Metrix MX407 megohmmeter - Quick teardown and repair. - Page 1
Forum section: electronics / testgear

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 15, 2018, 12:44:20 am
content: New meter arrived the other day, bought cheap and not working once more.(Paying the price for working equipment takes the fun out of it, and is not worth the bother half the time, as things come with problems even when sold as working...)It was was making a rattling sound so I didn't turn it on, I took it apart.Found a loose melf diode floating around, a close look made it obvious where is came from, et voilà! Another working meter in the heap.Now the downside: Metrix was one of the reference brands for meters in France, they have since been bought out by Chauvin-Arnoux who still sell Metrix and Multimetrix branded meters.Metrix / Multimetrix seem to have been moved down to the low-end, the Chauvin-Arnoux being the serious stuff. (I wish someone would review / teardown the Metrix Scopix III handheld scopes here!)The build quality of this megohmmeter is just way under what I was expecting from Metrix, clearly a Chinese job, the "QC" sticker was on the back but components drop-off the PCB from being only half soldered.The ADC is a GC7135, equivalent to the ICL7135 but there again, a little deceiving, as it is the cheap far-east copy.The PCB is marked "Meiyad" just under the transformer so possibly none of the design is done by Chauvin-Arnoux at all.

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 13, 2019, 02:52:42 pm
content: Self-updating as usual...This meter is the same as the AEMC 6527 model.The PCB manufacturer "Meiyad" also made the PCB's in at least some "Klein Tools" DMM's.

author: threephase
author_rank: Regular Contributor
timestamp: January 13, 2019, 09:53:18 pm
content: That's intriguing, Meiyad is the same marking on the PCB for the Extech MG302 and DiLOG DL9307 insulation multimeters that I have been playing with.I believe that these are really the DT9985 manufactured by CEM.

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 14, 2019, 08:31:54 am
content: Your two meters are definitely the same model.If Meiyad are a PCB manufacturer no doubt they'll have their stamp on quite a bit of kit, I'd just be curious to which company(/ies) they work with and who actually designs things before they are X,Y,Z branded.Overall the design isn't awful, it's just under what I'd expect for gear in that price range.I ended up selling the MX407, I've kept a British made (Megger) Newlec NLINS3 and a Fluke 1520 as insulation meters.

author: tekn95
author_rank: Newbie
timestamp: April 30, 2019, 11:31:09 am
content: Hello everyone,I am looking for references or zener zener z2, z3, z5 for my mx407 if someone can help me.thank you

author: tekn95
author_rank: Newbie
timestamp: April 30, 2019, 11:34:23 am
content: or their characteristics

author: on4top
author_rank: Regular Contributor
timestamp: May 01, 2020, 11:20:47 pm
content: Hello ,I bought the same meter at HamFest in 2019 .It also has issues ... diode burned of and plastic melted ..Also Q15 was dead .. replaced it with BD139 .D12 looks to me like a standard diode .Z5 is a zener .. but what value .. i have no clue .The meter works on Voltage .But on ohms only shorting works ..After replacing Q15 the high voltage seems to work again ( when i measure using a DC meter i get the 3 voltages ) ..But no Ohms are measured .. i did nog put another zener in .. also the pads on the pcb are broken ( i tryed gluing )Ofcourse nowhere to find any schematics ... really would like the correct values of Q15 / Z5 and maybe other zeners .The MOV's on the therminals and PTC's are fine .. which suprises me ..https://photos.app.goo.gl/TGmnqBsRm47FXFfTAAnyone can help me with values of components ?RegardsTomBelgium

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 01, 2020, 11:24:10 pm
content: I'll be of no help here, this meter was sold long ago now, I don't hold on to equipment when I don't like the internals

author: on4top
author_rank: Regular Contributor
timestamp: May 02, 2020, 12:00:14 am
content: Thanks for reply .. i bought it verry cheap knowing that is has a fault ..It sure is Chines inside .. not really worth 3-400 euros ( Conrad / Rs Components )I'm 1 step further .. Z2 was dead shorted and now the Ohm meter is working / Voltage DC working also ( worked already )Also the Megaohm works ..But Z2 and Z5 is now missing .. so i guess something will be missing ..So hard to figure out the value of and SMD ZenerRegardsTom

author: on4top
author_rank: Regular Contributor
timestamp: May 02, 2020, 12:01:47 am
content: https://photos.app.goo.gl/4HCNicBXjxNgtuvB6https://photos.app.goo.gl/Y2sFt5qknHe2xmRq5

author: on4top
author_rank: Regular Contributor
timestamp: May 02, 2020, 04:56:36 am
content: Z3 seems to be a 12V zener diode .I removed it and made al smal test-setup .Z5 and Z2 are now removed and the meter seems to work ..https://photos.app.goo.gl/cREkBAY4zNpfV5qQ6Sad we don't have schematics ... Z5 and Z2 must have a reason .With Z3 removed measuring ohm is broken .The question now is what is the value of Z5 and Z2 .. also 12V ..or someting else . ( they all look the same those SMD Zeners )

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 05, 2021, 10:58:08 pm
content: I just repaired another of these with a suspicious (as in fake-looking) 2SD882 transformer primary switcher that had fused open without signs of heat, cracks or craters.In case the values of Z2 and Z5 are needed they both test in the 28-30V range @ 2mA.I made a quick test setup too...Edit: Added photos.There's nothing that smells NEC about that transistor...

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 19, 2021, 02:47:16 am
content: Having found a few more MX407's to repair, removing the rear PCB to clean switch contacts I noticed that the front PCB was marked "CA6527".Funnily there is no Chauvin-Arnoux branded 6527 sold in Europe the 6527 is an Americas only AEMC model.

author: Breizh13
author_rank: Newbie
timestamp: June 26, 2022, 02:01:10 pm
content: Hello to everyone on this thread, from France.I also bought this MX407 on a flea market, for not much. I had been looking at it with the intention of getting it to work, then it sat in a drawer for a long time.Turns out it's the same components that are burned, Z5, D12 and Q15.Did anyone finally find the values for Z5 and D12. For the transistor, I saw that it was a 2SD882. I'll be glad to read you again with the hope of bringing this device back to life.--Philippe

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 26, 2022, 03:14:15 pm
content: Don't know about D12 but not zener, worth checking reverse voltage in circuit or going for a 1kV blocking model.Z5 is 28 or 30V zener I doubt it matters much.