Author Topic: Extech EX420 (Read 12236 times)

bazsa56 · « **on:** April 20, 2015, 01:59:09 pm »

Hi!

Been reading the site and watching the videos for a while now, however I only decided to register today after receiving the Extech EX420 in the mail. I watchhed Dave's video of the EX330, seemed like a nice meter, so I ordered the 420 cause I wanted a seperate input for current measurement and I wanted the backlight. Anyway, after placing the order I saw some of the quality issues with the Extech meters here on the forum, so after receiving my meter first thing I did was open the thing up.

Sure enough, my meter is not without issues.

I attached some pictures of the PCB, as you can see the bottom side where the switch is has a nick at the bottom and the traces are a bit scraped and the top side has a wire soldered on the board acting as a via! What the heck is that? Funny thing is, I don't think those traces are supposed to be connected. I can't see any damage other then the nick at the other side, so why is that even there?

I did a few measurements with the meter, voltage seems okay, haven't tested current, however resistance measurement is off by a bit. Testing the leads itself measures 2.7 ohms! Measuing 220 ohms, sure enough the meter is off by 2-3 ohms compared to other meters. Pretty pissed off about this.

It's a shame really, costruction wise the meter seems decent, strong, would probably survive a drop without issues, but yeah, this is probably my first and last Extech meter...

Note: sorry about the crappy quality of the pictures, took it with my phone, might get around to posting better ones during the week...

RoboTechEd · « **Reply #1 on:** April 20, 2015, 06:16:34 pm »

Quote from: bazsa56 on April 20, 2015, 01:59:09 pm

I did a few measurements with the meter, voltage seems okay, haven't tested current, however resistance measurement is off by a bit. Testing the leads itself measures 2.7 ohms! Measuring 220 ohms, sure enough the meter is off by 2-3 ohms compared to other meters. ...

DC voltage will almost always be accurate regardless of meter. Cheap Harbor Freight freebies will be good enough for most DC. When it comes to resistance though you should be able to be a bit more accurate I would think. You should have an option to zero out the probes. To do this, hold them together and wait for the reading to settle. At that point click the REL option on the meter. This will compensate for the probes. I have an Extech430 as my primary and use aftermarket probes (thank you radioshack bankruptcy) that have higher than desired resistance as well. This is what the REL function is designed to compensate for.

I also have an issue with my displays backlight. It has TERRIBLE viewing angles. Was curious if you have the same issue with a EX420?

bazsa56 · « **Reply #2 on:** April 20, 2015, 07:23:20 pm »

Yeah, I know about relative mode, but still, 2 ohms seems a lot for the probes. I get something like 0.1-0.15 for the same probes on another meter.

Viewing angles with the backlight on aren't too great for me too. You can see barely see the display when viewing from above the normal viewing angle. Not that big of an issue though...

RoboTechEd · « **Reply #3 on:** April 20, 2015, 07:31:04 pm »

Quote from: bazsa56 on April 20, 2015, 07:23:20 pm

Yeah, I know about relative mode, but still, 2 ohms seems a lot for the probes. I get something like 0.1-0.15 for the same probes on another meter.

Viewing angles with the backlight on aren't too great for me too. You can see barely see the display when viewing from above the normal viewing angle. Not that big of an issue though...

Ah okay. Yeah I agree that is quite high for probes. My radioshack ones were about 2 ohms as well, surprised me a lot at first too...I wonder if that is affecting other measurements now that I think of it...

And yeah the viewing angle of mine is poor from below mainly. If I use the kickstand at desk level, I almost cannot see the screen while sitting. Its absurd. I likely won't be getting an extech either. I should tear mine apart and see if the construction is similar to yours

retiredcaps · « **Reply #4 on:** April 20, 2015, 08:28:43 pm »

DId you buy this EX420 as new or used? If new, those tracks sure took a beating and those shorted probe readings sounds suspicious.

New probes should measure around 0.1 to 0.3 ohms. At 2.7 ohms, either one or both of your probes could have a bad/loose connection? Even the crappest test leads that come with the cheap 830 that fall apart measure around 0.8 ohms.

You can try to narrow down which one may be bad by putting one probe into the COM and the tip of that probe into the V/ohm jack. Note the reading for the one probe. Then do the same for the other probe.

Alternatively, you can try a different pair of probes in the EX420 or use the EX420 probes in another multimeter.

I'm not surprised at the internal bodges and sloppiness.

BTW, CEM Instruments makes a lot of EX series multimeters for Extech. The tall exaggerated digits is a sign of their design.

Lightages · « **Reply #5 on:** April 20, 2015, 08:47:40 pm »

More atrocious build quality from Extech re-branded CEM made multimeters. Thanks for adding your experience to the growing list of junk from them. I am surprised that Extech still sells this crap. I guess this says something about their concern for quality. On the other hand the MM series from Extech is made by Brymen and is top notch, but not that much more expensive than the EX crap.

Send it back and get a refund. It will fail and it will be a loss of money. Buy something better so you don't have to worry if your meter is actually working correctly or not.

Edit: added the word "expensive" to be clear

Grapsus · « **Reply #6 on:** April 20, 2015, 09:31:24 pm »

I bought an EX430 a few years ago after seeing the teardown of an Extech 300-something which looked well-built. It works ok and is still within spec, but the construction inside is sloppy too, it has some resemblance with OP's multimeter, but less awful. I can take pictures if someone is interested. It cost me 70 euros. Now that I know that Brymen and used Flukes can be had for the same price, I would never buy an Extech again, ever.

RoboTechEd · « **Reply #7 on:** April 20, 2015, 09:40:22 pm »

Quote from: Grapsus on April 20, 2015, 09:31:24 pm

I bought an EX430 a few years ago after seeing the teardown of an Extech 300-something which looked well-built. It works ok and is still within spec, but the construction inside is sloppy too, it has some resemblance with OP's multimeter, but less awful. I can take pictures if someone is interested. It cost me 70 euros. Now that I know that Brymen and used Flukes can be had for the same price, I would never buy an Extech again, ever.

I agree, when at my bench I find myself using my Fluke8012a over my 430. It seems to be more accurate and have much higher build quality, despite being from the 80s

retiredcaps · « **Reply #8 on:** April 21, 2015, 01:21:54 am »

Quote from: Grapsus on April 20, 2015, 09:31:24 pm

I can take pictures if someone is interested.

Yes, please.

lowimpedance · « **Reply #9 on:** April 21, 2015, 05:45:33 am »

Has the resistor below the bodge wire been cut and then 'tacked' back together !?!.
POS, as suggested send it back and invest in a better meter.

bazsa56 · « **Reply #10 on:** April 21, 2015, 07:57:27 am »

I got the meter brand new from conrad. The meter was in the voltage measurement position out of the box, not in the off position.

Did some further measurements, the probes now measure between 0.5 and 0.8 ohms. Pretty weird, it takes a long while for it to measure (auto ranging is slow) and it fluctuates a bit between the 2 values. I don't know, I guess the probes might not have made proper contact, but I could reproduce the 2.7 ohm measurement yesterday several times. Still not quite happy with the fluctuation...

Using the same probes on 2 other meters I get 0.1 ohms without any fluctuation.

I'll test current this afternoon.

The funny thing about that resistor bridging is that I can't figure out why is that needed. The traces don't seem damaged around it and judging by pictures I've seen of other EX4xx meters, that connection is totally unnecessary!

retiredcaps · « **Reply #11 on:** April 21, 2015, 06:24:47 pm »

Quote from: bazsa56 on April 21, 2015, 07:57:27 am

I got the meter brand new from conrad.

Return it for your money back.

bazsa56 · « **Reply #12 on:** April 21, 2015, 08:00:53 pm »

Did some testing with the current measurement features.

I used a resistor that I measured at 2120 ohms (with 3 seperate meters) and tested it with my bench psu and a uni-t ut61e.

At 5 volts I'm supposed to measure ~2.35 mA.

The extech measured at 2.223 mA, well off spec.
The uni-t measured at 2.317 mA, much better.

Did the tests at 1 volt as well.

Supposed to get 471.6 uA.
extech measured: 445 uA
uni-t measured: 475 uA

So basically the extech is off by about ~5.5%, well off the +-1.5% + 3 digits spec mentioned in the user manual. Even one of my OneHungLow branded 10$ meters was closer to the actual value then the Extech. The extech does start falling in spec above 10mA.

Anyway, I don't do too much testing like this most of the time, so if I made some sort of obvious mistake I'd be happy if someone would point it out, but right now to me it seems like the Extech is well off spec and I'll try returning it or exchanging it.

I might be able to get it replaced with the Amprobe AM-510 or the Extech MN47. Any opinion on these? I'd rather get the Amprobe unless someone has some bad experience with it, I don't think I'll ever touch anything Extech branded ever again.

RoboTechEd · « **Reply #13 on:** April 21, 2015, 08:16:24 pm »

Quote from: bazsa56 on April 21, 2015, 08:00:53 pm

So basically the extech is off by about ~5.5%, well off the +-1.5% + 3 digits spec mentioned in the user manual. Even one of my OneHungLow branded 10$ meters was closer to the actual value then the Extech. The extech does start falling in spec above 10mA.

Those look way out of spec. I measured my Extech 430 in the post below and found everything to be within spec (although not perfect). Sounds to me like your unit is defective

Link to test data/discussion:
https://www.eevblog.com/forum/testgear/lab-calibration/msg656771

retiredcaps · « **Reply #14 on:** April 21, 2015, 08:22:02 pm »

Quote from: bazsa56 on April 21, 2015, 08:00:53 pm

I might be able to get it replaced with the Amprobe AM-510 or the Extech MN47. Any opinion on these? I'd rather get the Amprobe unless someone has some bad experience with it, I don't think I'll ever touch anything Extech branded ever again.

It looks like the Extech MN47 is another CEM rebrand/variation of this meter (see pictures). I wouldn't necessarily stay away from Extech, but rather CEM Instruments. With that in mind, this phrase, "fool me once, shame on you, fool me twice, shame on me" comes to my mind.

Amprobe doesn't make any of their own meters either. Their meters were either acquisitions from Meterman or Beckman. Or they sell rebranded Appa Technology and Brymen meters.

Teardown pictures AM-510 or its siblings are here on eevblog, but it is unclear to me who the original manufacturer is.

https://www.eevblog.com/forum/reviews/amprobe-am-530-a-peek-under-the-hood/

bazsa56 · « **Reply #15 on:** April 21, 2015, 08:30:21 pm »

Quote from: retiredcaps on April 21, 2015, 08:22:02 pm

Quote from: bazsa56 on April 21, 2015, 08:00:53 pm
I might be able to get it replaced with the Amprobe AM-510 or the Extech MN47. Any opinion on these? I'd rather get the Amprobe unless someone has some bad experience with it, I don't think I'll ever touch anything Extech branded ever again.
It looks like the Extech MN47 is another CEM rebrand/variation

Yeah, I'll be staying away from that one then.

Anybody know who makes the AM-510? It seems decent enough, I think I'll sleep on it and decide in the morning. I might end up paying a bit more and get something better...

EDIT: I started the process of sending back the Extech POS, once I got my money back I'll buy something else. Meanwhile I've decided to spend more money and get something proper, so right now I'm eyeing the Amprobe AM-270 and the Brymen BM257s. Any opinion on these? They both seem really good from what I've read on these forums and on the internet. I also checked the teardown video Dave did of the Brymen BM257, looks pretty good.

Lightages · « **Reply #16 on:** April 22, 2015, 12:57:23 am »

The BM-257s is a better meter IMHO. The AM-270 is very good though too although the back light is a horrible joke.

Grapsus · « **Reply #17 on:** April 22, 2015, 01:02:42 am »

Quote from: retiredcaps on April 21, 2015, 01:21:54 am

Quote from: Grapsus on April 20, 2015, 09:31:24 pm
I can take pictures if someone is interested.
Yes, please.

Here you go, I just posted them in a new thread.

Lightages · « **Reply #18 on:** April 22, 2015, 01:13:36 am »

Basza:

www.tme.eu has a number of Brymen meters. The BM829s is a really good all round meter if you want to step up from a BM257s. If you want internal logging of 80000 records at up to 20 times per second, then the BM525s is the one. If you want the ultimate Brymen for accuracy, then BM869s. I have all of them and I also sell them here in South America. I started selling them after I had such great experience with Brymen

bazsa56 · « **Reply #19 on:** April 22, 2015, 02:07:04 pm »

I just returned the meter, my money's gonna get transfered back in the next 2-3 days. Once this thing is done I'll get the BM257s.


EEVblog® Main Site	EEVblog® on Youtube	EEVblog® on Twitter	EEVblog® on Facebook	EEVblog® on Odysee

Author Topic: Extech EX420 (Read 12236 times)

Share me