How To Read Schematics 3. Learn How To Understand Circuit Diagrams

hi guys welcome to learning electronics repair this is part three of how to read schematics in part one and two which I will link from the end of this video and also in the description we learned all about the symbols on the schematic diagrams that we are likely to find so really now if we think about the symbols as being like letters of an alphabet we understand the alphabet of schematics but there's more to it than that we need to understand how the components are connected together so in this video let's have a look at how the lines are drawn on the schematic these are effects for all the wires and the other information that we can also find on the schematic so here is a fairly typical schematic this one actually is an ATX power supply or part of one we can see here and you'll see lots of components on here the symbols that we went last time in the time before resistors capacitors diodes mosfets transistors and such like let's have a look at the information we have here so I'll zoom in on this section now you can see that the zoom on this PDF doesn't work very well it's a little bit fuzzy but it's okay we can see what we want so you'll note that the components have two sets of numbers by them for example we see D12 fr150 G18 fr150 the d18 D12 and such like this is the reference for the component if we look on the PCB usually we will find this on the silk screen printed on the PCB so we can identify which component to switch the other numbers FR 150 is the part number the type of part so if you wanted to replace D12 you would buy some FR 150 diodes you would look for FR 150 at your favorite components and buy it and that's what you would buy here's another one with ic2 l805 CV again ic2 is the component reference l805cv is a part number just one or two more so we have for example or 37 2.7 K or 38 2.7 K I'll just zoom it out a little bit it'll look a bit better there we go we have capacity C5 says One X 50 volt this will actually be one microfarad 50 voltage just the way they are showing it on here this schematic is using the different numbering system you might see this so example c23 says 103. it's not 103 it's one zero three and this means 10 followed by three zeros 10 000 or 10 nano fibers here's another one c19 says 104. that's 10 followed by four zeros or a hundred thousand that's a hundred nanofarads the difference schematic you may see that's done differently here for example we say r37 2.2 k 97 1uf so rather than this 105 106. this is actually tell you values in different ways another one C1 0.1 UF that's the same as 100 Nano farads on the other schematic that would be marked as 104. so one of the things you need to learn is how these systems work where they put in the values of resistance capacities for example the other thing we need to work is these lettering systems we have R for resistors C for capacity L5 for what is obviously an inductor okay so let's look at these various methods of identifying components on paper first let's look at the different methods we may find of marking the value of components resistors and capacitors in particular with resistors we specify the value in ohms we get resistors do from a fraction of an OHM to several Mega ohms or millions of ohms so obviously if we were to write the value out in full for example a five Mega Ohm resistor as five million ohms first of all there's lots of zeros it's easy to get confused you'll miss count them and secondly it takes a lot of space so to get around this problem we normally specify the value of a resistor either as a number of Ohms a number of kilograms which are 1000 ohms or a number of Mega ohms which is a million ohms and there's a few different ways we can do that so because for example I have a one ohm resistor like so or for example 220 Ohm resistor like so but this is a funny little symbol and you probably can't find that on your keyboard very easily that omega symbol so what normally happens that gets replaced by a letter oh so we will say one or one ohm resistor 220. or 220 Ohm resistor and you would find for example something like a one killer Ohm resistor use just put as one k okay 1K one Mega Ohm resistor one and so on now you will get some values and ohms and kilograms and megagrams that's all if that's what you written with a decimal point so 2 200 ohms is 2.2 kilo ohms and you will see this on schematics 2.2 K 4.7 k 3.3 Mega ohms that's the second way you'll see these specified with decimal points and because of that you could say for example some low value resistors so you may have 0.22 of an o 0.22 or 0.22 ohms so that's the way you often see these specified with the r the K or the M but quite often you'll find a shortcut on that as well so what a lot of schematics do to make this smaller if you like less characters they will replace the decimal points with the multiply k for one thousands M for one million R for one and you will see resistors that one 2.2 K being marked as two okay two four point seven k four k seven 1K well on the same basis one k zero yeah well I am one Mega room one m zero 3.3 mag well I'm pretty sure you're with us now three M three so those are the methods you will generally see resistors marked on the schematic what about the low value ones exactly the same 0.22 of a gnome zero or two two you just put the multiplier where the decimal point would be so that's how you will see resistors generally marked on the schematic what about capacitors well capacitors are measured in favorites but normally speaking a favorite is a very large amount of capacitance and you will not come across capacitors of this size on schematics probably the largest ones you will find will be Millie farids which like in thousands of a favorite but even those are extremely large micro farads or your millions of a fabric is most likely the highest multiplier you will see is wall 1 million Millions that sounds good one million millions of a favorite that's a one to the power of minus 12. yeah 11 zeros in front zombies so we actually take pick a favorite in our case as being one one p f it doesn't make sense in the moment when we get up to a thousand pick of farads we go to the next multiplier which is nano fired okay so one nanofarad equals one thousand Pico Fabrics after that when we get to 1 000 nanofarads we go up again to micro farads that is a millionth of a firewood this is a thousandth millionth referred yeah so what micro farads and fats one thousand Nano fabrics and the last one not a likely to see is MF and Millie farage which is one thousand micro farads so that's how the multipliers work with capacities again there's different ways to Mark these and you saw some of this on that schematic I was just showing you so in some cases you will find values like 10 microfarads or 100 Nano farads these sort of markings and you will find them like I was just sharing you where they put the value one zero three so that is 10 Pico fibers with three zeros after these equals 10 nanofabets okay this is why we have those markings 104. this is 10 pickup if I was with four zeros afterwards which is a hundred thousand ten with four zeros I'll draw that to make it clearer 10 with three zeros ten thousand so these are the two markings you will see you'll also see the 2.2 micro farads and you may just occasionally come across components marked like two you two so that's using the same method that resistor was replacing the decimal points with the multiplier yeah let's look at um 2.2 Nano farads 2.2 Nano farage could be marked as two and two yeah or we could also be marked as two two that's 22 bigger farads with two zeros after it which is two thousand two hundred kickoff hours which is 2.2 Nano farads so that's how the system works with resistors and capacitors you'll just need to get your head around this probably a little bit hard to take it and one goes somebody probably explain this a lot better now I just did but that is something you need to learn how the values are marked on the schematic let's look at something a little bit less mind-blowing though these are the component designator letters or reference letters if you like this is where we see on our schematics or 102. or 33 these are the reference to the components on the board these letters will give you a good indication of what type of component you have and these are the ones you'll commonly see this is not everything and some manufacturers of boards or of this schematics use different methods but I'll give you a good idea so or as a resistor VR is a variable resistor quite often a Tremor port or a preset is more VR also that's what they usually do with them we have some slightly less usual ones or V is a various or mov metal oxide this is a voltage dependent resistor but sometimes you'll see the monsters vdr as well depending on what the person who is making the schematic wanted to do varista th see this one sometimes is a thermistor then we have capacitors C capacitor doesn't matter if it's polarized or non-polarized capacitors really I always see VC variable capacitor that's one you may come across and doctors Al and closely related to this one t Transformer f b fairy ice B's this is a small inductor usually in fact always Fair like bees shall we keep going why not F fuse SW or sometimes s switch or l really just off my page let's go over to here where we can see them here P plug TP what do you think guys test point JP jumper J I'm using all the combinations here yeah Jay there's a jack or a jackpot sticking with the passive components X or x t a l or sometimes y as a crystal not so many left now d tired LED is light emitting down so obviously I won't even write it down ZD and occasionally Z is a Zen usually ZD op opto isolator and then we have transistors now transistor regardless if it's a mosfet or if it's a bipolar transistor on Old boards they were probably marked as TR and our newer ones is q okay both of these are a transistor you cannot tell from the designated if we say mosfet or the bipolar transistor or any other type of transistor that's the ones they use and the last one are integrated circuits on Old schematics I see and on newer ones yeah these are an integrated circuit oh I see that is a myth that you for IC stands for unrepairable I'll leave you to work out for yourself if that actually it's just an urban myth or if there's any truth in it but that's why they say you for integrated circuits wouldn't repairable as to what Cube meant I really don't know there's one other thing I'll mention related to this as well and that is you'll often find these markets and I'll explain why especially with modern components you will have a little chip for example like this with six legs on each and inside it is like a dual mosfet or the Dual transistor so we'll have effectively like two transistors in one package which all the lights that you cross over and you will find similar things like this where you have eight pin devices and you'll have a dual op amp so we'll have enough amp in here get into there we'll have in order connected to there okay usually in the schematic you will find that the two or pumps or the two transistors in the one package are drawn in separate places on the schematic where they fit in the wiring no reference to the fact they're in one package but you will know from the schematically part of one package because if this for example is q11 on the motherboard transistor 11 that's half of it all the other off depends how they did it will be called Q one one a and this one will be q11b so when you see this the same reference With A or B you know it is a dual package the same with this dual up amp you'll have U1 a as you have u1b and if it was a quad op-amp you also have u1c and U1 G so that's the way you will find it's marked when there's more than one iteration in an IC effectively logic gate if you have six logic gates all the same that could be like u5 a down to u5 F okay so we know all we need to know really now about the way the components are marked on the schematic let's look at how the lines or the Y's are drawn here is a schematic we're looking at a little bit earlier the ATX power supply and you'll see there are lines drawn everywhere these show the connections between the components now you'll see the lines cross over each other but sometimes they cross over each other with a DOT where we see the dot it means that those two lines connect to each other so we can see The Collector of Q2 here goes to the emitter of q1 it also goes to the junction of these two diodes T5 and D6 one end of this resistor onto a tap on the coil so where you see these dots it means the two ones join where you see this they just cross over they do not join there is an old way of doing this which I'll just show you now in case you come across it's on Old schematics in the old method you would find this so you would have a track coming down and where the truck doesn't join chewies it will go like that okay you'll see these sort of things that sort of thing that shows the wire is not connected that shows it is connected there for example so that's the old method of Germany and depending on what you're working on if you're working on Vintage or retro equipment you may be working with vintage or retro schematics so you should be aware of that method also sometimes on the schematic especially with digital equipment micro processor microcontroller based equipment you'll have many many lines all heading in the same direction and often these are shown as a force a data bus so you can see here we have some thick heavy blue lines on this schematic if you look you'll see coming here we have some lines with arrows the arrow actually shows the direction of the data and we have names key power LED Green Key menu and such like we have some coming the other way okay and we have another one here and if we follow these heavy sets of lines you'll see this goes up here it picks up some extra signals here P 5.0 da zero and such on which join in look the dot is showing that that is joining the thick one this thick one is called the buzz this is a date impossible okay so you can see that those signals are coming from this chip and joining the buzz and this goes up here and we can see for example gpio general purpose IO zero to seven H data zero to three so there's eight of those and three of those and if you're required this is actually going well you can see we have three plus eight one two three four five six seven eight and three okay that's the signals there as you can see similar here another data boards with four signals going to the audio up here okay at one out two and this is kind of saying output left output right but it's the same thing basically so these are data buses and you will find these on some schematics but there's another way of doing this which was used more as the complexity of these circuits increased and that's to use Nets here is a schematic which uses Nets or net names again we have the arrows pointing in and out and we'll also see bi-directional arrows like these ones which tells us the signals pass both ways on those and we have lots of names of the net so net plus usbp on net minus USB P2 and so on just by the names we know this is USB data it's telling us that this is PCH or platform control Hub data this is going to the PCH this is what used to be called the North Bridge on a motherboard as you see numbers to the size 54 49 49 and so on four these numbers actually tell us which page in the multi-page schematic those signals go to and sometimes you'll see more than one number if the signal is going to various places and not just one place this schematic also uses data buzzies we can see here and this is challenges it's MDB some databuzzle or the zero to 63 so we have 64 bits of data on this one let's go into page five also quite nicely on this schematic it's showing us what is on this page the dim slots and the CPU so we know basically what it is and it's times here this is DDR3 Channel B and this is the type of motherboard this one will show you the PCH or parts of the PCH USB we were just looking at so there's a lot of information on here to help us to understand the schematic and now of course to the part you've all been waiting for we understand the symbols we understand the lines that join them together but how do we read schematics well there's no one answer to this but I will give you as much information as I can and I'm sure this will make a lot of sense to you first of all with schematics there are three types of electronics if you like and the three types of electronics have different forms of schematics and the amount of information we can work out from reading the schematic will vary and the methods will vary depending on these main types so the main types of circuitry are analog and digital I said there was three chaps which I've only written two and that's because we're going to break them up a little bit analog circuitry is basically any circuit where the voltage across the components varies in a free manner so the voltage can be for example if the supply voltage is 12 volts voltage is on there can be anywhere between 0 and 12. if the supply is plus or minus 15 the voltage is anywhere on the circuit could vary between plus 50 and minus 15. this is analog circuitry these are your radios your amplifiers your TV sets and lots of vintage equipment and also some coolant equipment is analog also included an analog circuitry as something that may surprise you which is portsworth modulation now you may think oh but pwm is done by microcontrollers well yeah it is these days but that's just a microcontroller doing what we used to do with analog equipment in the 70s and 80s yeah for example it pulls with modulates I'll just show you this what supports with modulated well you probably know it varies the width of the pulses depending on some input conditions like a power supply needs more power it monitors the voltage the voltage goes down therefore it increases the width of the pulses so the mosfets that are driving the power supply but in actual fact pulse with modulation is completely on one technology just look at this op amp amplifier very common analog components plus or minus out okay out is driving our transistor which is driving our power supply okay minus is merely non-inverting uninverting inputs on the non-emergency Sawtooth wave this is just an awesome way to generating an analog waveform okay on the other one non-inverting via a feedback system we measure the outputs of our power supply okay resistors of course were involved in this as well but that's what we basically do well look what happens this is comparing the two voltages so imagine your feedback voltage is and I'll get a different color pen your feedback voltage is that level okay what's happening every time we go Sawtooth wave and this input goes above that voltage on the output we get a pulse okay if this voltage increases because the output voltage is increased so it's now here every time the Sawtooth goes above that voltage we get a pulse but look the pulse is much narrower okay the output voltage goes down it's now down here somewhere what's happened to the pulses now they're much wider I'll try and draw it better there you go okay do you believe me now puts with modulation is an analog technique it's not a digital technique it's just the Micro Control always thought they could do it better with software okay so analog circuitry amplifiers audio or ref circuits and such like ports with modulators how about digital circuitry well I said there were three main types one was analog and the other two are digital or subsets of but in actual fact I don't count very well because I've just realized now there's four so on the digital we have discrete logic can't spell it very well discrete logic these are your logic gates and Gates or Gates nor Gates and such that's discrete logic did I spell it right the first time I think I did okay the street logic then broadly speaking we have microcontroller circuitry or microcontroller controlled devices and we have Micro processor circuitry and devices these various classes will affect very much the way the schematic is drawn and how you read the schematic if you're wondering the difference between a Micro Control and the micro processor device well basically the microcontroller is a microprocessor but it also has its built-in memory it's built in eprom it's Ram if you like and the various ports that read various inputs and control various outputs so with your microcontroller if that's the way you have in here just a black box if you like you have various inputs which are monitored some sort of program which is actually making the decisions and you have some outputs and that basically is any micro controller based circuit micro processor well with a micro processor you would have external ROM or eprom you will have external RAM volatile memory and you would have peripheral devices I oh input output devices for the microcontroller it really does is puts all that into one box again the ROM will effectively control what the device does these i o devices can be monitoring various inputs and control with various outputs and that's basically a micro processor based device and again this will affect the schematic and how much use it is to you when you're trying to fix stuff anything really example a graphics card a GPU is just this you have your GPU just a good example it has Ram it's ours run the BIOS it's us inputs and outputs to your pcie and it's ours outputs to your screen HDMI or whatever it is but that really is just that yeah it's just that so those are the main types of devices you're likely to come across of course you will come across hybrid devices if you like as well so you may have an audio mixer with analog inputs audio inputs analog outputs but somewhere in the mixer we'll have a digital audio process Inception which is one of these types so yes you're gonna add hybrid devices as well I think that's quite a good example with the mixer so how does this affect the way we read the schematic the way we understand the schematic let's consider how to read schematics in general and then look more specifically at these three types of devices or four types of devices I was just talking about so a schematic is like a map if you like it's a diagram that shows you the circuitry and how it all connects together and all the components that are on there meeting a schematic as an analogy it's a bit like reading a map you have a map of the UK now say for example you wanted to go walking in the countryside or driving in the countryside from point A to point B would you look at the map of England and try to understand the whole map of England everything the whole lot yeah even including the Welsh or would you look at the bet you're interested in a bit that's relevant to what you're doing well I'm fairly Stewie you wouldn't spend hours examining understanding the map of the UK you would look at the part you want to drive or walk in yeah and the same is very true with schematics if you're reading a schematic because you want to repair a device it's probably the most common reason don't think you have to read and understand the whole schematic you don't what you have to do is identify the part of the schematic that is relevant to the problem you have and understand that part of the schematic that's the first important thing about reading schematics another thing with reading schematics believe me a schematic is not a silver bullet having a schematic for the device will not necessarily enable you to repair that device yes it can be a help or an assistance but sometimes you need all the information as well the schematic alone will not enable you to repair that device to be able to understand a schematic at all the first thing you really need to do is understand the basic principle of how the device works if you don't understand how it works you're not going to understand what the schematic is trying to show you I mean the circuit designer do you think he understood how the device worked the principle before he drew the schematic yeah of course he did and you have to do the same thing you have to understand how the device Works before you can read the schematic let me give you a good example of this a radio receiver okay a radio receiver most radio receivers which are analog circuitry work like this so you have an antenna coming in you have an of amplifier which amplifies this signal and then you have a mixer the RF signal feeds into the mixer and also feeding in you have an oscillator this is called a vocal oscillator and these two signals produce an output and the output is the difference between the two frequencies so the local oscillator is always let's say 450 kilohertz higher than the incoming signal as you change the oscillator frequency you effectively select an RF frequency 450 kilohertz above it and this is a basic principle it's called the super hat receiver and you'll understand what I'm telling you all this in a minute okay coming out of the mixer you have an i f or intermediate frequency this is the difference between the two quite common 455 kilohertz and that frequency will have on it the music the audio the speech that you were receiving this then goes into the if amp so this is Amplified and then goes into what's called a detector debt my friend that's just laughing around the corner and coming out of the detector is the AF the audio frequency this goes into the AF amplifier and that drives your speaker okay that is how your radio works now if you were to look at the schematic for a radio and not understand this is how it works you will not read that schematic you will not understand that schematic what's all this stuff doing you have to understand how it works before you can read the schematic so the first thing if you faced with a schematic for some device you're repairing you have to Google or another way look up how does this work how does a cassette player work how does a color TV work how does a radio work if you don't do that you'll never understand yes this is work guys this is work and gradually as you work on more devices you'll already understand how they work I can draw this out I know how that works and because I know how that works it then enables me when I look at the schematic to say oh this is the mixer this is the oscillator this is the if stages and so on yeah so that's the first point to read schematics you must understand the function of the device obvious sure does everybody think about that no in addition to understanding how devices work and I don't know how everything works I go and Google it's like I'm saying you guys have to go and Google it to get a basis of what you're doing what you're working on okay the other thing you need to understand is how components work how does a transistor work not like all the electrons and holes in the cell you can doping you need to understand what it does basically if hypo positive voltage on the base of an npn transistor it will turn on Etc okay we also have to understand how components interact with each other and I'll give you a good example with resistors and capacitors but this is by no means exhaustive list it will just give you an idea of what you need to understand about all sorts of components to read schematics properly so resistors we know they valued in ohms and they obey something called Ohm's law and you do need to know Ohm's law if you don't know this one you will not get very far the relationship between voltage current and resistance and some basic formulas if you want to know the voltage cover it with your finger or thumb voltage equals current times resistance if you want to know the comment comment is voltage divided by resistance if you want to know the resistance voltage divided by current so that's something you need to know you also have to understand how resistors work together what they do when they put in series and parallel there are some basic rules here I can give you some idea so for example on a schematic if you find a lot of high value resistors in series something like this and you'll probably find this in power supplies or anything with a switch mode power supply get over to the ports with modulator chip what a MAG what mag what mag for example those resistors are part of a startup circuit this will have something like 320 volts on from here to ground will be a capacitor and this is like a basic building block you need to understand building blocks like this so high value resistors and series are almost certainly dropping a lot of voltage high to low charging a capacitor and this is effectively a startup or a power circuit for a chip one other thing on resistors we talked about high value resistance in series being in startup circuits normally you'll quite often come across something like this where you have several I can't just be worn low value resistors going in parallel to ground usually some sort of Supply voltage here going to a in fact we'll be here let's put a transistor in nice make it a bit of a circuit okay switch mode power supply something like this yeah go into some sort of monitoring circuit what's using off amp again ouch some voltage on here yeah if you see this sort of thing we can use some low value resistors for example three 0.22 ohms in parallel this sort of arrangement is always a current sense so you'll find circuits where they monitoring the voltage across all over value resistors you know straight away or you should do now there's a common sense circuits and from this type of basic building block that's how you start to learn to read the schematics to identify what parts of the circuit are doing voltage dividers this is something else you really need to know about because you'll find this all over the place when you have some voltage from something and two resistors in series like this going to something else quite often up amp but it could be anything really okay this is a voltage divider the voltage divider is quite a simple thing to understand what you do have to know what it is so when you see a couple of resistors like this in series voltage divided it's putting the voltage on here that some division of the incoming voltage so that's 10 volts and these are the same value as each 10K 10K actually the voltage that will be half that because of the same value it's a very quick easy way to work this out basically what you do is you add the two resistances together so we'll call this all one or two so 10K let's put some different values on 3.3 that's like a standard value okay so if you want to know what the voltage is here you can do it two ways you can say okay well 3.3 is roughly a third of ten so the voltage here will be a third of that and you'll be right actually the other way you can do is if they're not quite so obvious values as that let's change them a bit 4.7 K yeah it's a bit less than half isn't it but the way you work it out is you take turn and you divide it by the sum of the two okay which is eight and you multiply by whichever resistor you want to the voltage across probably this one the ground times the value of R2 3.3 k shall we see what he says well it's actually 10 volts divided by 8K times 3.3 yeah 4.12 a bit less than half because what we said yeah sometimes you need to know what the voltage is sometimes you can just see oh a bit less than half and then you know that on the other input of this input voltage goes higher than that one the output of this apartment will go up towards the supply Rail and if it goes lower than that one it'll go down towards ground or the negative Supply rail so these are the sort of building blocks I'm talking about basic stuff like this I'm not going to do this in depth in this video because it's not the subject of this video but if you want me to teach this let me know and we'll have some more lectures okay another good example fairly simple one capacitors capacitor passes AC box DC normally speaking if you have some voltage rail or similar and you have a capacity to go into ground what this is doing this is called decoupling and it's effectively taking the Ripple or the AC signal to ground it does smoothing whatever is on here if we have the other way so you've got some air and you've got some out this is called a coupling capacitor what this does well if you had this is not volts and you are so AC waveform up here that's on the DC offsets or the center of the waveform says 5 volts it will remove the DC components and coming out of it you would have that yeah on zero assuming there's a negative Supply by the way in your device okay otherwise it can't go by zero so the main use of capacitors you'll find is for coupling and decoupling really the only other one probably that they use for is something like this we just uh capacitor to ground and some sort of positive Supply yeah out came into something or other let's have another op-amp why not when you switch on or whether voltage appears here maybe some signal turns on this capacitor will start to charge up via this resistor the amount of time it takes to charge or will depend a on the value of the resistor the higher the resistor the longer it will take the value of the capacitor the larger the capacitor the longer it will take but gradually the vulge on here will come up and when that goes above the voltages on that one the op-amp will switch okay so this is often used in time in circuits where you want something to happen a certain amount of time after something else happened yeah like some output from something put a voltage on here and then this will effectively give you a delay and put the output there so there's the main use of capacitors and this is the sort of thing I'm trying to explain about understanding basic circuit building blocks much the same applies and power supply type circuitry DC to DC converters book Regulators you've heard them called No Doubt where you have something like this you need to understand how this works so we have a mosfet some positive Supply a controller Portsmith modulator another mosfet going to ground the two join together drive a coil which ask your passengers on the output and this is out okay this is if you like V in in out and this effectively is a voltage regulator the supports with modulator and these are the building blocks now do you understand something like DC to DC converters there's a number of variations of this you will find I'll just give you one other example something like this coil diode capacity to the ground Moss Factory rounds pwm this is what's called a boost converter this actually gives a higher voltage out here than what's coming in this is used in the PFC or power factor correction circuit and you need to understand all these different types a good way to learn something like this is to go and look up on Google something like DC DC converter apology underwater for smps topology and you will find something like this so this is smps dot us I will link this in the video description if I remember I'll try and here we have for example the converter topologies book boost flyback Cork sepic and all sorts of other ones okay these are non-isolating converters these are your switch mode isolated converters so if for example you're trying to repair it power supply is much more power supply you have the schematic what you don't you understand how it works you can refer to something like this so what you need to do is find an example that looks basically the same as your power supply you can see they're all different if you have something which is like this you say oh I have a push pull I was supplied once you know that you can then go and Google for how does a push-pull power supply work or how does push Port smps work and that will give you a lot of information about how it works this is what I was trying to say if you don't understand how it works you will not understand the schematic once you do understand how it works everything is there for you so that is another method which you'll have to employ when you want to learn how to read schematics another weapon in Your Arsenal is this one which is data sheets so any ICS on there on the schematic you will see the part number but if you don't understand what that IC is doing again you will not understand the schematic but you can go and enter the port number into Google Plus the win datasheet and you will find something like this typically you will get an example circuit which will probably look very similar to your schematic in fact and you will also find a block diagram of what's Happening inside the chip if you need that but probably more importantly is something like this so here we have a list of all the pins on the chip FP feedback inverting input to the amplifier this pin is connected directly to the output of the regulator by a resistor divider and sets the output voltage so with this data sheet if this is the chip on your schematic and your output voltage is wrong from this you will be able to determine which pins you should be looking at on your device you should be able to mesh I mean what's happening on the feedback the chip isn't running there's no output it's not working from this we can see we know where the power comes into the chip does it have power it has power but it's not oscillating we can see where the resistor controls the oscillator maybe the resistor is open circuit so this is how you can start to understand the the schematic so guys data sheets topologies very useful things let's have a look at an example of a schematic for an analog device so this is an audio mixer normally when you're looking at annual schematics the input will be to the left hand side of the schematic and the output will be to the right so this is a convention with schematics analog anyway that the flow of the signal is that way okay this one's no exception we can see here we have an input mic and line we have some transistors some op-amps and if we look at this we should be able to find the signal path so basically the signal comes in here let's say a microphone or music okay and you can see that that basically comes in this way through some stages of amplification and into an op amp after these transistors well we have the gain control here this is your volume control basically for that channel you can see there is an LED here level setting if you look at it this is making some sort of comparison between two signals there and there okay it's driving an outputs we look a voltage divider resistors at a certain level it will switch this transistor on and that turns effectively this led on or off so this is the first things you can just work out from a schematic like this one where's the signal go well it also goes through this capacitor into this op amp out of this one to here insert this is where you plug in like an effects device an echo machine or something or you can just switch it so the NCAA doesn't being used the signal now comes into here look this is your tone control whoa middle High yeah you can see them all here this is actually the low one okay through the term control through another op amp and then it goes out to monitor so for example if your level set LED wasn't working just all you can get this you can print it won't save a certain we need to look at the output of this op amp and we need to look at this part the circuit so this is what I'm saying about we only really need to look at the part of the schematic that we're interested in okay so that's an example of just how to read a analog circuit schematic with digital ones it's a different matter here is a schematic of a typical micro controller based device I know it says micro processor but this is a microcontroller and you'll see there's no signal path with this type of device this basically is the brains of it and it has inputs and outputs so depending what's happening on some inputs it can control signals on various outputs and that's really controlled by the program this is running with a schematic white this you can't really determine how the device works because without knowing the contents of the program you don't really know but what you can say is that we can check for signals on various inputs and outputs if we knew what the program was we could say for this sequence of inputs we should have this output but without that we can't so the only thing we can really do here is for example if something isn't working like the pump for example we can say well that's controlled by the signal here so this signal here turns on this thyristor so This eventually goes High turns the thyristorant and turns the pump on which means we can check things like the thyristor these resistors make sure we don't have an open circuit somewhere and the same applies in this area I mean this is the power coming and we have some high value resistors plus the 40s Avenue a diode a couple of diodes so this is just dropping down the input Mains voltage this is AC this device here TVR this is a voltage dependent resistor some events against voltage spikes basically we can see it diodes which rectifies the amazing capacitor which charges up a z a diode which maintains a voltage here and this goes up to vdd this is the power to the Chip And to reset so I can see just glancing that this this eventually from the 27 volts it tells us produces a 5 volt rail another Zen and more capacitors so when you first switch on the five volt will come here through this resistor and it will charge this capacitor going to ground so we can see that vdd eventually as its capacitor charges maybe a few seconds depends on the value of that in this maybe part of a second we'll put power on and you can see here reset so this is active low it has a bar over it okay so as this comes up reset goes high that means the reset function stops working the processor starts running and starts doing its work but all we can really see other than that is obviously this is some sort of input here we go uh probably monitoring things on the thermostat the heater and such like and that's basically a Micro Control what based device with something like this if the microcontroller isn't working or isn't sending the right signals at the right time the chances are there's nothing you can do about it because apart from getting a scrap one and taking this part off and open it works you can't fix that okay this is why it's called you uh you whatever unrepairable okay but if there's some problem with one of these parts of the circuit this transistor is obviously switching and relay here that's doing something water tank Illuminator then you can work on those parts of the circuit so the schematic will help you when we come to a micro processor based off it gets even worse here is a motherboard uh gigabytes uh sniper 5 or G1 sniper okay now this gives us a block diagram so we can see how effectively everything's connected up the DDR Ram goes direct to the processor PCI Express easier PCI slots connecting directly to the processor uh some of them go into the PCH platform control Hub various other things connecting here the land Saturn and so on the 3D sounds IO ports so you can see how this is effectively made up and you can see various parts of the circuit so yeah we have a schematic okay with lots of signals on but can we use this to repair a motherboard if it won't start probably not and the reason is you need to understand how the motherboard starts up and this schematic won't tell you that so with a motherboard or a graphics card another perfectly good example of this you will have a power on sequence so power rails have to come up in a certain order and this is quite complex this will involve communication between the PCH the LPC this is your super Io if you like those two chips together probably with the clock generated chip and the circuitry that is generating all the voltages for this which is not shown on here to power things up one after another in the right sequence and make sure that each power rail comes up and is stable before the next one all that you need to understand to be able to repair the motherboard if it won't start and therefore you need to know the power on sequence for that chipset you can Google it and maybe you will find it and if you can find that information then you will know which signals to look at so you'll know where it starts what happens first what happens next a power on sequence looks something like this and guess where I found it on my channel of course so this is for h81 chipset for particular motherboard and this will apply for all motherboards with this chipset but it won't apply for all motherboards of other chipsets so we can see if we look at this we have a sequence of numbers one two three four and so on and this is telling us what happens so when we plug in from the ATX power supply we have 5 volts standby okay you can see that goes to effect and generates another voltage 5 volt dual through another Fat generator another voltage three volts dual and eventually generates this signal or SM or St okay on PCH deep power okay so these signals are generated because all of these voltages are present okay once that happens it sends a signal to the super IO you can see here it also sends another signal sleep signal and so on so you can see what actually happens if you look at this you can watch my video this one it will tell you what's happening here but basically to understand or rather to be able to use the schematic for this you need this you can see after six next thing happens is seven somebody presses the power button after they press the power button this chip sends a signal back power button pressed okay and then we have a step nine is it's on here somewhere yeah it sends a signal to the power supply ATX power to the power supply Powers up and sends the signal that power okay this is what you would need to be able to use a schematic to repair this motherboard without this information well the schematics not really any use to you and guys I did say at the start of these three videos I would teach you how to read schematics now I hope you can see that reading schematics is quite hard work so learn to do this you have to put the f is in to understand a schematic you need to understand the function of the device or the general level if you don't you will never understand the schematic even if you understand the function of the device with this sort of micro processor-based system then you probably still can't repair the device using the schematic because you don't have the other information you need the power on sequence for example if the motherboard won't boot up so you can see that a a schematic is not a silver bullet B reading different types of schematics will give you different sorts of information and you do it in different ways and three that the schematic alone is often not all that you need especially with this complex digital equipment okay so I do hope you believe I did teach you how to read schematics but as you can see the hard work is now yours to do I've given you the method I've told you how to do it but I can't do it for you yeah you have to go and apply that now but having said that I think we will have a part four so what I'm gonna do now and only you guys who watch this through the end will know this okay I'm gonna make one more video maybe 60 Minutes depending what so I'd like some of you guys to go away and submit some schematics to me I want to mixture of analog microprocessor a microcontroller based circuitry and just send some to me I need to know what the schematic basically belongs to yeah unless you really want to challenge me and let me see if I can work it out so send me some schematics you can email them to me I'll put the address on the screen now okay so email me some schematics and then I will look at those I shall select some possibly the ones I like that we've got of most yeah and we'll do them on video we'll just have a look and I'll tell you what I see and that's schematic and how and why I see it and then I think really you guys will be able to get off on your own and do this okay so I hope you enjoyed that I hope you send me something I'm also liked and I will definitely say who sent the schematic air yeah your username your subscriber name so hope to hear from you guys I hope you did enjoy that get to the comments anyway let me know what you think about these videos and I look forward to seeing you all soon on another within your choice repair video ciao for now guys

Channel: Learn Electronics Repair

Views: 27,214

Keywords: learn electronics repair, learn electronic repair, electronic repair, school, lessons, course, training, free, fault diagnosis, trouble shooting, troubleshooting, pcb repair, component level repair, circuit diagrams, schematic symbols

Id: OirYfphm7nI

Length: 68min 48sec (4128 seconds)

Published: Fri May 19 2023