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Metrix MX56C / BK Precision 5390 Multimeter Teardown

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Vince:
@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 !  :D

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 ! LOL

It's so cool !   :D

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 !  :) :) :) :D :D :D ;D ;D ;D

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 !  ;D

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.

Performa01:

--- Quote from: Vince on August 31, 2016, 01:53:28 pm ---@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.

--- End quote ---

Well, 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.

Vince:
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 !....

retiredcaps:
On the BK5360, I get using a Fluke 187 with leads relatived out

100.84 ohm on 5mA range
10.51 ohm on 50mA range
1.54 ohm on the 500mA range
0.03 ohm on the 10A range

retiredcaps:
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?

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