EEVblog #94 - Page 1
Forum section: electronics / general

author: orbiter
author_rank: Frequent Contributor
timestamp: June 14, 2010, 10:29:43 pm
content: Dave. Calm down mate, your gunna blow a fuse of your own if you carry on like that. I for one don't want to see blog #95 titled... Daves head blows offOrb

author: Ferroto
author_rank: Frequent Contributor
timestamp: June 14, 2010, 10:39:09 pm
content: I'm sure he's saving that for number 100

author: Ferroto
author_rank: Frequent Contributor
timestamp: June 14, 2010, 10:40:01 pm
content: Quote from: Ferroto on June 14, 2010, 10:39:09 pm<---- Speaking of which this is my 100'th post

author: MrPlacid
author_rank: Frequent Contributor
timestamp: June 15, 2010, 12:35:06 am
content: Quote from: orbiter on June 14, 2010, 10:29:43 pmNo, don't calm down Dave. The louder you are the faster Extech will respond.<---10.0th post:)

author: EEVblog
author_rank: Unknown
timestamp: June 15, 2010, 12:44:50 am
content: Quote from: MrPlacid on June 15, 2010, 12:35:06 amExactly. This is a big safety issue and Extech need to fix it. You can't sweep these things under the carpet.They have been very responsive previously, let's see what happens this time...Dave.

author: charliex
author_rank: Frequent Contributor
timestamp: June 15, 2010, 01:17:52 am
content: This should be good,/goes off to watch!

author: PetrosA
author_rank: Frequent Contributor
timestamp: June 15, 2010, 03:03:37 am
content: There's a common practice in N. America for designing grounding (earthing) prongs called "first make, last break" which basically means that the ground (earth) prong, being responsible for preventing shock hazards, must be the first to make contact and the last to break contact when plugging in or unplugging any kind of device. The same concept should apply to any safety switch in a tester like this. If that switch is what was responsible for creating the hazard condition, the designers obviously never heard of this concept and completely didn't do their job correctly and I'm very surprised that the tester would actually get a CAT III rating. Dave's idea to have it default to high voltage mode would be a much better solution. Kudos to ya, mate!

author: orbiter
author_rank: Frequent Contributor
timestamp: June 15, 2010, 10:05:58 am
content: QuoteQuoteSorry. I meant the first post to be light hearted, should have put j/k at the endI quite understand the safety issue here and I agree.. Dave does a great job in bringing them to the fore. But I tell ya if blog #95 does turn out to be.. 'Daves head blows off.' What are we guuna do then when equipment comes up short (no pun intended.) We can't just go out & buy another DaveOh nearly forget again.. J/k heheeAs I always say.. Keep doing what your doing Dave.Orb

author: MyZirconia
author_rank: Contributor
timestamp: June 15, 2010, 04:37:28 pm
content: Finally we saw the real Dave in the end there when he stamped on the meter.(just kidding)That whas truly a idiot design just to rely on a pushbutton and a internal bad functioning switch.are you going to send the meter to Extech with the footprints on it?The only good thing is that you still alive and hopefully they redesign the meter..just state in the manual that you should switch it to voltage is really dangerousmany people (and Dave) do not read the manual until there is a problem ora function issue.waiting for the response from Extech/magnus

author: TheWelly888
author_rank: Frequent Contributor
timestamp: June 15, 2010, 06:59:25 pm
content: I can't believe such a dangerously flawed design is on the market!!!My God! Only one switch spacing away from blowing up an IC with 240V!! And how on earth was that a CAT III multimeter, not exactly a $10 jobbie either!You should have executed that thing with Doug Ford's "Blow-Shit-Up" machine rather than stamped on it ( blindfold the display first )

author: MyZirconia
author_rank: Contributor
timestamp: June 15, 2010, 07:23:24 pm
content: Here David i found the perfect thing for you to do with bad productshttp://www.blendtec.com/willitblend/Get one of these to run your thumbs down item in/Magnus

author: TheWelly888
author_rank: Frequent Contributor
timestamp: June 15, 2010, 07:46:24 pm
content: I've just taken a look at the IC datasheet again and I noticed that date of it was 15th April 2010 ( or at least that's how I interpret 10/4/15 on each page ) If that IC was so new to the market then Extech must have been too hasty in putting the meter out?

author: Ferroto
author_rank: Frequent Contributor
timestamp: June 16, 2010, 11:43:33 am
content: Quote from: MyZirconia on June 15, 2010, 07:23:24 pmI'd rather see bad products get blown up with that massive PSU that you used to blow up those multimeters.

author: saturation
author_rank: Super Contributor
timestamp: June 16, 2010, 07:11:32 pm
content: This an example of when using questionable meters to worry if they are good for mains voltage or not, which is just CAT II. Although one can expect more from Extech, there are safer meters on the market with decade long reputation. Why settle for less?The blow up and flash portion focused near the rubber orange switch, and while shrapnel won't be lethal, it could cause problems with your hand if shards need to be removed.Also, the input protection was completely bypassed, so it was useless for protecting this fault, the chip itself seems to have blown.Given these, a tweezer adapter for use on any DMM is a better option than worrying about DMM LCR tweezer devices.Quote from: EEVblog on June 15, 2010, 12:44:50 am

author: Unknown
author_rank: Unknown
timestamp: June 16, 2010, 09:14:06 pm
content: Quote from: saturation on June 16, 2010, 07:11:32 pmEven worse, this was probably just a regular 230/240V input, not even the 2kV or so transient specified by CAT II 600V (let alone CAT III).Quote from: saturation on June 16, 2010, 07:11:32 pmJust a note, I believe this was a tweezer type DMM, not LCR meter. I don't typically connect LCR meters to mains, so input protection for LCR meters is less of an issue in my opinion (although it should meet its specified CAT ratings).

author: EEVblog
author_rank: Unknown
timestamp: June 16, 2010, 10:13:07 pm
content: Quote from: alm on June 16, 2010, 09:14:06 pmCorrect. This meter is designed and manufactured as a proper DMM to measure mains voltages. It was supposed to be completely safe, but a design goof-up.Just got an email that Extech have easily reproduced the fault, more to follow...Dave.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 16, 2010, 11:37:07 pm
content: I have one of these, but a different colour and branded Tenma. Can't remember if it actually came with the probes. On the battery compartment there is a label that says "Danger Measure Over 35V" - I'm guessing this may just mean don't poke a finger in the bat compartment when live...!I think the root (Sorry I know this word has other meanings Down Under!) problem here is unnecessary specmanship in providing a high voltage capability at all.There is no reason that a simple product like this, which is primarily aimed at component testing, should even be specced to be able to measure mains voltages. By all means provide 4mm sockes so you can use probes or a jig, but mark it clearly as only suitable for low voltages. It isn't a general purpose DMM and nobody is going to buy it as one.I really don't think many potential purchasers of a device like this would decide not to buy because it didn't have a high voltage range...and I don't believe that switch (which is just a sliding contact over PCB pads) has sufficient creepage/clearance to be used as a safety isolation component either.

author: saturation
author_rank: Super Contributor
timestamp: June 17, 2010, 12:05:36 am
content: This is great, Dave, not only was the show entertaining, you found something they missed in testing, and will likely benefit them from dealing with returns on damaged goods, or worse safety litigation, so I hope you get more than a new meter to play with!Alm, my bad, I didn't meaning plugging an LCR meter into the mains, but another Extech clone, the Tenma as mike mentions. I agree fully with Mike's analysis. If I were to buy such a thing, it would be a cheap alternative to the more ergonomic Canadian tweezer, so making it also DMM capable and having to deal with mains protection, and when there are far better DMMs to do such a thing well, just made a potentially good device, bad.There is a pure LCR Extech device what is smaller and more in the Smart Tweezer range, and no allusion that it can be plugged into mains or work as a DMM:Quote from: EEVblog on June 16, 2010, 10:13:07 pm

author: EEVblog
author_rank: Unknown
timestamp: June 17, 2010, 12:55:54 am
content: Extech have offered the RC100 RC meter for review but I turned them down. I already have another two Extech products to review (3 if you count the LCD microscope that's supposed to be on it's way), I didn't want the blog to become the "Extech Show".Dave.

author: EEVblog
author_rank: Unknown
timestamp: June 17, 2010, 01:05:59 am
content: Quote from: mikeselectricstuff on June 16, 2010, 11:37:07 pmSome people have missed the point here I think. The meter was supposedly designed and tested to be CATIII 600V rated. It was simply the bad design of the interlock switch that causes it to fail under certain circumstances.So there is nothing inherently wrong with the concept of having a RC/Tweezer type meter with interchangeable high voltage probes.Yes, the unit has that sticker you refer too, and I too assume it only applies to the battery compartment.When the unit is sealed and the high voltage probes attached properly the unit is supposed to be completely safe for use on high voltages.Dave.

author: StephenOng
author_rank: Newbie
timestamp: June 17, 2010, 01:51:02 am
content: I looked up the tenma probe. (http://www.mcmelectronics.com/product/TENMA-72-8485-/72-8485) Externally it looks identical to the extech model. The Tenma model do not claim any kind of CAT rating.

author: Polossatik
author_rank: Frequent Contributor
timestamp: June 17, 2010, 01:31:22 pm
content: Quote from: EEVblog on June 17, 2010, 12:55:54 amExtech LCD microscope? Going to check for viruses in chips?They can't be seriously asking $299.99 for that stuff???320x240 pixels rofl...com'on for that price you have a decent compact with macro setting.... Or an older DSLR.. I got a Nikon D70 for 150 euro (with lens)...

author: Ferroto
author_rank: Frequent Contributor
timestamp: June 17, 2010, 05:36:34 pm
content: Quote from: polossatik on June 17, 2010, 01:31:22 pmSometimes I have trouble seeing some of the numbers on IC's and SMD components, I just use a $10 pair of reading glasses.

author: EEVblog
author_rank: Unknown
timestamp: June 18, 2010, 01:03:22 am
content: Quote from: polossatik on June 17, 2010, 01:31:22 pmAs always, it's horses for courses.Does the Nikon have 7-27 times optical zoom and live display for inspecting parts and joints?Is the Nikon small enough to just sit on the bench and be used one hand inspecting a board for long periods?Does the Nikon have a continuous illumination light?Can the Nikon give you live imaging on a PC screen?etcThe Extech is not a digital camera, and the Nikon and other digital cameras are not hand held inspection microscopes.Whether or not it's actually useful I will reserve judgment until I actually play with it.Dave.

author: PetrosA
author_rank: Frequent Contributor
timestamp: June 18, 2010, 01:08:39 am
content: Quote from: EEVblog on June 18, 2010, 01:03:22 amI have to admit that when I was a few months away from turning 40, I noticed a fast degradation of my eyesight. I haven't had time for a few years to make any models (the scale kind...) but I'm a little nervous about it now and something like this camera might be needed sooner than I think.

author: slburris
author_rank: Frequent Contributor
timestamp: June 18, 2010, 08:56:43 pm
content: I use this digital USB microscope:http://www.dino-lite.com/Microscope-Products-More.aspx?product_number=AM311S-Dino-LiteVery handy for inspecting for solder bridges on 100 pin VQPF packages! Of course I also usea head mounted magnifier, but this gives me a second view on things I'm not sure about.Scott