Convert Your MULTIMETER into an accurate SHORT CIRCUIT TRACER Finder for less than $1 Build This DIY

hi guys welcome to another learning electronics repair video uh i recently made a video regards uh million or micrometers and they're using tracing short circuits and i tried two meters i'm pretty sure a lot of you saw this video i will link it from this one um so i bought two um millio meters which actually would read down to 10 micrograms both the same resolution one was 75 euros approximately and it was 37 euros approximately and the more expensive one proved to be very very efficient to find in short circuits but the the cheaper one was not very stable it had the same resolution but it didn't have the stability so it couldn't give you a good reading and i couldn't recommend that meter that was the wire yr2050 the vc480c course the other one i thoroughly recommended so i thought today i'd try a little experiment to see if i can effectively make something that's better than the the yl 2050 was for almost nothing so um first of all let's have a look at the circuit board i used to test the other meters so this is a strap graphics card and i've actually sold it onto this um a short circuit so you can see here there's three banks of capacitors these three banks are all in parallel the other ones are in parallel but not in power with these so you can see here i've actually put a short circuit yeah and i was tracing this with the uh million micrometers i can find it quite clearly um so i just want to show you how to do this on you know like western the euro almost nothing in fact you can probably find the salvage parts of this and literally do nothing so this is uh a multimeter the anion and 808 so if i put this onto resistance range and i'll just uh i'll put the light on so you can see it and we'll set it to manual ranging on ohms let's see that if our multimeter can also find the short circuit so first of all let's see if we can determine which column it's on so we go across the first one and see what we read we read point ones it's just setting that let it settle okay 0.10 what's this column width this is the one that actually has the short circuit on it and yet it's reading 0.16 so it's not even finding the column let's go to the third one point one one point one two so this meter actually will not find the column with the short circuit on the fact it actually resulted so let me explain why it's actually reading higher on the column with a short circuit and how we can actually improve this so we just find some paper yeah okay and i'll zoom the camera out a little bit one moment when you use a multimeter to measure a resistor or a short circuit basically your multimeter sends a current through the resistor so from your meter probes you were connecting across to the short circuit device or the resistor okay and between your probes is the resistance yeah and you are measuring this resistor so your meter sends a current through the resistor okay and it also measures the voltage across the resistor and ohms or v i r in the triangle as i always show you okay r equals v over i i equals v over r v equals i times r remember that one and you always go to where it was all so the resistance is v over r yeah so the meter knows the amount of current that's going through the resistor it knows it's sending it so it knows exactly how much current is flowing it also measures the voltage across the resistor so it knows what i is yeah r equals v over i he knows what i is it measures the voltage and that's how it calculates a resistance but the thing is it measures the resistance here yeah on the end of your meter probes that's where it's measuring the voltage sorry let's say he says it's measuring the voltage on the end of your meter probes and your meter probes will have some resistance so the meter although it knows how much current's flowing it doesn't actually know how much voltage drop is in these wires and the more current that's flowing through them the more voltage drop there will be so when you measure the voltage here it can't work out an accurate result it can't work out what the actual resistance is accurately because it can't compensate for the voltage drop in the wires and in fact when you get to very low resistances short circuits as you value resistance almost zero when you get to very low resistances the resistance of the wires can be more than the resistance of the near short circuit or short circuits so more current flows down through here into the lower resistance which gives more voltage drop and i suspect that's why there's meter on the column of capacitors where the short axis is reading slightly higher because the effect of the resistance of the wires becomes more pronounced as you increase the current so that's why the meter can't read low value resistance now there's a way around this and this is called the kelvin probe and this is what those other million micro emitters are actually using so the way these work and i did briefly explain this on the previous video but i'll do it again so here's the meter yeah these are four connections yeah minus current plus current minus i plus i yeah plus volts minus volts now what happens is now the meter sends the current through the current wires into the resistor that you are testing the short or near short the voltage is actually sensed on these wires which come to the same place [Music] so what's happening now is the currents flowing down through this circuit around yeah but the voltage where it's measuring the impedance the input of this is probably like 10 mega ohms so the current that flows through this circuit v plus the v minus is almost zero it isn't zero but it's so close to zero that the voltage drop down these leads is no longer relevant now it's no longer a factor and that's why with the four wires it can measure exactly the voltage there and there not the voltage it sees here and here on your two wires so that's how those meters are working and that's how they're actually doing it so given this i came to the idea we could use a very simple circuit and emulate this using the multimeter so the circuit i want to use is using a device called lm317 which is a voltage regulator uh one amplifier or one 1.5 amp voltage regulator i think it's one i think it's 1.5 doesn't matter and we can use an lm317 to make a circuit called a constant current generator and to do that we just need the lm317 under resistant now let me just show you how that works this is an lm317 and it has three pins on it so i'll just draw it for you okay three pins one two three uh this pin is called adjust adj yeah this pin is the out and this pin is the air so you see the voltage in here the voltage comes out here yeah that's how it actually works and that's this way up as i'm showing you so we can use this as a voltage regulator but we could also use it as a constant current generator and the way we do that as we feed the volts into in yeah i'm actually going to use 4.5 volts and the reason being is because that's the voltage that the vc the one we tried in the day this one that's the voltage this actually outputs i can measure the voltage coming out of this and i can say it's 4.5 volts so i'm going to use the same 4.5 volts this is out and we connect a resistor from here to the the just pin adj yeah that's it up sorry guys i'm just interrupting my own video here because i made a mistake so i'm going to draw this circuit again uh so continue from where we just were we've got 4.5 volts coming in we've got the adjust and the out pin and the resistor we connect is between out and adj and i'm going to use a 22 ohm resistor resistor will give us an output current of actually 57 milliamps the reason i'm using 57 milliamps is because the vt when i look in the manual tells me that on the lowest resistance range it actually generates out 100 milliamps and on all the rest it's 50. yeah so i'm going to go close to what's giving out um to get 50 milliamps you actually need about a 25 ohm resistor which is not a standard value so i went with 22 ohm which is a standard value and that's the way i choose that and then from here is your output and this is a constant current source 57 as i say milliamps okay so that's the circuit now let me show you how we're going to put this together so the first thing we need to do this is a multimeter and the multimeter needs to have a millivolts range now this anand an808 is quite inexpensive maybe 20 euros and this actually has um a resolution which is effectively four digits yeah so this will actually read if you can see yeah two point zero zero one millivolts okay depending on the ranges it's all too big i can actually set it to manual range on it yeah so we can do that so that's the meter that we're going to use i could use my uh fluke multimeter well this only gives me to point one yeah so use a meter something like the ang something that's got a bit a bit of resolution to it yeah i would actually recommend this meter but there's plenty of of similar ones so that's the meter we're going to use we need two meter probes yeah and we need an lm317 and a 22 ohm resistor now i've actually soldered this one many together so what do we have we have a piece of wire connected to the in terminal yeah we have the resistor between the out and the adjust just like it shows in the diagram here that's the resistor yeah and then we have the wire on the out okay and that's all we need so the first thing we're going to do with this let's find a few more bits i didn't mention we need two of these so these are basically just from these terminal blocks and i've just taken the inserts out of two of them yeah it's quite a chunky one this needs to be big enough to go over the meter probe and you'll notice that the meter plate is not long enough to come through one so if we use one of these we can do it this way so we'll just um adjust these outwards so it will slide in so there's our meter probe which now goes through okay and attaching to this we want the out i've just i've got solder on the wires to make them hopefully get a good connection so we take the wire the out into here and we want the meter probe sticking out the end now we will just take a screwdriver and we will tighten this up okay nothing high tech about this guys nothing high-tech i'm just easy with my fingers actually and then tighten it up with the meter with the screwdriver okay so there's our regulator if you were making one look permanently out of a spare meter probe you can actually just take a little cable tie a zip tie and fasten this onto here so it stays here and this is where the voltage end comes in so that's one of them the negative lead is even more simple so with the negative lead we just need a uh again one of these and a bit of i'm using black wire so again we put this on here push it as far as it will go so the probe is sticking out to the end so that's our two meter probes so again we can just uh tighten this up okay there we go nice and tight so that's the negative we can now attach the the probes to our meter and we set it onto millivolts so we just attach the cribs the meter and the last thing we need to do is to put voltage under here we'll use the red to the positive now you could use i would suggest uh three a a batteries or even aaa batteries in there but i mean bear in mind this is going to give you about 50 milliamps but you're not using it continually yet but you do you need a phone or five volt supply you could use a little five volt power supply i'm using my bench power supply set before the half volts but really it isn't that important you just need to get the voltage under here in that sort of voltage range yeah batteries would be a good one okay so we've done that so let's see if our meter can now find the short circuit first of all does it know which column as the short one so we'll just go to the the first one and we read across it and we're reading 0.2 80.279 yeah we'll now go to the next one what's this one really this is about 0.25 two four eight so that's not what you're reading lower what's this one reading two nine six that's not a bit higher so again it's showing us that the middle column does have the short there's five capacitors there's a little one at the end as well so we'll start with that one let's go to this small one that's reading two times two next one two 60 259 252 250. next one about the same 254 this is where the short is uh 196 this is the one afterwards 231 230. so this meter this thing which i just lashed together for like the less than one euro is finding short circuits down to the capacitor in the block and that my friends i think is very impressive uh i don't know i've seen anybody else do this before um it just occurred to me after the last video was it work and yes it does work i mean you can see guys it works there's a couple uh ways we could modify this one in particular so i'll just show you on the diagram effectively the resolution of this will depend on the current that's flowing so the more current that's flowing the higher the difference in the readings you'll see um so what you could do with this is you could take from here another 22 ohm resistor and connect a little switch between here yeah so you can do that if you wish and then you can switch this between about 50 milliamps and about 100 milliamps which is what the vc does when you're on the lowest reading if you did dart you should see well twice the current so you should see effectively twice the voltage drop and you would think that the difference between like you know a bad column and a good column would be even more so so by switching to the resistor in another 122. you're pretty much doubling the resolution of the meter so that's one thing you could definitely do to change it the other one would be to increase the voltage but i've set this deliberately to the voltage that this has now you might think well fs you've got four and a half volts on it if you like stick it on to like something that's got v core or some device that only works at like 0.9 volt you might damage it i'd be interested to know what people think but i don't believe that's the case because if you connect this to something like a v core v core for a processor or a gpu probably draws 60 amps to several under the vamps for a high powered one so you sending 50 milliamps down here the voltage here will instantly drop this will limit the current to 50 or 100 and the voltage you see here will drop down to like 0.9 anyway you you know whatever yeah i probably wouldn't get lower than that because that's the voltage drop you see if you use a test meter on on diode mode yeah so i don't believe it would actually damage devices okay guys so there you go one uh ghetto method of putting together a very sensitive uh micro ohmmeter notice it's not measuring the resistance by the way it's just giving the voltage drop across it but when you short circuit finding you don't really care what the resistance is all you want to know is where is the lowest resistance and this without a doubt will tell you okay guys i hope you enjoyed that short video and i'll see you all soon on the next one adios amigos

Channel: Learn Electronics Repair

Views: 247,493

Keywords: learn electronics repair, learn electronic repair, electronic repair, school, lessons, course, training, free, fault finding, diagnosis, component level repair, troubleshooting, inductors, short circuit tracing, short circuit finding, milliohm meter, microhm meter, Vici VC480C+ revire, short finder DIY, short tracer DIY, short locator DIY

Id: P_2GGNr4q1s

Length: 19min 44sec (1184 seconds)

Published: Mon Feb 28 2022