its dedicated shunt resistor and my MX54 from the mid-90s has five of them: 500µA, 5mA, 50mA (the one with the increased accuracy, 0.05%), 500mA and 10A.The 10A shunt is a big meander shaped piece of resistive sheet metal.The others might not be so obvious, but you only have to deal with the 10A shunt anyway.

author: Vince
author_rank: Super Contributor
timestamp: August 31, 2016, 07:55:59 pm
content: Yes, now I come to think of it, it make sense as you say. If one wants to conserve a similar resolution for every current range, then you have to come up with an optimized shunt value every time, so as to match the dynamic range of the voltmeter that will measure the drop across the shunt.I will study the schematics to see if I can figure it out... but they are not as simple as I would have thought !....

author: retiredcaps
author_rank: Super Contributor
timestamp: August 31, 2016, 08:25:44 pm
content: On the BK5360, I get using a Fluke 187 with leads relatived out100.84 ohm on 5mA range10.51 ohm on 50mA range1.54 ohm on the 500mA range0.03 ohm on the 10A range

author: retiredcaps
author_rank: Super Contributor
timestamp: August 31, 2016, 08:28:23 pm
content: Just to confirm, you have no other way to verify that your power supply is within its stated calibration in the 10A range? Even a cheap $5 meter with a 10A range?

author: retiredcaps
author_rank: Super Contributor
timestamp: August 31, 2016, 08:32:55 pm
content: In this picture, circled in red, is your range switch. There seems to be a lot of dirt and debris which could cause problems. See modemhead's blog for 2 case studies.http://mrmodemhead.com/blog/fluke-83-iii-rotary-switch/http://mrmodemhead.com/blog/fluke-83-dmm-repair/A generous amount of 91% IPA and letting it dry thoroughly will help prevent problems in the future.

author: Vince
author_rank: Super Contributor
timestamp: September 01, 2016, 02:06:27 pm
content: Quote from: retiredcaps on August 31, 2016, 08:25:44 pmHi there,Thanks for that.I attached below an extract from the schematics Metrix sent to me yesterday. It shows the Amp section. I highlighted in yellow the current shunts.Your measurements are not bad at all, they confirm what teh schematics predict. In the low values you read a bit high, but it gets more and more accurate as the current shunt' value increases.Main 10A one is 0.005 ohmThen it's 1,005 (the mA ranges appear to go through the main shunt, but it's value is so low in comparison, that it doesn't really matter I guess !).Then it's 10.014 then 100.914 ohms.I guess it's obvious that all the shunt values must be close to 10XXX, because it's a 5XXXX count meters, and the ranges are 5XXX full scale of course. So 5/5 =1.... wow, just won Noble prize here ! LOLWe also have another/extra resistor up the ladder, around 900ohms, which would male for a 1k shunt hence a 500uA range... but it looks like this does not go through the fuse, and it's also decoupled by a series capacitor, so no relation to our DC current ranges. Don't know what it's for.... maybe meant for the MX54 Performa mentioned, since it has such a 500uA range. But the presence of this cap in the path of the signal, and it not going through the fuse, has me puzzled.The various taps from this shunt "ladder" then goes to what that multiplexer switch, and the two "AUX1/2" digital inputs are actually coming straight from the main DMM5 chip, so it can select the ranges he is interested in. The voltage drop is read via the "IN2" terminal. We can also see how the fuse blown detection circuitry is put together. The circuitry is not the same for the two fuses.Thanks for the link to ModemHead's blog, looks well put together, will spend some time on it to see the contents. The golden tracks which he describes as "real bad", are actually better looking than those on my meter eh ?! So yes, will make sure to clean that up ! I don't have any of that fancy IPA I keep hearing about on the EEVBLOG. Though it was some gimmick, but the other day I tried cleaning an old board with regular alcohol and boy what a disaster, white traces all over the board, oops.... So looks like this IPA is indeed a necessity ! I will make sure to order some from Farnell. I have not yet sent my order for the LCD header and 1% 10M resistor, as I didn't want to spend 15 Euros of shipping for 4 Euros worth of goods ! Was trying to think of something else I could make use of, to increase the order... well let's add a bottle of IPA to the shopping cart ! :-)About the accuracy of the current indicator/galvanometer on the lab power supply, well I doubt it could be so wrong as to display 2.7 A (max I got) instead of 3.9A (what the Metrix showed). I mean, to start with.. the suply is rated at 2.5A, so no way the manufacturer would sell you a transformer rated/capable of 4A and only charging/advertising you for a 2.5A model ! It would had to be profitable, being so generous ! ... However,, slightly over-specifying the transformer to make sure the customer does get his advertised 2.5A, so he doesn't fell "betrayed", would seem a reasonable practice to me... and that's precisely what I am witnessing on the galva : 2.7 instead of 2.5, so 5 to 10% more. This seems OK to me.However... since it's easy to rule it out, then why not. I do have an modest analog meter, a kit I built when I was a boy... actually from Chauvin-Arnoux ! ;-)It's obviously more of a toy, but still, plenty good enough for we have to do here ! From memory it can only read up to 1A, but still, should be enough to see who is right : the Metrix, or the galvanometer in the power supply. My bet is on the supply, but I want to remain open minded, so will perform the test and report !There is even a simpler test to do ! ! Well... ti's a dual output supply, and both halves are completely independent. so I can just connect the Metrix to second output of the supply, see how it compares ! Having a galvanometer go nuts is unlikely enough, but having both go nut, and by the same amount, would be a tragedy ! LOLAlso... I do have a box full of power resistor (ceramic, glazed, wire-wound...) which I salvaged as a kid 20+ years ago. Never did much with them, but looks like they could be put to good use here ! I could try and find suitable enough to act as a current shunt, and then read the voltage drop across it using my Fluke. That would give me a measure of the current way precise enough, to be able to tell where the truth is !I am currently looking for cheap-ish meters to measure currents as you said, something simple and rugged but reliable and well built and designed, and affordable. I set my heart on the Fluke 70 series. Had a look at the specs. Seems the there is the 73/75/77(23), with accuracy ranging respectively from 0.5%, then 0.4 and 0.3 for the 77. So I am on the look out for these meters. But find one in good condition AND at a decent price AND which comes with it's holster is not as easy as I thought... so the search continues.This one is nice, but at 100 Euros/100+ USD, I am out ! :-/https://www.leboncoin.fr/outillage_materiaux_2nd_oeuvre/988990358.htmHowever this week I spotted a MX53C on ebay, which does come with it's holster (hence, a decent tilting stand to actually be able to use it on the bench...), with a very reasonable starting price... but we all know that bidding can skyrocket in the very last few minutes, so I ma not holding my breath, it will probably end up at a silly price and I will have to back off. But who knows, so I keep an eye on it anyway, can't help, just love those meters so much ! LOLAnyway, enough talk. Time to get back to the bench and do the above mentioned tests, and report ! See you later....

author: retiredcaps
author_rank: Super Contributor
timestamp: September 01, 2016, 05:07:18 pm
content: Quote from: Vince on September 01, 2016, 02:06:27 pmI recognize the limitations of the Fluke 187 wrt to its resistance measurements. I just chose it to give more resolution, not necessarily accuracy. I don't have a 4 wire ohm meter.QuoteI find fuses and capacitors also make good filler items to meet the minimum for free shipping. It is like I always need 1000uF 16V capacitors when I'm fixing things.QuoteWhen one clock says 10AM and another says 2PM, you need a 3rd one. Since we do not have the equipment in front of us, remote troubleshooting, time zone differences, etc prompts these questions.QuoteThe above would also work.QuoteOn ebay.com, these regularly sell for less than $50 USD. Shipping to your country could be expensive though. Alternatively, you can ask on the buy/sell subforum here if anyone wants to sell their Fluke 70 series?

author: ModemHead
author_rank: Frequent Contributor
timestamp: September 01, 2016, 05:08:09 pm
content: It is not uncommon to have current shunts in a "stack" with the 10A shunt at the bottom. The input is injected into the stack at various places to select the shunt value. Any unused shunt resistors at the top become part of the high-impedance voltage sense line.I can't make complete sense of the schematic. It appears to show 5 switch positions, when there is only two actual current range positions. "Z1 ARC1" appears to be a CMOS bilateral switch of some sort, but not sure of the exact layout of the switches. AUX1 and AUX2 are the select lines. IN2 is the voltage sense. (All guesses.)This is one of those designs where it is difficult if not impossible to probe the device while it is operating. I hate that. Anyway, I ran 1.000A through the unit here and measured the voltage drop on the shunt at 4.811mV. Seems like it should be closer to 5.000mV, but in any case the 5390 display reads 00.999A. It makes a huge difference where you measure this, I choose the bottom of R43, and the large screw-hole pad, which appears to be connected to the lower Kelvin point of the shunt. I presume the strange UFO symbol on the schematic at that point means analog ground.It seems your best bet to provide a known current to the DUT for testing is measuring voltage drop across an external shunt resistor. Be aware that the resistance of that shunt will change as it gets hot.

author: ModemHead
author_rank: Frequent Contributor
timestamp: September 01, 2016, 05:17:48 pm
content: Quote from: retiredcaps on September 01, 2016, 05:07:18 pmI do have a 4-wire meter, and from the jack pads, it measures 0.028 ohms. The fuse/fuse-holder has higher resistance than the shunt...

author: Vince
author_rank: Super Contributor
timestamp: September 01, 2016, 07:23:43 pm
content: OK ! Sussed it out finally !Big thanks to RetiredCaps ! The unlikely indeed happened ! It was the PSU's galvanometer reading garbage !I first tried with my old kit/toy multimeter fromwhen I was a boy... goes only to 1A max, but that was enough to convince me, as the MEtrix also showed 1.0 A !So then in order to get more data points, I search my stock of ancient salvaged power resistors... sure enough I eventually found something suitable : 0.47 ohms wire-wound resistors, 6 of them no less. No power rating on them, but compared to similar ones which had markings on them, it's safe to say they must be rater at 5W minimum, most probably 6 or 7.3+ amps, around 0.5 ohms, 5+ W.... teh resistor is just withing spec power dissipation-wise ! So should do it ! But to be really on the safe side, and keep them from overheating which could increase their value and false the measurement, I decided to parallel 5 of them so as to get around 0.1 ohm, which has also the benefit of allowing for easy reading/direct translation of Volts to Amps.So I soldered them together, so as to get a good connection between them, and measured the drop with the Fluke, whilst having the Metrix in serie displaying the current. Before running the test, of course I measured this 5 pack of resistors, using the Metrix since it has better resolution and accuracy than my little Fluke : it reads spot on 0.10 ohms ! Happy enough with that ! :-)Unfortunately the crappy connections of the crocodile clips made the apparent resistance be little higher, so the drop was a bit higher than a one to one ratio. Still, once I processed the 7 data points I took, it was obvious that the reading was reliable : the effective shunt resistance (ie, with the leads and clips), was a very consistent : 0.117 / 0.118 ohms. So there is no doubt that the shunt worked just fine and therefore the experiment was valid.So... the 10A range of the Metrix reads in fact just fine ! .... sorry for chasing a read hearing ! But boy, this galvanometer was all I had to test the Metrix's 10A range.... thought that would work just fine ! Should have done this shunt thing right from the start then !But stil, what the hell happened to my PSU ! Been working just fine for the past 25 years, and now all of a sudden the current display reads garbage ?! Suspicious... might have an idea to what may have caused this : when testing the Vdc range, I put the two (floating of course) outputs in series, so I could go/test up to 60V rather than just 30V. Did the same thing then, to test the 10A range : I paralleled the two outputs, hoping to get 5 to 6A instead of just 2.5 / 3A.I remember that it didn't go too well : the current needles didn't quite do what I expected them to do, and the current display on the second output, would stay to the floor no matter what.So.... I fear I must have mad some damage in the PSU by paralleling them... but boy, I thought all these such dual output floating lab supplies are all meant and designed to be put in series or in parallel, no ?! :-/Luckily, if I don't parallele them, taken independently, tehy still work fine : the vltage can be set just fine as it should, between 0 to 30, and the Volt needle reads just fine. So the problem seems to be limited to the current display... but this is just a galvanometer with a wire shunt bolted right across it's terminal, along with the wires. So... I don't know. I guss I will have to take the two galvanometers out, and wire up some test circtuit on the bread-board, to test them. Galvanometers are very sensitive of course, in the order of 100uA for full deviation, but it should be alright now that I know the Metrix works just fine. It can mesure down to 0.01 uA, so plenty sensitive enough to test the galva, see if either the galva itself has suffered and/or if it's the shunt at its back... or some damage on the PCB of the power supply, at worse...Attached a few piccies of the PSU, vintage chauvin-Arnoux stuff, that's my "2 minute tear down" ! LOLOK ! So now I guess my meter is just fine and just need some TLC ! ... which I will dispense in the coming days, and put it back together., and hopefully everything will be alright then.Someone, a silent read of this topic apparently, private message me saying he owns a MX 55C and was interested in the schematics. I hope I won't go to jail but... I find it so frustrating and unfair not to share the stuff with the few who know and like these meters ! So here it is attached... just don't "broadcast" them all over the web please... let's just keep it contained here. I think if Metrix really cared about the privacy of this stuff, they would not have taken the risk to give it to me (never mind in easy to spread PDF form !) in the first place ! Or at least they would have explicitly told me what their policy was... but they didn't do any of that. So... hope you enjoy as much as I do !Thanks again for the advice and tips you gave me to help me figure it out, I much appreciate it !

author: Vince
author_rank: Super Contributor
timestamp: September 01, 2016, 07:30:28 pm
content: Oops, forgot to put some photos, I like picciesHere, pics of my little toy/kit meter I built when I was little. Still, I like the looks and feel of it. Scale looks nice, and nice rubber housing that does a great job at bouncing the thing all over the bench. Then a pic of it side by side with the Metrix : 1.00 A on the Metrix, and my analog meter reads just a tad under full scale, so really not bad for what is really nothing but a toy !

author: Vince
author_rank: Super Contributor
timestamp: September 01, 2016, 07:38:10 pm
content: Hell, can't believe I had THAT many power resistor... that's the opportuniy to organize them a bit ! The carbon film ones, the glazed/vitrified ones (not sure how you call them in English), the wire wound types, plain, and then the really vintage one, wire-wound but hollow, for better cooling I guess. Then the ceramic ones.

author: Vince
author_rank: Super Contributor
timestamp: September 01, 2016, 07:42:13 pm
content: ...

author: Vince
author_rank: Super Contributor
timestamp: September 01, 2016, 07:55:39 pm
content: Now I have to fix the PSU... tear down time !The two output are really completely distinct. They have their own PCB, and both boards are strictly the same. Transformer has two taps : 30V of course, and a middle tap at 15V with a relay to switch between the two, so that the PSU can lower the power transistor's dissipation when the outputs is set to a low voltage but draws lots of current.Each of the outputs have the following connected to their terminals/jacks : a diode (BY550, will look that up. drop tested at only .45V, lower than your usual diode eh ), then a 47uF electrolytic cap, and what looks like a "MOV" ?! Then, there are 4 very high value resistors, (they wouldn't even measure with the fluke), connecting each of the 4 terminals/jacks, to the chassis/earth connection.You can also see the current shunt bolted right accord the lower galvanometer's terminals.The boards use the classical at the time uA 723 ... I guess these days there more modern/better replacements. Each board/output actually uses TWO uA 723 ?! Don't know what the second is for ? Constant current regulation maybe ? Could be, because on the PCB, we can see what looks like long wire shunt, that runs alllll along the edge of the PCB, see it ? So could be used as a current sense to perform the current regulation ?!That was my impromptu 2 minute tear-down, a la Dave, sorry if I lack the talent !

author: Vince
author_rank: Super Contributor
timestamp: September 01, 2016, 07:57:51 pm
content: ...

author: retiredcaps
author_rank: Super Contributor
timestamp: September 01, 2016, 09:21:04 pm
content: Quote from: Vince on September 01, 2016, 07:23:43 pmGlad you got it working. Everyone on the thread contributed to make it working.

author: Assafl
author_rank: Frequent Contributor
timestamp: September 04, 2016, 10:55:29 am
content: Got to love R2 in the power supply!

author: Vince
author_rank: Super Contributor
timestamp: September 04, 2016, 06:10:55 pm
content: Quote from: Assafl on September 04, 2016, 10:55:29 amWell yes, kinda stands out eh ?! I don't know why they needed to make that shunt wire sooooo long. Who knows. To help cooling/accuracy maybe.. though accuracy is hardly a concern in the design of this particular PSU for sure. So don't know.Anyway how, I have just validated my ordered at Farnell, to get the bits I need to finally put the Metrix back in one piece. However sadly, the order will be delayed because of the 28 pin LCD header connector, as it comes direct from the manufacturer's stock. They state a delay of 5 working days, so at best, if I am lucky, I will get the parts on Saturday morning. So in the meantime, I will work on trouble-shooting and hopefully fixing the PSU.Since this topic is about tearing down the Metrix, I guess the schematics I uploaded are in line with this topic and that deserve some comments as part of the tear down, no ?I see that dozen or so people have downloaded it ! So it must be of some interest to some people, more than the few of us who actually post in this topic anyway.So... what could we say about this board/schematics ? I spent a few hours reading the m again and again...Overall, it's more complex/convoluted that I thought it ought to be ! To start with, the representation of the contacts/tracks of the main rotary switch, is not so easy to understand... one can eventually figure out the broad lines, enough to get a sufficient understanding of where the signals come and go... most of them anyway, but saying that I understand easy and every little detail of it, would be rather presumptuous...Anyway. The main thing that I find interesting, is the overall architecture of the thing. You have got the big "DMM5" proprietary chip on the main board, and the little LCD board with a big chip on it, and a header connector linking the two. So, one would assume that it's all very classic an arrangement : the DMM 5 chip has got to be the main processor doing it all, and it just talks to the LCD board to control the display, and the chip on the LCD board is obviously the LCD driver. Right ? No, totally WRONG ! LOLLooking at the schematics, one quickly sees that the big DMM5 chip handles only the analog stuff, doing most of the magic. The main board actually is 100% analog. The LCD board is actually the main digital board, everything digital is all happening in there ! The LCD driver is actually not the driver, it's the main processor/controller, a modest 4 bit MCU from NEC, featuring 16KB of PROM (in my meter anyway, a 316 version, not the 308 / 8KB version pictured in the schematics), 512 bytes of RAM, and running at around 4MHz.So, it's completely upside down compared to most other meters I would guess. That little LCD board contains everything digital, and the main board and that DMM5 proprietary chip, are completely dedicated to handling all the analog stuff. So, a very clear separation between analog and digital. I guess this helps achieve the high accuracy of this meter, by keeping away the fast digital transients, from "polluting" weak but precious analog signals. Well, just a supposition... after all, there are many meters in the MX series, hence sharing this same basic architecture, yet most of them are hardly precision instruments. But maybe Metrix being a fairly small company after all, couldn't afford to design 20 different architectures for each and every of their instruments, so they invested their R&D money in something that would be suited to the most accurate of their meters, then all the less accurate ones would therefore also benefit from it.The LCD / digital board_______________As we have just seen, it's actually not just the LCD board, but the main CPU board. Besides the LCD controller, the MCU doesn't integrate very much in terms of peripherals, just the bare minimum to be able to operate the meter : a couple 8 bit timers, a serial interface so it can handle the external Cal EEPROM but strangely it is not being used, the pins are used as general purpose pins, so chatting with the cal EEPROM has got to be implemented in S/W... why... and a few digital I/Os to handle the membrane keypad, RS232 IR link to access the outside world, and a few more input lines to get the status of the Fuses and position of the rotary switch (using 4 lines, " ROT0 " up to " ROT3 ".And of course, the data bus and usual associated control lines, so it can control the DM5 chip to get back the readings from the DMM5 built-in ADC, and also drive the 3 and only digital lines featured by the DMM5 chips (labeled "AUX 1/2/3" ) in order to select ranges and enable or disable the 10M input resistor on the mV range, according to what the user is asking for in this regard.The MCU actually does not feature an UART (the serial interface is just for simple SPI links and the like). The TX and RX signal are then tied to general purpose I/O pins. The link must then be implemented in software, which might be why, I would guess, the CPU runs at a rather fast almost 5 MHz, which would otherwise be unnecessary I think (?), to operate this meter. At any rate the DMM5, which is connected to the data bus of the MCU primarily to send back the results of its internal ADC, runs from a modest 32+ KHz watch crystal !The LCD board also includes the backlight circuitry, for those meters who do have it (not my vanilla MX55 anyway). It's totally independent from the MCU, so should the MCU fail, you would still be able to turn light on and off. It uses a TLC393 comparator (comparator of choice throughout this meter) to H/W debounce the membrane button, then goes to a couple D flip-flops (usual 4000 series CMOS) to perform the toggling action. The LED backlight is then driven by a discrete transistor.Check Fuses : once again, a clear distinction between the analog part of the detection circuitry, which is on the main board, and the digital part of it. So, the digital board gets the analog feed from the main board, and adds a little bot of shaping circuitry so it can apply it to the digital IO pins of the MCU. In the case at hand, a couple comparators are sued for FUSE1 (TLC 393 as always), and a third being used for FUSE2.The Cal EEPROM : an ST 93C46 ( 461 actually on my meter). NOthing special you say ? One point worth noting though : they are not rated at the usual 10 year data retention period, but a surprisingly high, and much more suited to the task... 40 YEARS ! And the C461 I actually have in my meter, is rated at 100 years ?! Dear... didn't know such EEPROMs even existed ! So I found that interesting.Size-wise, it hold only 128 bytes, so just enough to cram in the required cal data.The main / analog board____________________So, that big DMM5 chip, to start with. It's main purpose is then to assist in implementing all the analog magic required to put the meter together. It embeds teh ADC and sends its readings to the digital board via the CPU(s 4 bit data bus).It houses the buzzer functionality, said buzzer is connected straight to it. Might be why it is scratchy/not latched... the chip being so analogy in its design, I guess a latch was not in order.It features a current output which goes straight to the input jack. Of course this is used when in ohms mode, or capacitance or diode test.In order to produce accurate(ish) current for the various required ranges, it uses an external 3 pins 1.25 voltage reference, along with a little cascade of carefully calculated resistors.It has a digital input dedicated to measuring frequency. Being digital, the signal passes first through some external shaping circuitry, in the form of a couple comparators, yes, TLC 393 again...The precision/potted divider network is connected straight to the DMM5 pins.... along with no less than 12 capacitors ! Boy what the hell do they all do. The 3 trimmer caps found on the board, are actually all part of this bunch.There are quite a few analog inputs and output on this DMM5, sometimes a bit hard to follow. Signals come in, then out, then in again via some other door... its a bit hard to follow I admit. From what I can gather : two signal come from the "front-end" of the meter/ input circuitry : "PR" and "10M". 10M as its name suggests, goes to the highest/10M tap of the precision network. PR attacks it from the 1M step just below.From that, the DMM5 generates several other signals : "AN0" , which is then sent to the shaping circuitry which produces a clean digital signal which is fed back to the frequency input of the DMM5.The DMM5 also output a couple more signals : AC1 and AC2. These feed a couple things : the RMS converter, and a "discrete"/improvised 10 bit DAC made out of a binary counter (a 74HC4040), coupled with a 10 stage/bits R-2R ladder, as you do... but whose goal escapes me, any idea ? These two signals are then fed to an analog switch (a classic CMOS 4052 chip), whose output, labeled AC3.. is then fed back to the DMM5 ! See ? signals just keep going in and out of this DMM5 chip ! LOLThis analog switch is actually a double switch, and serves a second purpose : switching R25 on and off, the 10M input resistor, in order to be able to obtain a super high impedance mode when using the mV range.The DMM5 has 3 main analog inputs : IN1 to IN3. IN1 is the one used to read DC voltages, through the precision divider network. IN2 is the input used to measure currents. IN3 is used I think when measuring ohms or capacitance or testing diodes : the DMM5 outputs the current to the jack/into the DUT, then reads back the resulting voltage via this IN3 path. In the path of this signal, is a complex network of no less than 12 resistor... which really make up for a simple two resistor voltage divider, as you can see. But I guess it was necessary to put several resistors in series to get the high voltage protection a single tiny SMD resistor had no chance to meet. A similar arrangement is used nearby, by another circuitry in the front end : a chain of 5 resistors to make up for one high-voltage item. said resistors drive a rather complex arrangement of 5 bipolar transistors.. though their final goal is clearer : they drive a FET that shunts the input jack. Probably used to discharge capacitors once they have been tested ? Something like that...As for the section related to current measurement, it has been already described in a previous post. Basically the signal goes through a ladder of shunts, and an analog switch taps it where necessary, for the required range, then the signal is sent straight to the "IN3" in put of the DMM5, without any further processing. Switch control inputs are driven directly by AUX 1 and 2, 2 of the 3 digital I/Os the DMM5 features. Obviously, again, the DMM5 doesn't even know what it's doing... it merely drives this pins blindly, ordered by the MCU sitting on the LCD board. The DMM5 merely passes on the orders...The current ranges are switch by an analog switch bu sadly it a proprietary Metrix-ITT switch, so not data sheet available. but well, its operation doesn't seem to hold much mystery. The terminals being labeled on the schematics, and being rather self explanatory. Just a switch. 4 inputs controlled by two digital lines, "AUX"' 1 and 2, which come directly from the DMM5 chip, and which are remotely controlled by the CPU on the LCD board via the data bus.Well that's all I can think of. At any rate that give me a good enough understanding of these MX50 series meters, so I feel confident to buy some more, as I know how they work and could potentially fix them is need be.So that is it, the tear down is now complete I think !

author: Vince
author_rank: Super Contributor
timestamp: September 08, 2016, 09:08:12 pm
content: Hi again ! Sorry for inundating this topic, I think I am almost done now... because today I just put my MX 55 back together, and it feels much better now, so I will call it a success.I have not yet received the 28 pin header connector for the LCD/digital board, but decided to reassemble it anyway, because I figured replacing the connector would be took great a risk : the pads on the PCB are round and really tiny, so little copper there... so I think leaving my bodge wire, which works just fine, is doing much less harm than damaging the tiny pads on the PCB, at best, or ending up bricking my meter at worst....Farnell sent me all the other stuff I required though, so no worries : a few 10M 1% resistors, Vishay no less, a can of IPA and a couple of anti-static brushes (a soft one and a "tooth brush" stiffer one).So, I replaced that 10M resistor.. and realized stupid me, that I ordered a 500mW one but the original one was only quarter what.... luckily it still fits.Then I cleaned the golden tracks of the rotary switch... couldn't get it 100% because it appears a bit worn out so can't do much about it (is there "liquid gold" available, like there is "liquid tin" to tin PCB tracks ?? could be interesting.) However, looking at the before/after close-up pictures I took, it's undeniably much better than it was, so well worth it.Then I sprayed the entire PCB with IPA, both sides, to give it a good clean with the soft brush... a clean PCB being essential when dealing with high-impedances/low level signal. Couldn't hurt I thought.Then I soldered the RF shield back on.Then I tested it... and it works so much better, I am happy camper ! :-)In the mV range, my ears feel much better : now the alarm screams only when "expected to", in the high impedance mode that is. But in the regular 10M mode, no alarm no matter how much I play with the test leads. It reads 0.XX mV like the Fluke.The capacitance mode is back to its former self as well, very happy with that : now it behaves perfectly. After a reading/measurement (real or fake, with open or shorted leads), the display does'nt "float" randomly or erraticly displaying "Run'. No, as soon as you remove the capacitor, the display goes back instantly to a solid/steady 00.00nF ! Great ! :-DOh, and ths week I bough a couple MX53C to complement the 55 ! :-) One of them is NEW ! Bought in 1999 by a guy at his work place, for teaching purpose... never got used. When he left work for retirement, he took it with him... and after a few years decided to put it up for sale. BRAND NEW ! He opened the case merely to take a pic to illustrate his ad, but other than this.. this meter quite literally never saw the light of day ! So the foam is like new (not discolored and still very firm, a set of spare Ferraz fuses, manual, and even a full page of calibration data from Metrix, for all ranges !such a joy.So, with this "reference" meter at hand, I could better test/compare with my MX 55, to validate my repair. Everything is fine then. Capacitance wise, they are within 1% of each other from 47nF right up to 6800uF. Also, I checked of course the main 10A range, again by shorting my lab supply, and boy I was not disappointed.... up to 1A about, the match was perfect right down to the LSD ! And at 3.5A or so, the max deviation between the two was only 3 or 4 LSD !I also couldn't help but make the two meters test each other : the MX 55 in ohms range, connected to the 5C3 mA range. The 55 was then measuring the value of the current shunt (the value being actually high enough to be measurable in the mA range), and the 53C measuring the precision/calibrated current output by the 55. See picture below... the two read just perfect ! On its 5mA range, the current shunt of the 53C reads the expected 100ohms, and teh current output by th 55 to measure the shunt, is bang on the the expected 1.0uASo... looks like my 55 has now a clean bill of health. Behaves well, reads true... I now consider it a reliable meter I can use with confidence in my project.The new 53C came with a holster.... at last I have one ! Well, if you don't have one.. GET one. Really makes it so much more usable : no fear of dropping or banging it on the bench, features the indispensable stand so you can actually see the display without having to get up your chair to look at it from above... and it is very rubbery-anti-slip, you can actually operate it with one hand, be it the knob or even inserting or disconnecting the leads.So, really, it makes the meter much more pleasurable to use on the bench, I find.What about my other 53C ? It stands right at the other end of the spectrum, relative to the new one. I picked it up on Ebay France/locally, starting price was only 20 Euros so I kept an eye on it... thinking that as always the bidding would skyrocket all of a sudden, 5 minutes before the end of the auction. So I was not holding my breath/ But somehow, turned out there was only one other bidder, and I won the auction ! It was mine for only 46 Euros ! :-D So even less than half the price of the new one (100 Euros). Obviously, for that price, the pics on Ebay looked like it was in a very sorry state, and until I got it in my hands, I was kinda prepared to have wasted my money. But... after I dismantled it and gave every part a thorough cleaning and loving care... and replaced the leaky battery and cleaned the corrosion on the battery terminal, and put two new ceramic fuses (bought a 10 pack for each range the other day)... it turned up actually REALLY nice, so a great buy indeed, very happy ! It took came with the holster too ! :-DSo i have kinda a little collection of MX50 series now ! Love them ! I intend to buy some more... as dave said "you can never have too many multimeters ! " LOLThe MX55 will be my main meter, the most accurate one, and the 53C will be there to supplement it when I need to keep an eye on several measurements at the same time.. or just as a backup. Their 0.1% is still plenty good enough for what I do or intend to do, and that's 3 to 5 times more accurate than the Fluke 70 series I am fancying too, not to mention 50,000 counts versus 4,000, a larger display, more functionnality etc.... yet they cost the same amount, at least of here ! around 80 Euros plus or minus 20 Euros depending on condition. So really, regardless of my love for theses MX50 series, the cold facts are also on my side : for 80 Euros or so, the choice between a Fluke 77 and a Metrix MX 53C is a no brainer I find. At least for bench work, which is teh goal. For a general purpose meter you put in you tool box and use to work on your car or around the house or anywhere to do whatever.... I would prefer the Fluke 77. smaller/more nimble, a bit ore rugged I feel, and easier to operate with one hand, and better protection if it does (?) have the same huge HRC fuses that the 87V has. So I might still buy for this purpose, to complement my fluke 11 which is perfect for this kind of use but.... which doesn't measure current sadly ! And also it doesn't get as much use as voltage measurement, there had been occasion where I really needed to measure current...Anyway. I tore down this well used 53C apart, and noticed a few things which might be of interest to this tear-down topic, so I will end with this.First things I notices, compared to my 55, was the the RF shield is not soldered to the back of the PCB anymore, but rather replaced by a foil glued to the back cover. So, nothing get in your way when you want to access the back side of the PCB, like I needed to. There is a little spring soldered to the ground plane of the PCB, which make contact with the foil/back cover.Then, I noticed that the LCD header connector was a different type : mine which I broke a pin off of, was the very fragile round and thin terminals. the 53C on the other hand, had the much more robust beefy square type. now way I would have broken a pin, had my 55 had that type of connector ! :-/But the most interesting, was that.. horror... when I was presented with the back side of the PCB, I instantly noticed something very wrong ! It was unpopulated !Alll the stuff related to RMS measurement was gone ! The AD converter itself, the "home made" 10 bit DAC, and the analog switch that feeds the RMS result back to the DMM5 chip. And the top side of the PCB... some more stuff is gone : the current shunts for the mA range, and the analog switch that taps them !Still, the 53C is an RMS meters just like all the 54/55/56 of course, so... this tells us something new about the DMM5 chip : it must have a built-in RMS converter, as well as current shunts and analog switch for the various mA ranges.... but that the performance of the DMM5 chip in these department was not deemed good enough by Metrix to achieve the accuracy they wanted so the added their own external circuitry to remedy this.Looking at the spec sheet for the 50's series, which someone posted toward the beginning of this thread, it all become more obvious : the 53C is not just bottom of the range for it's lesser 0.1% basic accuracy, no it also has worse specs than the 54/55/56 for current measurement accuracy, which indeed confirms that it must uses some built-in circuitry from the DMM5 chip, and it also has lower RMS bandwidth than all the others in the series, yet again confirming the DMM5 having a built-in, but poor, RMS converter.So here you go, we learned a little something more about this DMM5 chip, even though it's a proprietary black box.So... at first I though well, maybe these 53C aren't such a good deal after all... but really I think they still are. I mean the RMS features is a selling point but honestly, I can't think of a use for it for lab/design work, the accuracy, crest factor, and piss poor bandwidth renders them rather useless I find, in practice, what do you think ? In practice, it's DC voltages I am interested in, as well as the other features the meter offers. If for some application I have to actually get a half decent RMS measurement of a signal, the only option I guess is to use a digital scope. It's got the bandwidth, and the crest factor is not an issue either, since it can calculate the RMS on any arbitrary waveform : if it can trigger on it, it can display, and if it can display it, then no matter what the the shape of the signal is, it can compute the RMS value equally well. I think this RMS feature on hand-held meters is very useful for measurement on the filed on electrical system/industrial stuff, motor control, what have you, but as an accurate way to measure electronic signal of any frequency and any shape and crest factor....So.... I think these 53C meters are still well worth "collecting" to complement a more accurate 55/56 meter, for when you need more than one meter at a given time. I have spotted a couple more of them in excellent condition for 80 Euros each, in the local ads.. might be tempted ! LOLI didn't think they would (relatively) so easy to find. The 54/55/56 are much harder to find. Came across a brand new 56 the other day, for 160 euros.... so excellent value for money I find, but sadly it was already sold, stupid seller didn't bother removing his ad, like so many other sellers, who just don't care wasting prospectives buyer's time ! grrr.... drives me nuts.The 53C has one thing for it though, over my 55 ! It can measure duty-cycle ! I tested on my ancient Philips analog function gen. Duty cycle is not adjustable, but still, wanted to see it would read. No disappointment there : bang on 50.00% !!! Well, half of the time. Every now and then it would wander a bit, but always in a window of 49.9 - 50.1, so pretty good, for such a basic and old function gen !I find this DC feature quite nice... it's simple enough to implement, that one can actually trust the value displayed by the Metrix, and I think it could come very handy when checking or designing anything using PWM signal, so quite a useful feature I find. Keeps from having to hook up a digital scope ! Much more convenient to use the hand-help meter I find.Sorry for a long post again ! But well, somehow I found it at home here, hope I didn't annoy to many people. Well at least I managed to get the schematics and share there here, so a decent contribution to this topic I reckon :-)A few piccies and that will be it. Thanks again to everybody who helped me in fixing my MX 55, now working just fine.Below pics ::- Farnell shopping : IPA, anti-static brushes, Vishay 10M 1% metal film resistors, packs of ceramic fuses suited to the MX 50 series, a couple tiny chisel tips, with built-in temperature control, for my 30+ year old 24V AC Weller iron... can't believe Weller still sells this model of tips ! That's customer support for ya !- before/after pics of the golden tracks, using IPA and the anti-static brushes. not quite perfect but much better none the less.- The bodge wire for the header connector will remain for now...

author: Vince
author_rank: Super Contributor
timestamp: September 08, 2016, 09:14:26 pm
content: - Got it wrong, original 10M was only 0.25W.... but I ordered an 500mW one, oh well, can't harm I guess, and it still fits in the enclosure so all is well.- That Weller PCB stand came in quite handy to solder the 10M resistor on to the board.- Soldering the RF shield back on.

author: Vince
author_rank: Super Contributor
timestamp: September 08, 2016, 09:18:41 pm
content: - Now we can put the meter back together again at last- the 55 and 53C checking each other...- The 53C measuring duty-cycle spot on from the old function gen.- A complete and brand new MX 53C, with full calibration data and still the protective strip on the LC window, what more could one dream of ?!

author: Vince
author_rank: Super Contributor
timestamp: September 08, 2016, 09:25:10 pm
content: Mini comparative tear-down of the 53C vs the 54/55/56 :- soldered RF shield replace by a foil in the back cover- all the RMS related circuitry has disappeared from the back side of the main board- as well as all the current shunt and analog switch of the mA ranges, on the top side of the PCB.- potted precision network/divider had been replaced by a more modern ceramic substrate as we commonly find on the Fluke meters- Quite a bit of corrosion on the negative terminal of the battery, but it cleaned up just fine, the PCB lower down, was still in good shape.

author: Vince
author_rank: Super Contributor
timestamp: September 08, 2016, 09:27:43 pm
content: Is it possible to have TOO MANY MX50s meters ?! I don't know... Aren't they cute, keeping each-other warm ?! :-)I just happen to really love them ! LOL

author: retiredcaps
author_rank: Super Contributor
timestamp: September 08, 2016, 11:22:16 pm
content: Quote from: Vince on September 08, 2016, 09:27:43 pmI hope your weekend is free because I'm curious why your 53C doesn't support Hz and Surv like my BK 5360?PS. Modemhead did all the modifications, without schematics too, on this meter.

author: retiredcaps
author_rank: Super Contributor
timestamp: September 08, 2016, 11:34:09 pm
content: Quote from: Vince on August 28, 2016, 08:03:41 pmTurn your Fluke 11 into a Fluke 12 as well thanks to a tip from Excavatoree.https://www.eevblog.com/forum/chat/fluke-25-my-first-digital-multimeter/PS. Your 55C has some pads that might work?

author: Vince
author_rank: Super Contributor
timestamp: September 09, 2016, 05:15:53 pm
content: Quote from: retiredcapsOh, H/W hacking on multimeters ! I personally wouldn't want to hurt/damage the original looks of the meter, but I am curious none the less : is there a topic on here detailing these mods he did on you meter ? What does this "surveillance" feature do ?BTW I don't understand why you say my 53C doesn't support frequency measurement, as obviously it does ? Your rebadged one too it sems, I see the little yellow "Hz" symbol on the front panel, just like on mine. Frequency measurement works just fine... so not sure why you added a second Frequency button ? What does it do that the built-in Freq measurement doesn't ?QuoteHats off to him for reverse engineering the required portion of the meter.. but I hate going blind, it's limiting and time consuming, I am sure he would have used the schematics if he had them available at the time, unless this was some kind of reverse engineering challenge in its right of course !Although I don't want to damage the case by doing hand modifications to it, I still like the idea of H/W so long as it's invisible from the outside, or S/W hacking and... actually I am thinking of a little something that I would like to try : I hate the screeching sound of the continuity tester... to me it really makes the meter feel like a crappy/cheap unit, which of course it is most definitely not ! So I am thinking of playing with my second 53C, the one I got for real cheap, to see if I can modify it to get a latched sound. Since the 53C has quite some board space available due to the unpopulated RMS and mA ranges stuff, I guess it could be possible to put some small SMD 74XX logic device and a few passives around it if required, to get a nice latched sound, whilst keeping the fast response of course.Thanks for the link from Excavatore ! Interesting about the Fluke 10 series ! He says these meters are very prone to developing "black blobs" on their LCD... mine surely does ! I always felt guilty about it, thinking I might mistreated it somehow, but maybe I am not at fault then !Still, doesn't keep it from working just fine, that's the most important.Excavatore also makes me feel much better now, too : I was starting to feel guilty and silly for "collecting" a handful of old Metrix 5X... but I see he has around FIFTY units of a GIVEN Fluke model ! So even more if you add all the various models he has ! So, I now feel almost "normal" in comparison ! LOLLearned about the existence of the 76/79 models too, which are improved /later revisions of the 75/77 which I was fancying, so I will start chasing the 79 instead of the 77 ! LOL But prices seems way above what their specs command : found a couple on Ebay, for 100/120 Euros (say 120/150 USD or about), same price as MX55/56 or so, or my immaculate/brand new 53C. So it would be unreasonable to buy one at this price :-/ For 50 or 75 buck though, I am in.More generally I am happy to see that I am not alone in being "crazy"/very fond of old meters, and "collecting" them.... I don't feel as strange or lonely any more, thanks guys ! LOLThis latching mod sure will be one of my little winter projects/experiments !

author: retiredcaps
author_rank: Super Contributor
timestamp: September 09, 2016, 08:04:07 pm
content: Quote from: Vince on September 09, 2016, 05:15:53 pmRobomeds was the first to discover that the BK5360 extra pads actually work by pressing them. No hardware additions/modifications needed at all. That is, the functionality is already built in (just like the Fluke 10 and 11). You just have to find something to press the contacts.The Hz and Surv are described in the manual as shown in the attachted picture. More detailed info is in the manual if you want to read more.QuoteHe also has an ebay guide for buying Fluke meters.http://www.ebay.com/gds/Fluke-Meters-Main-Read-First-/10000000007231862/g.htmlFor the 70 series info seehttp://www.ebay.com/gds/Fluke-Meters-Models-and-Series-main-/10000000007478323/g.html

author: Vince
author_rank: Super Contributor
timestamp: September 09, 2016, 09:22:54 pm
content: Oh ! Sorry if I appeared a little retarded, I got it for the Fluke 10 series, but didn't for the Metrix !Thanks for the info then. The surveillance mode doesn't seem quite useful for an electronic lab to me, however this "Herts" feature sounds really great indeed ! :-D Still no way I am going to perform surgery on the case, however I am now well willing to spend some time hunting for an MX55/56 'C' to complement my vanilla 55, so I can play with this Hertz featureWill probably take some time though, the 53C appeared very easy to find (or maybe I just happen to be searching at the right time and am lucky), however the more accurate/expensive 54/55/56, never mind the revised/later 'C' versions, are much rarer to be seen ! But I shall persevere of course !The 54/55/56 'C' are also the only ones to feature a backlight apparently ! So that's an extra motivation.Thanks for the links to the buying guides from excavatoree ! Never heard of this "buying guide" pages on ebay ! Probably US only, as Ebay US is so much bigger than the individual smaller ebay site we have here in Europe, each country having it's own one, due to language and different laws etc...This excavatoree gentlemen appears to have a really very severe "fluke" disease eh ? A good thing though, hats off to him for collecting so many Flukes ! Impressive indeed. I will make sure to take the time to read all the wisdom he dispenses there !Now lets try and play with this Hertz feature on my 53C !

author: ModemHead
author_rank: Frequent Contributor
timestamp: September 09, 2016, 10:10:09 pm
content: The mods don't require any reverse engineering, just a little mechanical hacking. The buttons are made from an old TV remote and some scrap plastic.

author: Robomeds
author_rank: Frequent Contributor
timestamp: September 13, 2016, 03:43:57 am
content: I believe the surveillance mode can function like the Fluke touch hold. You hold the button until it beeps. At that point it will record a stable reading and beep to let you know the reading has been recorded.

author: macboy
author_rank: Super Contributor
timestamp: October 09, 2017, 02:08:34 pm
content: The full version of the SX-DMM software package, which is compatible with these ASYC-II (ASYC2) meters, is now freely available for download at the manufacturer's website. The file you are looking for is "sx-dmmv2.9_0.exe" (or possibly a later updated version) and is found at the DMM support page at:http://www.chauvin-arnoux.com/en/support/telechargement/results/dmmYou will also find some LabView and LabWindows drivers there.I just noticed also that the meter is recently supported by SigRok (as of December 2016). The MX-56C is explicitly listed as supported, hopefull other models work too since the protocol is the same (though not all functions are supported by all models).https://sigrok.org/wiki/Metrix_MX56CUpdate: seepost belowfor updated calibration software that works with newer versions of Windows.I will also once again post a link to the calibration software for these meters. This is a direct link to the B+K Precision website. They sold re-badged versions of these meters with model numbers 5360, 5370, 5380, 5390. This software is compatible with all ASYC-II meters AFAIK.http://www.bkprecision.com/downloads/software/AK5350.zipA serial interface is needed for the any of the above software to talk to these meters. Of course they sold an expensive hardware kit to accomplish this, and of course it is long discontinued even if you did want to buy it. Luckily the interface is simple, just a UART at 2400/8/N/1. The physical interface is a IR LED and phototransistor inside the battery compartment. I used a USB-TTL serial interface (any one will do) and used a pull-up resistor and phototransistor on the Rx side, and a IR LED with resistor to Vcc on the Tx side (TTL level UART idles high, not low). You may need to reassign the COM port of your USB-UART to 1 through 4, then simply point the software to that COM port and it should work. You need to hold the "PK +/-" button while turning on the meter to enable the RS-232 interface.The serial protocol is fully documented, in several languages, in a file calledNF-SX-ASYC2.pdf.I normally don't necro-post, but since this thread has become the definitive source of knowledge on this multimeter series, I decided it was the best place for it.

author: Vince
author_rank: Super Contributor
timestamp: October 09, 2017, 02:55:23 pm
content: Thanks a lot for all this Macboy !I haven't psote on here for a year or so, but have not been inactive on this front though :in the mean time, I bought literally a dozen of these meters !!!I just can't enough of them !I did see an MX 56C in his carry case in like new condition AND in the case was... the serial cable/adapter and the raised front panel that goes with it... a gem... couldn't believe it ! Sadly it sold in an eye blink and I arrived to late....

author: macboy
author_rank: Super Contributor
timestamp: February 07, 2018, 03:58:10 pm
content: Direct links to latest version of calibration software, compatible with x64 Windows (tested here with Win7 x64). The previous version linked in above posts is a 16-bit Windows application, so it won't work with anything newer than 32-bit Win XP.http://www.filiale-de.chauvin-arnoux.com/sites/default/files/download/sx-asyc2cv23.ziporhttp://www.chauvin-arnoux.com/sites/default/files/download/sx-asyc2cv23.rar

author: Vince
author_rank: Super Contributor
timestamp: February 07, 2018, 04:09:15 pm
content: Thanks for the updateI ought to build a serial cable one day, and start fiddling with all my MX53/54/55/56 meters.. because hell, I just love these meters, it' s officially a disease of mine now, bought a dozen of them in a short time, couldn't help...

author: sergej
author_rank: Contributor
timestamp: February 22, 2024, 10:10:06 am
content: Hello all.I post photos of internals of my MX 56:

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 23, 2024, 12:41:52 am
content: Are you repairing a broken via here?

author: sergej
author_rank: Contributor
timestamp: April 22, 2024, 01:16:13 pm
content: Noooo :-)I use this wire to safely recognize the vias on the other side of the PCB.