Products > Test Equipment
Metrix MX56C / BK Precision 5390 Multimeter Teardown
Robomeds:
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.
Robomeds:
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.
Robomeds:
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.
Robomeds:
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.
Amarbir[Lynx-India]:
Well,
I Love These Meters ,Very Solid And If There is a Fight In The Lab you Know what i Am Talking About ;-)
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