Teardown: Extech MN16A Autoranging DMM

[schwarz-brot]

There we go! Santa brought a brandnew Extech MN16A and of course the first thing I am going to do is TEAR IT APPART!

Again I am going to do this in Parts. This is

Part 1: The outside


Pic 1: Overview of the contents of the package

Picture 1 shows what you get: A nice looking tiny DMM that looks funky. Some cheapish testleads and a Type-K thermocouple with adaptor for the input jacks. You see right - my blister was missing the manual. Are you kidding me, Extech? All this comes in a simple blister-pakaging. Nothing fancy but ok. The manual can be downloaded. This is no issue but somehow gives that special kind of feeling when you have your first look at your new product and start to realize this is not as good as you expected it to be.


Pic 2: Overview front


Pic 3: Overview back


Pic 4: Overview standing

The meter itself has a large display. It can be read very well from all angles (Picture 2). Whats missing is a backlight, but I am ok with that. The softbuttons give a nice feedback and do not feel wobbly. The switch turns nicely with a good click between positions, this feels well constructed. It feels a little tiny on the other hand, you could for shure not turn it with heavy working gloves. Also you would then for shure miss the softbuttons as they are pretty close to each other.
The back sports a plastic stand that feels very cheap, nothing else (picture 3). This means, there is no rubber that would stop the device from sliding around while working. The integrated rubber on the case is soft but not extruded far enough to stop this thing from sliding. One can also see there are only screws. That means you have to unscrew the thing to switch batteries or fuses.
The stand in action is seen in picture 4. I am shure this will break with the first fall from my bench.

I have not worked with this unit yet. But I checked the continuity tester. It is a very fast one but sounds very crappy - it is not latched. The autoranging feels somehow slow.
Since there is only one off position and the Ampere-ranges are placed from the lower to the higher ones one has to go through "the unsafe way". I dislike that.
The case itself feels very sturdy. Not a brick like the previous Tenma DMM but pretty stable. I also like the built-in rubber parts. For sure they won't help as much as the big holsters on other meters but better than only plastic.


Pic 5: Overview testleads


Pic 6: Detail testlead


Pic 7: Detail testlead: Tip without cap


Pic 8: Detail testlead: wire

The testleads are simple ones with a cheap look and feel but proper safety connectors  (picture 5). They are rated CAT III 1000V / CAT IV 600V (picture 6). If the cap is taken off (see picture 7) the tips they show a CAT II 1000V rating. Length is about one meter (not measured).
Again I had trouble taking a proper picture of the writing on the wire. It says: "AWM 1803 E199279 VW-1 80°C 18AWG 2000V LEO HUI" for the red one and sports the "RU"-logo.


Pic 9: Closeup tip

Take a deep breath and then look at picture 9. Yepp. It's the tip of one testlead. Anything but sharp. I am tempted to say this is safe enough to be a kids' toy. One bit more and it would have been a spoon. Rubbish!


Pic 10: Overview thermocouple


Pic 11: Detail tip thermocouple


Pic 12: Detail adaptor thermocouple

Last part to take a look at for today is the thermocouple (picture 10). It is a standard type-K one with about 120cm length (again, not measured). The isolation seems to be proper glasfiber. But they decided it should look good and put heatshrink-tubing over the end of it. Why?! Therefore this can only be used up to 300°C/572°F. I never saw such a big blob on a welded thermocouple as can be seen in picture 11, not sure about that. More important is the adaptor seen in picture 12. This allows to use standard off the shelf thermocouples with this meter which was one of the most important things when I decided it had to be this one.


This is it for today, next time I will unscrew the meter. Again, your comments, requests, suggestions kind and not so kind words are welcome. I need your feedback to do better!

See you,
Jan

[schwarz-brot]

Part 2: The inner goods


Pic 13: Detail of screws on back


Pic 14: Overview with opened battery compartment


Pic 15: Detail unreachable fuses

In this part I am going to unscrew the Extech MN16. If one has to change batteries the compartment has to be unscrewed. This is done with two nice screws (those silvery ones in picture 13). They go straight into metal inserts (see picture 15). Nothing to worry about.
The back of the battery compartment can then easily be lifted off, the screws stay in it and won't get lost. Nice. The batteries are standard AAA-types, original brand "Greenergy". Whatever... (Picture 14).
One is also supposed to take only this cover off to change the fuses. But take a look at picture 15 - there is no way to get the fingers in there. Even with a tool it will be hard to do. This is bad constructed!


Pic 16: Detail of the screws holding the back


Pic 17: overview with opened back.


Pic 18: Detail of blast protection

Therefore one will decide to take off the back. Unscrew the four black screws and find no more metal inserts. Just cheap self-tappers (Picture 16).
Once opened, the back sticks to the front (Picture 17) - the batteries are connected by soldered wires. Not that well constructed. Also see that picture to get a feeling of the size of this device: the batteries are size AAA. Yepp, it IS small. And there is no metal shielding on the back.
 With the case opened the blast protection can be seen. It is the typical solution with an extruded wall going into a deep groove. The size looks ok to me (Picture 18).


Pic 19: Detail model number on silkscreen

Last thing to mention at this stage of destruction is the printed model number on the silkscreen: "MN16B." (Picture 19). The device was sold as MN16A. Hmmm, whatever.


Pic 20: Detail of the screws holding the PCB

Taking out the PCB is a bit tricky. One has to loosen 5 screws (Picture 20). The three ones with the broad head are easily identified. But the other two are not self-explanatory. One has to chose the ones on the top edge of the PCB, the other four hold the display protection in place.


Pic 21: Overview frontside of the PCB


Pic 22: Detail of the large display Protection


Pic 23: Detail Softbuttons

The front of the PCB shows some very nice gold plated contacts for the switch, the softbuttons and the display with its protection (Picture 21). This protector is a very sturdy one, the display cannot be stressed in any way, I like it (Picture 22).
The softbuttons are one big custom made rubber piece (Picture 23). This feels solid and fits nicely into the front panel. The contacts also look well.


Pic 23: Detail spring contacts

In the top half of the case the rotary switch is built-in. I did not bother to take that apart. But I took a picture of the nice spring contacts (Picture 23). Nothing to worry about.

Next time, you'll get the rest of the beauty. Stay tuned.

[Lightages]

Thanks for the teardown, but could you show more detail on different parts of the circuit board and around the input jacks and components in the next images?

It is nice that the fuses are accessible without opening the whole case.

[Flenser]

I'm looking for one of this style multimeter.
What is the current drain?
How does the diode test function handle displaying the voltage for red/green/blue leds?
[Found the manual online and answered this myself: Diode Test - Test current of 0.3mA typical, open circuit voltage 1.5V DC typical]

[schwarz-brot]

Hi there, this is

Part 3: the PCB
of the Extech MN16 Teardown.


Pic 24: Detail Input section seen from bottom


Pic 25: Detail Input section seen from top


Pic 26: Detail Input section seen from side.

The input section shows no magic (Pictures 24 to 26). It seems to be well constructed and laid out. The large cutouts for the jacks fit into extruded plastic tubes in the top of the case wich for sure will suppress any arching. The high current paths are very large and also there is additional solder on them. This seems to be able to handle any high currents one wants to pass through this small meter. The fuses on the other hand are only the small ones but seem to be HRC-Types (That was the word, right?).
There are some Movs and most devices are larger SMD types that seem to be able to handle some power.
What I clearly dislike is the construction of the jacks themselves: There is only one post going to the PCB and in the back half of the case is no support underneath the jacks. This means every time one puts the connectors in or takes them out, the single solderjoint is stressed. Bad, bad...
Also, the very large soldered areas do not all look well. As if the termal mass of the area was too high to get a proper soldering.
Also, can anyone tell me, what the large blobb of solder on the shunt is good for (Picture 26)?


Pic 27: Detail main IC seen from bottom


Pic 28: Detail main IC seen from above

The main chip cannot be identified, sorry folks (Pictures 27 & 28). But one can clearly see which screws have to be taken out to rip out the PCB. Also one can see lots of trimpots. I wonder if this meter can be calibrated to do better than the poor ratings stated in the manual.


Pic 29: Detail of operational amplifier section from top


Pic 30: Detail of operational amplifier IC


Pic 31: Overview of operational amplifier section from the other side

There is one TI chip that I suspected to be an ADC (pictures 29 to 31), but in fact it seems to be an operational amplifier. I did not dive into this section any deeper, go figure it out yourself if this is of interest.


Pic 32: Detail battery wires

Picture 31 shows also the connection of the battery: The wiring goes through the PCB to be soldered on the top then. Maybe to take some stress out of the connection, or maybe they decided it would be more easy or cheaper to solder it on that side. Who knows. But then take a look at picture 32... just one more addition to the cheapish look and feel.


So for a conclusion... I don't really know.
This meter gives lots of functions that may be nice to have in many situations. But the accuracy is too bad to make it a good solution for any special task. I feel this is a good allrounder to have on your bench but no specialist by any means. For example, if there is a load of capacitors to be sorted the capacity funktion will serve you well, but if you need to know what capacity one capacitor really has you better look out for a more accurate device.
The 10A range is a plain joke: "For 30 sec. MAX every 15 min.". Well, large fuses are expensive... What the hell am I supposed to measure with such a device?!
I cannot get rid of this "that's just a toy" feeling. I have not worked with it yet, therefore I cannot say how it does in the daily routine.

I would clearly not recommend this meter to anyone who wants to have a robust meter for everyday use. There are better cheap ones out there for this requirement. In this case I would suggest a very basic but robust meter with only the most basic functions, if it has to be very cheap.
On the other hand this was one of the cheapest devices I could get with autoranging, which was important to me, and the option to take a standard thermocouple. Also I had no devices that gave all those bonus-functions: I had no possibilities to check capacities, frequencies (ok, my scope, but that is overkill most of the times), temperature and I wanted a relative-function as well. Since I have a basic robust meter, I only needed a cheap addition that also gives some more bonuses along the way. And this is the only situation in which I would recommend the Extech MN16: As addition to an existing meter and only if you can get it very cheap and only occasionally need those bonus functions (and have no other device that has them).

[Bored@Work]

Also, can anyone tell me, what the large blobb of solder on the shunt is good for (Picture 26)?

That's the adjustment of the shunt. It had a bit too high resistance so they added a bit of a parallel resistance to a part of it.

Would the shunt have been too low they would have nipped a dent or a few dents into it.

[retiredcaps]

Thanks for another great composed and clear set of teardown photos. I enjoyed reading your comments and hope to see more in the future.

[Lightages]

Thanks for the thorough teardown. You might be undecided what you think of this meter in the end but too me it doesn't appear to be too bad a buy. I am biased against Extech so I was surprised to think that you were being a little harsh. The input protection actually looks right for its CAT rating and for a general use meter I would not be worried about its safety.

[james3]

I would clearly not recommend this meter to anyone who wants to have a robust meter for everyday use. There are better cheap ones out there for this requirement

I was going to buy this meter, buy I would like to consider other ones of same range price, Could you be so gentle to tell me which DDM should I consider too ?

thanks for your review, it was really accurate