Author Topic: Extech MM570A video review and teardown photo's  (Read 20425 times)

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Offline Spawn

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Extech MM570A video review and teardown photo's
« on: January 22, 2013, 07:48:26 am »
Extech send me a MM570A as replacement for EX570 , but is it better?

It certainly is! What a huge difference, the overall quality and workmanship on the PCB is a lot better.

My video review here:


Meter itself is a lot faster than EX570, continuity test is Fluke like. Update speed is good, protection is well taught and the fuses are a lot better.

You think I am Extech fan now? Well you got it wrong here comes the downside, backlight has 4 LED’s behind the LCD instead of like on any given multimeter in the corners, so you see 4 LED's in your screen and it is butt uggly. The backlight has auto power off after 30 seconds, and you can’t change that, so every time you turn on the light it goes off after 30 seconds, they say it is for better battery life, who cares about the battery when I turn on my backlight, I just want my backlight lit and nothing else and I will be the judge of when I want to turn it off. These two things are not that huge problems, so not end of the world but slightly annoying.

The other thing which made me worry was, even when I told them that I will take photos and test than put it on the forum, the LCD screen was full finger prints not outside, no on the second screen in the meter, here comes the grand final… the 440mA fuse was blown out of the box! I mean, come on Extech, we are talking about quality control last couple days on EX570 these two things are not even that big problems to locate.

At the end, do I like the meter? Yes despite the problems this meter is just other league than EX570, is it equal to Fluke? Nope but close to it, and it should be because a US Fluke 85-V cost almost same as this one in US, not here in Europe because we pay for 85-V twice more than in US and the extech is slightly more expensive than US. But Fluke won’t send you a meter with full finger prints and blown fuse… so if you like finger prints and blown 10 dollar fuse in your meter, by all means go get Extech.

So should you buy one? I would say, if you live in US get the Fluke and if you are in Europe and don’t have the money for Fluke go for Extech. Even better, go for Brymen because it is a lot cheaper…


So if someone from Extech is reading this, don’t bother to mail me because I won’t bother to mail you either.  You got me little disappointed with the finger prints and got me really pissed with blown fuse. I am sending back EX570 this week, have fun with it…

As for the photos, here they are, judge yourself guys :)









Size difference:





















« Last Edit: January 23, 2013, 08:05:44 am by Spawn »
 

Offline iloveelectronics

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #1 on: January 22, 2013, 07:59:19 am »
It is a rebadged Brymen, albeit an older design (their new ones all have the curvy BM-867/869 shape). The "BTC" on the main chip is a dead giveaway, it stands for Brymen Technology Corporation, all the Brymen leads are branded BTC too.
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Offline Spawn

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #2 on: January 22, 2013, 08:06:24 am »
Yeap I know  :)

That's why I said:
Quote
Even better, go for Brymen because it is a lot cheaper…

Offline retiredcaps

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #3 on: January 22, 2013, 08:53:14 am »
The other thing which made me worry was, even when I told them that I will take photos and test than put it on the forum, the LCD screen was full finger prints not outside, no on the second screen in the meter, here comes the grand final… the 440mA fuse was blown out of the box! I mean, come on Extech, we are talking about quality control last couple days on EX570 these two things are not even that big problems to locate.
Hear that?

Someone at Extech is probably  |O and/or  :palm:.
 

Offline Lightages

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #4 on: January 22, 2013, 09:25:44 am »
Not only does this reflect on Extech, but also on Brymen as the OEM.

I have no complaints on the construction and cleanliness of my BM869, but I a a little peeved on the included leads. At leat they are not bad leads, just what I did not expect.

So I wonder what will Extech do now?
 

Offline Wytnucls

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #5 on: January 22, 2013, 10:01:27 am »
It seems to be the Brymen MB859CFa in disguise:
http://www.brymen.com/product-html/cata850a/BM850a_Catalog.pdf
 

Offline Nermash

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #6 on: January 22, 2013, 10:20:58 am »
I have a strong feeling that you received refurbished/repaired/ex-demo unit from Extech... I don't know a lot about Brymen QC, but I don't think that Bussmann or Siba let bad fuses go out from the factory?
« Last Edit: January 22, 2013, 11:39:26 am by Nermash »
 

Offline jnd

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #7 on: January 22, 2013, 12:20:52 pm »
What is the AD chip on right in the 9th photo? I can't read it but it looks like some reference.
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Online PA0PBZ

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #8 on: January 22, 2013, 01:38:02 pm »
What is the AD chip on right in the 9th photo? I can't read it but it looks like some reference.

AD636, RMS to DC converter.
(Why can't you read it, reading on your phone?)
Keyboard error: Press F1 to continue.
 

Offline jnd

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #9 on: January 22, 2013, 02:09:00 pm »
What is the AD chip on right in the 9th photo? I can't read it but it looks like some reference.

AD636, RMS to DC converter.
(Why can't you read it, reading on your phone?)

Nope, the SO-8 under it, I should specified that earlier.
Wannabe volt-nut, slowly hunting solid meters with low budget.
 

Offline Spawn

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #10 on: January 22, 2013, 03:04:40 pm »
Not only does this reflect on Extech, but also on Brymen as the OEM.

Lightages, I don’t think this was Brymen but someone who tested the unit before shipping out or like Nermash said it is a refurbished item.

So I wonder what will Extech do now?

I don’t   ^-^ I mean after that many QC issues lately they get a chance to cover that little bit maybe only for me, but I was ready to brag about their customer services and how good they are with aftermarket issues, everything went perfect and fast, till I saw those finger prints and the blown fuse.

Offline Spawn

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #11 on: January 22, 2013, 03:13:08 pm »
I have a strong feeling that you received refurbished/repaired/ex-demo unit from Extech... I don't know a lot about Brymen QC, but I don't think that Bussmann or Siba let bad fuses go out from the factory?

I don’t think it is Brymen’s fault nor the fuse manufacturer, nothing is impossible but I think it went wrong when they wanted to test before shipping out and they didn’t notice, this is only me assuming things I could be wrong of course

@Whtnucls, yeap it is, I didn’t mention in my first post because it is widely known on the forum.

Offline Spawn

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Re: Extech MM570A video review and teardown photo's
« Reply #12 on: January 23, 2013, 08:07:44 am »
Video review added to start post, it is HD but youtube is still bussy, give it a hour for HD version.

Offline retiredcaps

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Re: Extech MM570A arrived as replacement for EX570 but is it better?
« Reply #13 on: January 23, 2013, 08:21:00 am »
I don’t   ^-^ I mean after that many QC issues lately they get a chance to cover that little bit maybe only for me, but I was ready to brag about their customer services and how good they are with aftermarket issues, everything went perfect and fast, till I saw those finger prints and the blown fuse.
Personally, I think you should give them one last chance to make it right.  Perhaps you will get a "new" perfect one this time and they will let you keep this MM570A.
 

Offline Spawn

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Re: Extech MM570A video review and teardown photo's
« Reply #14 on: January 23, 2013, 08:47:04 am »
I doubt that retiredcaps, they suggest to give me a MM560A first I didn’t accept it and ask for MM570A after that they needed two days to discuss about that I think, because mailing was suddenly stopped  ;D

Offline retiredcaps

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Re: Extech MM570A video review and teardown photo's
« Reply #15 on: January 23, 2013, 09:48:12 am »
I doubt that retiredcaps, they suggest to give me a MM560A first I didn’t accept it and ask for MM570A after that they needed two days to discuss about that I think, because mailing was suddenly stopped  ;D
I don't work in the T&M industry, but in my previous field, I made darn sure the customer was 100% satisfied with a new purchase no matter what.  It was this attitude that helped us win the majority of the business even though our products were premium priced.
 

Offline Spawn

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Re: Extech MM570A video review and teardown photo's
« Reply #16 on: January 23, 2013, 03:59:59 pm »
Hmm maybe you are right, the thing is I am afraid to get a multimeter even worse than this one, it’s just how I feel. The finger prints where already cleaned by me when I was taking the review video, and I already put a new fuse in there, other than that this meter is great, it has some good quality unlike EX570

Offline zaoka

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Re: Extech MM570A video review and teardown photo's
« Reply #17 on: January 23, 2013, 07:17:26 pm »
Nice review!!!!  Please review MetraHit 23  if you have time :-DMM

 

Offline Spawn

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Re: Extech MM570A video review and teardown photo's
« Reply #18 on: January 23, 2013, 08:50:07 pm »
Thanks  :) I am not sure how old my 23s is, I got it second hand while ago it is a discontinued model, you will like to see inside?

Offline zaoka

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Re: Extech MM570A video review and teardown photo's
« Reply #19 on: January 23, 2013, 10:49:08 pm »
Yes, many people said thats a good model.
 

Offline nanofrog

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Brymen 857A for comparison purposes
« Reply #20 on: January 24, 2013, 01:11:30 am »
I just got a Brymen 857A from eBay, and tore it apart for comparison purposes.

Please note that there are some differences on the board vs. the model Spawn posted. But keep in mind, that based on the date codes on the unit I have, this one was made in late 2000 - early 2001, and the MM570A from 2011. Quite a few years difference.

Some of the differences:
500V fuses, and in a smaller package (5mm x 20mm), and not as much input protection.
No battery access hatch (must remove the entire rear cover).
2 different semis.
No pots; precision resistor network instead.
Gold plating on all the selector switch contact surfaces (PCB).

Unlike Spawn's MM570A however, both fuses were good.  :P Leads weren't even in a bag, and looked used. Given it's age, this may be a refurb or used in excelent condition (sold as NIB).

 

Offline nanofrog

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Re: Extech MM570A video review and teardown photo's
« Reply #21 on: January 24, 2013, 01:19:48 am »
Internal pics.
 

Offline nanofrog

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Re: Extech MM570A video review and teardown photo's
« Reply #22 on: January 24, 2013, 01:22:44 am »
Last of them.

 

Offline retiredcaps

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Re: Brymen 857A for comparison purposes
« Reply #23 on: January 24, 2013, 01:44:11 am »
Please note that there are some differences on the board vs. the model Spawn posted. But keep in mind, that based on the date codes on the unit I have, this one was made in late 2000 - early 2001, and the MM570A from 2011. Quite a few years difference.
Thanks for sharing the pictures with us.

Having just fixed a 25+ year old Fluke 8060A due to 5 out of 10 electrolytic capacitors leaking its electrolyte, I hope those two electrolytic caps don't leak on you anytime soon.  In Spawn's pictures, it looks like they have been replaced or removed.
 

Offline iloveelectronics

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Re: Brymen 857A for comparison purposes
« Reply #24 on: January 24, 2013, 01:50:59 am »
Thanks a lot for the teardown! It does indeed look quite different from the latest Brymen models. Still seems like super good value for money for the price you paid though!

I just got a Brymen 857A from eBay, and tore it apart for comparison purposes.

Please note that there are some differences on the board vs. the model Spawn posted. But keep in mind, that based on the date codes on the unit I have, this one was made in late 2000 - early 2001, and the MM570A from 2011. Quite a few years difference.

Some of the differences:
500V fuses, and in a smaller package (5mm x 20mm), and not as much input protection.
No battery access hatch (must remove the entire rear cover).
2 different semis.
No pots; precision resistor network instead.
Gold plating on all the selector switch contact surfaces (PCB).

Unlike Spawn's MM570A however, both fuses were good.  :P Leads weren't even in a bag, and looked used. Given it's age, this may be a refurb or used in excelent condition (sold as NIB).
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Offline Spawn

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Re: Extech MM570A video review and teardown photo's
« Reply #25 on: January 24, 2013, 01:52:22 am »
I can see what we talk about nanofrog, it is actually weird they keep same housing and try to improve over the years, mostly these kind manufacturers change the shape of the meter over the years, 10 years difference taught them something and they improved on the newer models it seems, I see some things un unpopulated on your main PCB which are filled on mine like the ones under the shield on my PCB.  It is like Fluke 80 series improving over the years but changes are not much as this one.

You got yourself hell of a meter for that price, it is just great  :-+

Offline rbola35618

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Re: Extech MM570A video review and teardown photo's
« Reply #26 on: January 24, 2013, 02:04:23 am »
I have an Amp Probe AM140 and the inside looks very similar. This leads me to believe that it is also a Brymen as well.

Robert
 

Offline Spawn

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Re: Extech MM570A video review and teardown photo's
« Reply #27 on: January 24, 2013, 02:17:57 am »
I have an Amp Probe AM140 and the inside looks very similar. This leads me to believe that it is also a Brymen as well.

Robert

Yes, It has been discussed before, the meters there are older models, like the Extech there is MM570 and mine is MM570A, I would love to see the difference in those two to be honest.
And there is also GreenLee with same guts too, so in total 4 brands are using same multimeter in their own colors.

See here
« Last Edit: January 24, 2013, 02:28:39 am by Spawn »
 

Offline nanofrog

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Re: Brymen 857A for comparison purposes
« Reply #28 on: January 24, 2013, 02:32:34 am »
Thanks for sharing the pictures with us.

Having just fixed a 25+ year old Fluke 8060A due to 5 out of 10 electrolytic capacitors leaking its electrolyte, I hope those two electrolytic caps don't leak on you anytime soon.  In Spawn's pictures, it looks like they have been replaced or removed.
Glad I had something worth posting for a change (not the same exact thing others have done).  ;)

Good catch on the electrolytics. No sign of leakage yet, and hopefully they won't any time soon. But I'll certainly have to keep an eye on them when I check the battery.

Thanks a lot for the teardown! It does indeed look quite different from the latest Brymen models. Still seems like super good value for money for the price you paid though!
At what I paid, definitely.  ;D

I'm not so sure at full price though, depending on location. Not so much in the US for example, as by the time better leads and a data kit are added, the price comes in around what an Agilent U1252B goes for (BM869/Greenlee DM-560A + leads + data kit vs. U1252B when it includes the BT adapter for free, which they seem to do fairly regularly it seems).

I can see what we talk about nanofrog, it is actually weird they keep same housing and try to improve over the years, mostly these kind manufacturers change the shape of the meter over the years, 10 years difference taught them something and they improved on the newer models it seems, I see some things un unpopulated on your main PCB which are filled on mine like the ones under the shield on my PCB.  It is like Fluke 80 series improving over the years but changes are not much as this one.

You got yourself hell of a meter for that price, it is just great  :-+
Likely cheaper and faster to concentrate on the PCB alone, as they don't have to create new injection molds.

As per the cost, definitely for what I paid.  :)

I have an Amp Probe AM140 and the inside looks very similar. This leads me to believe that it is also a Brymen as well.
Can't recall the innards of the AM140, but as Brymen appears to be primarily an ODM, and how similar the features (and identical soft key layout is), it's likely IMHO.

Yes, It has been discussed before, the meters there are older models, like the Extech there is MM570 and mine is MM570A, I would love to see the difference in those two to be honest.
And there is also GreenLee with same guts too, so in total 4 brands are using same multimeter in their own colors.

See here
Which Greenlee?

The DM-560A is the newer model (same as the BM869A), not the older BM859CFa (big brother of the BM857A I have).
« Last Edit: January 24, 2013, 02:34:28 am by nanofrog »
 


Offline nanofrog

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Re: Extech MM570A video review and teardown photo's
« Reply #30 on: January 24, 2013, 03:23:18 am »
This one here nanofrog, and cost a lot more than any of these I bleave:

.... Greenlee DM-860A....
If you would, please tear it down, and post pics. Would be seriously interesting to compare it to the BM857A (might give me a few ideas...  >:D).  :)
 

Offline Spawn

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Re: Extech MM570A video review and teardown photo's
« Reply #31 on: January 24, 2013, 03:30:04 am »
I don't have one, and when I see the price I will never get one either  :-DD

Offline nanofrog

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Re: Extech MM570A video review and teardown photo's
« Reply #32 on: January 24, 2013, 03:34:25 am »
I don't have one, and when I see the price I will never get one either  :-DD
Ah, OK.

Thought you might have one (pic of your meters might not have been as obvious if it was "naked").  ;)

I'd love to see detailed images of the PCB's on one of those though...  >:D
 

Offline Lightages

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Re: Extech MM570A video review and teardown photo's
« Reply #33 on: January 24, 2013, 03:38:48 am »
It is almost a sure thing that the Greenlee is exactly the same meter as the Brymen.
 

Offline nanofrog

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Re: Extech MM570A video review and teardown photo's
« Reply #34 on: January 24, 2013, 03:53:58 am »
 :-*
It is almost a sure thing that the Greenlee is exactly the same meter as the Brymen.
I expect so.  :)

But I'd love to see pics of the PCB's to get a better idea of what they changed between the two models (what parts are/aren't populated besides the fuses).  ;)
 

Offline rbola35618

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Re: Extech MM570A video review and teardown photo's
« Reply #35 on: January 24, 2013, 04:04:42 am »
Spawn,

Great review and photos were also very helpful. Job well done!!

Robert
 

Offline Spawn

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Re: Extech MM570A video review and teardown photo's
« Reply #36 on: January 24, 2013, 08:41:12 am »
Spawn,

Great review and photos were also very helpful. Job well done!!

Robert

Thanks for the nice feedback :)

Thought you might have one (pic of your meters might not have been as obvious if it was "naked").  ;)

Yeah, I should line them up and make a new family photo, I just look at it and Fluke 87 was missing on the photo.

Offline nanofrog

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Re: Extech MM570A video review and teardown photo's
« Reply #37 on: January 24, 2013, 11:45:20 am »
Yeah, I should line them up and make a new family photo, I just look at it and Fluke 87 was missing on the photo.
Sounds great, but please put some "clothes" on them. Might make it easier to ID.  ;)
 

Offline Spawn

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Re: Extech MM570A video review and teardown photo's
« Reply #38 on: January 24, 2013, 06:57:59 pm »
Might make it easier to ID.  ;)

I know this is going to sound weird, but even I have couple meters from same model, I still know which one is which, no markers or what so ever.

Offline rsjsouza

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Re: Extech MM570A video review and teardown photo's
« Reply #39 on: February 17, 2013, 05:57:07 am »
nanofrog, I snatched the last Brymen of that eBay seller and, although the probes were not in a bag, the DMM looked brand new (no marks or spots at all). I also see that, just like mine, yours is a BM857 and not a BM857a - Brymen's picture shows a different marking. I am not exactly sure what is the difference other than using a different data cable. From the Extech video I see that the continuity is latched (mine is not).
Despite this, this is an incredible and fully featured DMM. In my opinion the smart details are the highlights: the cable detection (I already blew two 440mA fuses of my Fluke 179), the NVRAM that stores the last option used with a power off, the manual that explains some technical terms and is actually written in good english, and a very speedy bargraph.
The lowlights are the backlight and the flimsy stand...
All in all, I am very happy with it.
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Offline nanofrog

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Re: Extech MM570A video review and teardown photo's
« Reply #40 on: February 17, 2013, 03:58:40 pm »
nanofrog, I snatched the last Brymen of that eBay seller and, although the probes were not in a bag, the DMM looked brand new (no marks or spots at all). I also see that, just like mine, yours is a BM857 and not a BM857a - Brymen's picture shows a different marking. I am not exactly sure what is the difference other than using a different data cable. From the Extech video I see that the continuity is latched (mine is not).
Despite this, this is an incredible and fully featured DMM. In my opinion the smart details are the highlights: the cable detection (I already blew two 440mA fuses of my Fluke 179), the NVRAM that stores the last option used with a power off, the manual that explains some technical terms and is actually written in good english, and a very speedy bargraph.
The lowlights are the backlight and the flimsy stand...
All in all, I am very happy with it.
No "a" printed on the meter or box in the model number for my unit either, but the data sheet on their site does.  According to the seller, these came from a liquidated company, and must have sat on a shelf for a very long time, as the date codes in mine put manufacture in 2000 (perhaps these originally didn't have the battery installed and prevented corrosion on the connector terminals). Had the included manual been an issue, the one for the Extech MM560A can be substituted if it were needed (or used to look over prior to purchase).

NOS or not, no big deal IMHO overall. It does have some issues (fuses rated at 500V, continuity is scratchy with the included probes would be others), as most meters, but at $70 - 100 (depending on which seller), it's a good deal. For those outside of the US, it could be a different story, depending on what's available to them.

BTW, that seller has more from what I understand (from an email), so there will be more listings in time for those interested (keep an eye out).
 

Offline rsjsouza

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Re: Extech MM570A video review and teardown photo's
« Reply #41 on: February 17, 2013, 11:43:08 pm »
According to the seller, these came from a liquidated company, and must have sat on a shelf for a very long time, as the date codes in mine put manufacture in 2000
This and the 500V fuses make me believe ours may be a previous revision, especially when compared to the MM560A internals. I am so happy with the price/features ratio that I really don't mind at all. I would never pay the $428 Amazon is charging for the Greenlee.

It does have some issues (fuses rated at 500V, continuity is scratchy with the included probes would be others), as most meters, but at $70 - 100 (depending on which seller), it's a good deal.
Yes, I don't like the scratchy continuity, but at least is ridiculously responsive. Regarding the 500V fuses, I personally don't care as long as I know it beforehand - both the manual and the website make that perfectly clear, which is very nice.
 
One thing I couldn't find is the burden voltage. Could you find this info anywhere?

BTW, that seller has more from what I understand (from an email), so there will be more listings in time for those interested (keep an eye out).
That is very nice to know. I'll be on the lookout.
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline nanofrog

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Re: Extech MM570A video review and teardown photo's
« Reply #42 on: February 18, 2013, 02:33:01 am »
This and the 500V fuses make me believe ours may be a previous revision, especially when compared to the MM560A internals. I am so happy with the price/features ratio that I really don't mind at all. I would never pay the $428 Amazon is charging for the Greenlee.
Nor me.

Yes, I don't like the scratchy continuity, but at least is ridiculously responsive. Regarding the 500V fuses, I personally don't care as long as I know it beforehand - both the manual and the website make that perfectly clear, which is very nice.
Completely went away for me by using better probes (horrible with the included probes, got better with the Agilent probes, and vanished with a couple of different Probemaster sets I have on hand).

BTW, if you look closely at the PCB, it's designed to accept the larger fuses and legend states the current values (both 600V). Easy upgrade for those interested.
 
One thing I couldn't find is the burden voltage. Could you find this info anywhere?
Page 18 in the manual that came in the box (values listed for DC Current, AC Current, AC + DC Current).

If you're missing this in your manual, let me know, and I'll post it for you.
 

Offline videobruce

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Re: Extech MM570A video review and teardown photo's
« Reply #43 on: February 18, 2013, 02:08:47 pm »
To the OP, great job on the review.  :-+
 

Offline Spawn

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Re: Extech MM570A video review and teardown photo's
« Reply #44 on: February 18, 2013, 04:12:07 pm »
Thank you  :) I am glad you like it, waiting for more equipment so I can do more reviews.

Offline rsjsouza

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Re: Extech MM570A video review and teardown photo's
« Reply #45 on: February 20, 2013, 12:58:35 pm »
Completely went away for me by using better probes (horrible with the included probes, got better with the Agilent probes, and vanished with a couple of different Probemaster sets I have on hand).
I can confirm it was almost vanished with my TL75 probes as well.

BTW, if you look closely at the PCB, it's designed to accept the larger fuses and legend states the current values (both 600V). Easy upgrade for those interested.
Yes, mine has that as well.

One interesting thing is that I did some testing on several open fuses (1AG, 3AG, 5AG) with my neon transformer and found the 3AG (glass) broke up at around 6.4kV (rms). If the glass was coated from the inside with the destruction of the element, it broke down at around 4.8kV. The 5AG only broke at around 10.8kV. Unfortunately I didn't have any 3AB (ceramic) to test. The 1AG gave up at around 2.4kV. Obviously that these don't supersede the manufacturer specifications, but it surely shows that lower rated fuses can proably still pass CAT rating tests.
 
Page 18 in the manual that came in the box (values listed for DC Current, AC Current, AC + DC Current).
Duh! Thank you! This is one of these things that are so obvious you don't notice.
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline Lightages

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Re: Extech MM570A video review and teardown photo's
« Reply #46 on: February 20, 2013, 02:48:51 pm »
One interesting thing is that I did some testing on several open fuses (1AG, 3AG, 5AG) with my neon transformer and found the 3AG (glass) broke up at around 6.4kV (rms). If the glass was coated from the inside with the destruction of the element, it broke down at around 4.8kV. The 5AG only broke at around 10.8kV. Unfortunately I didn't have any 3AB (ceramic) to test. The 1AG gave up at around 2.4kV. Obviously that these don't supersede the manufacturer specifications, but it surely shows that lower rated fuses can proably still pass CAT rating tests.

I would not jump to that conclusion. A neon transformer is not going to be able to provide the current to start a nice plasma of any power. The test voltages and currents used in CAT rating tests are far beyond what you can hope to supply with that transformer. If you could provide pulse from a 2 ohm source at 8kV+ then you might have a real test. If you do have something to do this, I hope we hear from you again......
 

Offline SeanB

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Re: Extech MM570A video review and teardown photo's
« Reply #47 on: February 20, 2013, 04:10:04 pm »
I have done that test and the ceramic fuses do survive, though the glass ones turn into powder and metal vapour. testing a microwave which did intermittent fuse blowing, so got a box of 10 glass fuses and sleeved them with glass sleeving to contain the blast ( a box cost the same price as the one 10A ceramic, so a box it was) somewhat so the pieces would not bew all over the inside. Found the faulty interlock bar, and adjusted it to stop blowing fuses then put the ceramic one in. Glass sleeve did need changing every 3 fuses or so as it was full of glass shards.

Funny thing is the high voltage fuses are nothing more than a 1A glass fuse inside a plastic casing with a lead on the ends. Nothing fancy, and often for testing I replace the blown fuse with a jumper wire to see what is faulty - magnetron ( not often it goes short, mostly low emission), diode ( more likely than magnetron but not common) or capacitor ( common). That is about all other than a faulty transformer on the HT side, most HT fuses blow due to dirt building up on the capacitor or diode terminals or a faulty fan. LT fuse can be anything........ Commonly switches.
 

Offline rsjsouza

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Re: Extech MM570A video review and teardown photo's
« Reply #48 on: February 20, 2013, 10:54:54 pm »
I would not jump to that conclusion. A neon transformer is not going to be able to provide the current to start a nice plasma of any power. The test voltages and currents used in CAT rating tests are far beyond what you can hope to supply with that transformer. If you could provide pulse from a 2 ohm source at 8kV+ then you might have a real test. If you do have something to do this, I hope we hear from you again......
I agree with you that the CAT ratings measure other aspects with fully working DMMs with good fuses (thus the need for the power supply you mentioned), and my comment was more toward a suspicion that a manufacture could have a slim chance to pass some of the tests with a 3AB/3AG fuse, given the air gap would only ionize at several kV. I should have specified better in my comment below.

All that said, my test was intended to check the maximum voltage of the gap between the fuse electrodes (as it was open) and not cause the rupture of its element (or its mechanical assembly). For that any high voltage source is enough. As SeanB mentioned below, even with that I was able to shatter glass fuses with a mere 30mA.

Anyways, I don't want to hijack the thread with my fuse experiments... Sorry.
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline Wytnucls

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Re: Extech MM570A video review and teardown photo's
« Reply #49 on: February 20, 2013, 11:26:40 pm »
The latest IEC 61010-1 (Safety requirements for electrical equipment for measurement, control and laboratory use) require fast blow HRC fuses with a voltage rating at least equal to the CAT rating of the multimeter.
Glass fuses won't do anymore. I notice CEM in China is now installing 1000V HRC fuses in their new DMMs.
Also, the DMM testing on the amp side is done with ruptured fuses, with a constant 2000V applied to the input jacks for 2 minutes, if my memory serves me right. The purpose is to check for destructive arcing between fuse, fuse holders, jacks and PCB traces.
The other inputs are tested with higher pulsed voltages.

http://www.cem-instruments.com/en/pro/pro-466.html
« Last Edit: February 20, 2013, 11:43:57 pm by Wytnucls »
 


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