EEVblog #94 - Near Death Multimeter Experience

hi welcome to the EEV blog and electronics engineering video blog of interest to anyone involved in electronics design I'm your host Dave Jones hi now I was going to do an equipment review of this cute little X tech RC 200 tweezer type multimeter check it out isn't a quite neat I thought it was really cool little gadget and how the tweezers disconnect like that and you get these standard probes which plug in like that and it's cat 3 input rated fantastic I thought I liked how it's got Auto scanning modes it's got a net capacitance range the continuity tester worked really well I was going to rave on about how it's got a nicely designed little battery holder on the back and it comes with a soft case it was really quite enjoying this little um quite unusual multimeter and I was looking forward to doing a review of it this afternoon but I can't why cuz the piece of blew up in my hand oh that's right the damn thing blew up in my hand when I was trying to measure 240 volt mains I was holding that like this probe in the 240 volts as I do bang the damn thing before it didn't literally blow apart but it was one hell of a bang and I would jump 10 feet across the room dancing near killed me so clearly there goes the review because all I've got is a charred meter I don't have another one to do a review not that I would anyway because this thing has a serious safety issue which needs to be addressed I think I know possibly why it blew up so let's take a look at it now I actually felt quite safe probing the mains with this thing because well it's an X Tech for a start right it's a big brand name the probes are our cat for actually input rated it's a cat 3 input rated meter to 600 volts and take a look at the brochure for it here's a photo from the brochure where you can see somebody probing the mains with it no problems at all so you think this meter is perfectly capable of probing the mains and I'm sure it is if it's used correctly but if you use it in correctly and I think there might be a design there's either a way to use it incorrectly or a design quirk in it that will make it blow up if you measure high voltages it's crazy now unfortunately I don't have another one of these meters to do further tests and it's a bit charred inside which makes it a bit hard to trace out and things like that exactly what's happening so I'm going to have to rely on ex tech to do investigations and find out exactly what the cause is but I think it's one of two possible reasons number one is that if it can't handle our 240 volts or you know high voltages on the on the resistance the capacitance or the diode or continuity range then well that's just rooted really that means that the product should leave me on the market if it can't do that especially one that shows people probe in the 240 volts mains and especially one that only has a single mode switch like that because you know it's understandable if you've got a big rain switch like that you turned around the current mode or something like that and short out the mains well you know you're just an idiot for you know switching in the current mode or something but this thing should be able to handle 240 volts on all of the ranges considering it has no current ranges at all and if it can't do that it's screwed so I'm not sure if that was the problem because in the manual it does actually state that you should switch it to 240 and they should switch it to our voltage measurement mode before you do the actual measurements and well I didn't do that I had it on auto scan mode and pay you know silly me dirt right Auto scan mode you would think would be able to handle you know voltages on there because if you accidentally press that mode button you don't want to think blowing up in your hand that's ridiculous expect a lot better from a professional meter and grant it I didn't read the manual beforehand and here it is I'll put it up this is what it says on the first page are number 5 down here a tiny little number 5 never connect the meter leads across a voltage source while the function switch is in the capacitance resistance or diode mode doing so can damage the meter okay fair enough I didn't read the manual you think right well if this thing can't handle 240 volts on the ohms range then it's a piece of and it shouldn't be on the market really especially when you can simply accidentally press the mode switch and put it into Auto scan diode capacitance do capacitance resistance mode something like that if you're if even if you've got it set to the correct voltage mode like it says in the manual and you put it in voltage mode and you plug in the probes and you stick it into the 240 volt mains if you accidentally press that button it'll blow up on you and well that's one of the modes I don't know if that's the mode for sure but if it does that then that's a serious design issue and it's screwed right there now if it's not that issue I reckon it's this one plugging the probes into the unit like this okay I plugged mine in like that you see the gap there right it requires a lot of force I'm putting a lot of force in there to to force that together completely okay and it takes a lot of force to take it apart so when I think when I was doing my maze measurement it wasn't plugged all the way in like that it was you know it was plugged sort of most of the way until you know it was a good solid connection like that but let's take a look inside and see if there's a problem there I think there is now this is actually quite a nice design aspect there's a little switch here see this black thing here okay it's actually got a little lever on it like that which is you probably can't see it but it's down in there so when you actually plug in these um tweezer probes okay they only go in one way because they're keyed like that and there's a little curve thing over there it's a really nice really nice design okay you plug that in and that switch does not move at all okay now if you get the probes like this okay you plug the probes in I think it goes in that way yes it does okay plus and plus look there it is right plus and plus it's a really nice actual designer once again it's actually got a curved thing in there which matches up to there it's a keyed based thing but what watch this right when you plug it in okay now that's where I plugged it in when I think I did the test okay and that switch didn't move but if we plug it in all the way see let's switch that that plunger just came out and move that switch now I think that's what the issue is it's a really nice design aspect and that switches the meter I think into into voltage mode and it's supposed to be fully protected and it should handle 240 volts but because I only plugged it in part of the way like that and the contacts engaged inside before the switch turned over like that so they've actually got that design completely and utterly back to front it should be so that when you plug in these tweezers it pushes that switch out and when you plug in these it defaults to the fully protected voltage mode but I don't think it does so I think that's what the issue there I'm not 100% sure I'm still relying on X Tech to do some evaluation and actually tell me that but I think there's a serious design flaw that's back to front that makes this meter dangerous to use what a piece of okay now if you're actually curious to see what damage was actually done there's a there's a capacitor down there which is blown there's a few passive components around here which are which have Loen and nothing else on the top they've got a PTC there and they've got a couple of mobs as well add that they didn't actually blow but this input resistor here is a bit char there's some charring on there the real issue is if you flip it over like this bingo look at the soft rubber switch look at all the cherry on that rubber switch they're unbelievable and the bottom side of the of the rubber switch contacts it's all char completely around there so imagine if you had that thing plugged in and you had your fingers on those buttons God could it you know the explosion could escape out through the buttons and it's crazy and also the the chip has a really nice hole blown in it there now the backup that theory here's a data sheet for the Cirrus tech ES 51 nine to eight chip which is used in this actual meter okay here's their example circuit this is not the circuit which is in the extech RC 200 okay this is just the example circuit from Cirrus tech but I believe it's going to be very similar now you can see switch seven there the RC D continuity switch and that one is the one I believe is that is that keyed engagement switch when you plug the probes in when you plug the voltage probes in it disconnects that switch and sends the voltage from the input through to through the 10 Meg resistor into the VR one input of the chip and it should handle that and it should be fully protected and there's an overload there's the inputs arm PTC and moth protection devices there as well which aren't shown on here but that's what should actually are protect the meter but what happened is because we plugged in the probes and that switch didn't engage the 240 volts we were measuring went through that variable pot there and went through the PTC onboard a couple of those passive parts and those passive parts are the ones that you see blowing up on the top side of the board so I think that's pretty good confirmation that that's what the actual problem was so there you go that's not entirely conclusive but I reckon that's what the problem was I just didn't plug these probes all the way in and there's nothing in the manual to tell you that you should actually do that and even if you do and they put warnings all through the manual it's still a bad design and they've got it back to front and it's dangerous and I don't think the damn thing quite frankly should be on the market so it was a good design concept but I think it was just poorly and dangerously in this case implemented and extech have got a lot of explaining to do and they need to fix it and if you've got one of these X Tech RC 200s I highly recommend you don't use it to measure voltage just use the tweezer thing just to measure passive components until expert X tech get back to us because I'm sure they will they're very responsive they seem very keen to fix some issues in their meters so I'm sure they will get back to us quick smart with what the real problem actually is I've guessed at it let's see if I'm right and um let's see if X Tech can fix it but until then don't use this thing and you know it's a real shame cuz I was actually starting to like this thing till it tried to kill me so my verdict on the X Tech RC 200 meter even though this wasn't a review because it was just a charred mess well you guessed it bloody trying to kill me

Channel: EEVblog

Views: 309,617

Rating: 4.8160815 out of 5

Keywords: extech, rc200, multimeter, meter, smd, resistance, capacitance, explosion, mains, measurement

Id: Ewyf9mzIfi0

Length: 12min 30sec (750 seconds)

Published: Mon Jun 14 2010