PCB FAULTS: How to TEST & FIX

before we use a meter we have to test it and  there's two things that we need to do number one   see down here it says category 3 600 volts only  these meters are allowed to go inside these   boilers for repair the next thing we have to test  the meter itself and we do that by simply going   over to ohms and you can see ol open line and  then an m ohm so that's millions of ohms and   it's in auto ranging mode which we have to be  we're not allowed to use any others so the next   stage is going to be i'm going to make an x here  on these probes and within two seconds that ol   has to go to zeros full stop and then a number  that number has to change within 10 seconds we   do know that some flukes don't do this and some do  we don't understand why because of us the rep and   he doesn't know either nobody knows some models  do some models don't all of these have to so   let's do the first testing we're going to make an  x and press hard and there we are two seconds and   it's refreshing let go two seconds it's got back  to ol that's a perfect multimeter ready for use before we can begin fault finding and seeing  what's wrong with the boiler we need to make   sure that it's off and dead and no voltage is  going through and that's called a four-part   electrical test and they consist of number one  is earth continuity and that means that that big   fat green wire coming into the house continues all  the way to this screw because that's where we pick   it up to the casing the second test is going to be  short circuit the third one is resistance to earth   and the final one is polarity and that's when we  switch the boiler on but no demand to see whether   the 230 volts or more is actually on the brown  live the neutral is zero and obviously the earth   is going to be zero so i'll do each chapter  separately so let's go back to the beginning   i've removed the fuse and here we have checked  it you must do this every single time you go into   the house because we are riddled with boilers  and they have 13 amp fuses which blow up pcbs   so you don't want to be liable for that the next  thing is we need to check whether that screw   is actually earthed and the way we do that is  simply always the black lead will go to the casing   and the red lead will go to the screw and as  you can see immediately i've got zeros and   it's been refreshed which means that the earth  is continuing with no resistance all the way   from that consumer unit you also move the red lead  onto the pcb earth where it comes in on the flex   and then you also go where the yellow and  greens meet on the boiler casing so there's   three places we do it and that's before you do  anything else to make sure that we've got a good   earth and now we can continue to the next  stage the short circuit test is a very simple   but very important test and what we're looking  at is the resistance between that live terminal   and the neutral terminal coming in  so it's measuring parts of the boiler   we need to turn the multimeter onto ohms it's  quite safe because as you can see the padlocks   there test the meter yes that's working fine and  as always we have to put the black lead in first   and then finally the live to there and we'll  give it a moment or two to calibrate itself   and it's now reading 53 ohms now normally  as in the book that we have here page   14 which is our short circuit test  we're asking for 100 ohms or higher   but because there are different ways of  plugging in the different components onto   a pcb it could go as low as 20 ohms so if  you do read between that live and neutral   for example 60 ohms in theory that would be a 4  amp fuse and the way we calculate that is very   simple we use ohm's law and we have an app which  is completely free of charge it's the yellow one   here's a cutaway and what we do is enter into the  voltage side 240. into the resistance that we've   got 60 and then when we calculate the answer  comes back as four so it's only six is into 24   is four that means that that fuse will  definitely blow and possibly damage the pcb   and other components so please download the app  and use it because it's there for your benefit   if you have that less than 100 ohms please  phone the factory before you do anything else   and ask for guidance say i'm doing a short  circuit test i've got 53 ohms is that okay   or is something wrong and they may say right  that is wrong it should be a lot higher than that   therefore you need a new pcb  and you would be wise to replace   maybe a fan or a pump or another component  before you do that because that could be damaged   with the new pcb so don't use a reconditioned one  it has to be the latest version from the factory   for the model of the boiler that you're working  on so that covers our short circuit test so this is an example on a valent boiler  and as you can see the boiler is unplugged   and the multimeter is in the off position so we  do exactly the same as always put it onto ohms do the test 2122 resetting so now as always the  black lead has to go on neutral so we'll put it   here on n put this one on l for live and it'll  calibrate itself and it's giving us a number of 14   m so that's 14 million ohms which is way way  higher than the 100 that we need and that's a pass   so the board has switched on as before so nothing  changes but that's how we do it on a valent boiler   and all the other boilers are exactly the same way  and that's what we teach here on a wednesday so   all the engineers have to do this with a plug or  with a spur to make sure that they're really good   and then when they leave here they know exactly  how to protect themselves and stop blowing up   pcbs so that concludes our short circuit test  resistance to earth is a test that we have to   do it's the third and final one in ohms and  we're measuring whether the integrity of the   live and earth and neutral and earth has  been broken and what we have to see is ol   over a million ohms if we see numbers then that  component that we're measuring is now failing   quite fast and we can do that on any component  here that has live neutral on earth for example   the pump but we can also do this test on a washing  machine a kettle a microwave anything that has   live neutron earth we can do this resistance  to earth test so let me show you how it's done put it into ohms press the two terminals  together and that's fine and the first   thing we always do of course is to put the black  lead onto the earth casing and we measure the   live first and we want to see ol and we've  got ol then we want to test the neutral side   and we see ol and if we  went to the earth connection   you can see here it's jump straight to zero  because it's earth to earth in two seconds   proves that it's continuing so that's how we  do it on a worcester boiler and that's a pass on the valent boiler we do the same way but our  earth connection is here on the bottom corner   don't use the white casing  because that's insulation   must be where the yellow and greens meet and as  before we'll put this first on the live terminal   and we see ol put it on the neutral terminal  ol put it on the earth terminal and immediately   it shows us continuity and that's  how we do it on a valent boiler   all right just to show you the close-up version  so we put the black lead into neutral the red   lead into live and you can see here it's gone  to 244 243 and then we let go then the next   stage is we put the black lead onto the earth  connection and we go into the live terminal   and we get that 243 244 because it will move  because electricity does then we put it into   the neutral and as you can see here is 0.027  so that proves that the wiring and the polarity   in this house going to this boiler is perfect  and that's how it has to be so here's an example   of a non-condensing boiler still doing the same  three tests so we'll put the multimeter into ohms   get the probes short it out and that's the pass so  the first stage is going to be earth continuity so   black lead goes to the casing readily goes to  the earth connection and we can see we've got   zeros which means the earth is continuing with  no resistance the second test is going to be our   short circuit so again black leader will go to  neutral red leader will go to live and then we'll   just wait a few seconds for the multimeter to  calibrate itself and it's reading 280 ohms and you   can see the one and the two's being refreshed so  that's the pass the next stage is going to be our   resistance to earth so we go back to the casing  and then we go back here to the live terminal   and we expect to see ol but we don't we're seeing  280 so alarm bells are ringing something is wrong   so we'll put this into the neutral setting  and there we can see zeros so that means this   is a complete failure because a neutral wire is  touching an earth wire so if i was to plug this   in and switch it on the board would definitely  blow up and maybe take another component with it   so this is a really good example of the four part  electrical test and it's failed on the third part the final part is called polarity and that's where  we can plug the boiler in but the boiler switch is   in the off position because we don't want it  firing up while we're testing so we just want   to know how much electricity we've got and where  is it so first of all we'll use our contact list   and that tells us yes we've got some sort of  electricity going in so we need to move this to ac i'll do some close-ups black lead goes to neutral   red league goes to live and you  can see here we've got 244 volts   and that's fine but i don't know which one of  the two wires are carrying the voltage and the   way we do that is we put the black lead on earth  and we leave it there not on the casing here on   the earth where the yellow greens meet and then  we go into the brown wire and here you can see it's 244 and that's fine now we have to test  the blue neutral so we put it into the neutral   and we can see here zero and it should  be zero many installers are mistaken they   they've been told and it's on youtube's everywhere  that you can have five volts on the blue and   that's problem three that's completely wrong the  householder needs to find a part p electrician   to bring fat five volts or whatever volts  there are to zero you are not allowed to   recommend anybody because that makes you liable  jointly with the electrician who has to do this   it's their fault it's badly wired house nothing to  do with the heating nothing to do with the boiler   but the upshot is if we have two three four or  more volts on the blue one main fault will be   this zone valve or any diverter valve it doesn't  matter who makes it it will go halfway and stop   and you'll think oh i'm brilliant i've all i've  got to do is change that little synchron motor   and i fix this you've got no chance because that's  not the fault the fault is voltage on the blue   the other big effect will be the pump if this  pump doesn't go to full speed in in a millisecond   and it has to trip a sensor or a switch  whatever they use and if it doesn't do   that in that millisecond you'll get an error  code saying you've got no water or change the   pump or even worse change to pcb which is  why we have this four part electrical test   so i hope you've enjoyed it and uh subscribe to  our channel and thanks for watching and take care

Channel: Mr Combi

Views: 31,125

Keywords: Fernox, Vaillant, Baxi, Ideal, heating geek, Alan Hart, stuck pump, vent a combi, filling a combi, filling a system boiler, Vokera, Worcester, water gauge, low pressure, vent rads, PRV leaking, air vent leaking, Grundfos, Danfoss, Honeywell, Drayton, F.22, F76. condense pipe frozen, leaking boiler, how to, mr combi, training, fault finding course, apps, fault finding apps, noisy boiler

Id: OxlqhZVOdNI

Length: 15min 24sec (924 seconds)

Published: Sun Mar 07 2021