Extech EX470 Multimeter teardown - Page 1
Forum section: electronics / testgear

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 14, 2013, 01:17:26 am
content: Before I get into my own review I would like to give a nod to some members (Medo, patb) who provided pictures of their EX430s. I suspect some of what they found would apply to this review.https://www.eevblog.com/forum/testgear/extech-ex430-multimeter-teardown-photos/https://www.eevblog.com/forum/chat/extech-430/msg55853/#msg55853I’ve seen there are a few Extech teardowns on the EEVblog but I’m contributing another. I kind of regret to say I’m not overly impressed with this meter and it didn’t get better when I got inside the thing. The EX470 is true RMS meter with both IR and K-type thermocouple temperature readings. I only did a limited test of accuracy, a physical look over and then the tear down.So starting from the outside things aren’t bad. The meter feels good in the hands and only creaks just a small amount when twisted. That might not be fair since one of the case screws is stripped. The protective boot fits well but feels thin. I don’t feel like it would offer as much shock protection as the boots on the Flukes or even the Ideal meter I tore down. I like the tilting stand design. It has detents every 45 degrees from flat down to flat up for hanging. The detents feel strong so I wouldn’t worry about staying in position. Nice touch there. Following some Dave tests, you can’t turn the selector or really press buttons when the meter is in some stand positions because it doesn’t have the weight/friction to stay in place.The control knob feels and sounds rather cheap in my book. It’s also rather shallow and not the easiest thing to grab. I think the problem is the height of the part you can grab tappers down at the ends. You are really spinning it by the center and that makes it feel cheaper and stiffer. Certainly not the end of the world but I think the design was corrected with the later Extechs.The input jacks don’t feel very secure but the current jacks do have an audible warning and small on screen icon if you aren’t in current range. I wish it was more aggressive but thumbs up for any such warning!Taking readings:Well I didn’t take many, just a few quick comparisons with my Fluke 87 V and Agilent U1241. The readings I took seemed within spec, assuming the other two are “true”. I don’t care for the tall font on the screen. It’s not that easy to read and that forced all the other things like unit markings to be quite small. Many others seem to have this right but this model doesn’t. The backlight, green LEDs , lights the display but is patchy and adds a, well depth, to the display when on. That makes the legibility lower than on some other meters. Again, nothing that keeps stuff from working in low light but it doesn’t say quality either.The only measurement range that I had a concern about was the K-type temp range. I was getting readings that were 4 F (~2 C) higher than I got using the same thermocouple with my Fluke and Agilent meters. The IR readings seemed to match the thermocouple as well. It also seemed to take longer for the K-type temps to stabilize vs the other meters. The IR readings seemed good as compared to my other IR thermometer and I liked the included laser. Interestingly, if you punched “Relative” in F range then switched to C, the value of F was still used as your relative. So if you had a 70 degree wall and hit relative the temp would show 0. When you switched to C and now the meter sees a ~21 C wall it would show a -49C temperature! It would probably be best if the relative values didn’t retain across ranges.The auto ranging on the resistance could be faster. The continuity tester is both slow AND scratchy. The probes seem to have a bit higher surface resistance than some others I’ve used. They don’t feel cheap but also not Fluke like.I did notice that a battery that read 8.2V and didn’t throw a low battery warning in one of my meters did so in this one. Also with low batteries the IR readings can be off.So on to the back.The battery is held with screws into metal inserts, nothing bad about that. The case screws are self-tapping. Who ever got in this one last messed up one of the bosses. The others went back together nicely so I suspect it would take a careless hand to mess one up. I say whoever was last because I generally am very careful about stripping these things and have a good touch. Also because it might explain the glass fuse I will talk about later.And inside.Thanks to Dave the first thing I notice is fuse types. This meter has a ceramic on the 20 A range (250V) but a small glass fuse on the lower range. I think that is actually a replacement because some of the EX430 photos on this forum show ceramic fuses in both locations. That would also explain the stripped threads on one case screw.The next thing I notice is the total lack of blast shielding. I guess there is some physical separation but really the high voltage lines are run all over the meter. For example the voltage input runs from the jack to the vertical header half way up the meter and then all the way back down the main board to next to the jack where the PTC is located. The input protection seems very minimal by the standards of a meter that should cost $100.

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 14, 2013, 01:30:07 am
content: More pics

author: Lightages
author_rank: Unknown
timestamp: July 14, 2013, 03:44:27 am
content: From your wording, it seems you got this used?

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 14, 2013, 04:24:19 am
content: Quote from: Lightages on July 14, 2013, 03:44:27 amYes. That is why I'm not willing to assume the glass fuse is not original. The accuracy seems off a bit. Since it's used that could be the issue though it does seem like Extech meters are a bit hit and miss.Edit: "NOT original"

author: Lightages
author_rank: Unknown
timestamp: July 14, 2013, 04:28:21 am
content: Yes, the EX series seems to be very poor. The MM series made by Brymen are much better I think.

author: retiredcaps
author_rank: Super Contributor
timestamp: July 14, 2013, 06:13:56 am
content: Thanks for another review and teardown.I had an EX430 and most of your findings mirror my feelings.

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 14, 2013, 12:25:44 pm
content: Someone had posted the ODM for these meters but I can't find them now. It was a 3 letter name. Any idea?

author: Wytnucls
author_rank: Super Contributor
timestamp: July 14, 2013, 02:00:46 pm
content: One of the smaller Chinese manufacturers: C.E.M, but I'm not sure they made this particular one.

author: metalphreak
author_rank: Frequent Contributor
timestamp: July 14, 2013, 03:28:11 pm
content: I've mentioned C.E.M being the ODM for the EX520 before. This one says TOPMAN INDUSTRIES on the PCB which I haven't seen on the CEM meters.

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 14, 2013, 03:42:11 pm
content: Given the big difference in how the 470 vs 520 is made I can believe that.

author: Wytnucls
author_rank: Super Contributor
timestamp: July 14, 2013, 03:53:47 pm
content: Topman Industrial is a Hong Kong based PCB manufacturer.

author: Robomeds
author_rank: Frequent Contributor
timestamp: July 14, 2013, 08:02:59 pm
content: So do we think this is a Topman design or just a Topman PCB in someone else's design?