Sherlock Ohms - Page 1
Forum section: electronics / repair

author: Zero_Ego
author_rank: Regular Contributor
timestamp: December 15, 2020, 03:29:13 am
content: Reading Schematics an analysis und etwas Analogies.Hi,Typing to some excellent technicians here on the forums - it occurred to me that reading schematics is a real skill.Some are able to reason out even if they don't fully understand what they are looking at. It's a kind of a creative art where even if you don't understand, you pause asking yourself 'what does that part of the circuit do?' You many not always get it correct, then other times it soon becomes clear - purely by thinking it out logically with reasoning.I am curious on what you are seeing when you look at a schematic. Do you use the water analogy?One of the things that trips me up is the inverse proportion to resistance. They are labelled backward in my mind. Something so simple. Lower the resistance higher the current but the terminology, speaking for myself, gets muddy.Low impedance that one always gets me. "what = high current slow down you're going to fast. . . "Again just a curious question about what you see when you look at a schematic. Maybe you all have your own method. Or are you just doing pure maths?If you are so busy with the maths how can you analysis a circuit . . .answer your gunna need a lot of spare time. And possibly have OCD. (Just a tinge)When you look at the fundamentals of different transistor, common emitter common collector and common base, what do you see? Anything, maths or water? Spacecrafts? Pareidolia?Ohms law?Sherlock?Conventional current flows vs electron flow? These crittersrunning around?I'm pretty sure you all have different methods. I would be interested to read about them.Any mental tools or methods you might care to share?Thanks in advance.ZE

author: bob91343
author_rank: Super Contributor
timestamp: December 15, 2020, 05:02:10 am
content: I try to separate the stages to find familiar circuits. Only conventional current, no electrons, even though sometimes it is electrons.Look at impedance levels to estimate currents and power. Make simple calculations to guess at voltages.Is it an oscillator, amplifier, comparator, or what? It doesn't always work but it's a start.My best skill is probably troubleshooting. I look at the diagram and imagine what could go wrong that matches what actually is wrong. And compare it to my experience. I read books and have trouble finding many that are well written.

author: ledtester
author_rank: Super Contributor
timestamp: December 15, 2020, 05:37:35 am
content: QuoteI think it's too unreasonable to try to figure out how a circuit works entirely from first principles. Usually you have an idea of what the circuit is supposed to do and a general notion of how it is supposed to work. Schematics are composed of smaller electronic building blocks that you learn to recognize and reason about, and analyzing a circuit in terms of these building blocks dramatically simplifies understanding how the circuit works.Lots of schematics follow tried and true designs and vary only in certain implementation details. Linear power supplies, for instance, all have the same overall operating principle and that makes a lot of troubleshooting and repair possible even without a schematic.

author: Zero_Ego
author_rank: Regular Contributor
timestamp: December 15, 2020, 06:19:10 am
content: Quote from: ledtester on December 15, 2020, 05:37:35 amAs opposed to those other explosive devices the SMPS. I have seen guys walk away from a table when one tech says to the other "I think I've fixed it" . . . those things can explode. (Is it just me?) That happened to me.The first switch mode I even repaired. The guy even ran to the mains power board, ready for the fuse to trip. I switch it on wow. It feels good when you have a win repairing something so complex and without an schematic. Sometimes you win some other times they can bite. Warning flash capacitors in cameras. My God they pack aThanks for your kind comments guys. I love reading them.ZEEDIT: "I read books and have trouble finding many that are well written."Good books that don't wander off into the maths like Floyd. Well written electronic books great question, are there any?Yes surely but there is equally amount of badly written books. This could also be said to those that teach electronics. Good electronics teaches are hard to find - if you do - you are lucky. Some are on another planet all of their own. Like programmers.EDIT: "Schematics are composed of smaller electronic building blocks that you learn to recognize and reason about, and analyzing a circuit in terms of these building blocks dramatically simplifies understanding how the circuit works."Yes so true.It's our ability to understand those building blocks each on its own a mountainous task. When you throw in wave forms, with digital logic try to marry the two harmoniously.Question.Does anyone see a benefit to the electronics industry as a whole with the introduction of the SMPS?

author: bob91343
author_rank: Super Contributor
timestamp: December 15, 2020, 07:09:46 am
content: I have been building SMPS units of one sort or another for over 50 years. In fact I claim that I am the first radio amateur to use one in a mobile installation.Yes they have certain usefulness, if only to create engineering jobs and sell transistors. They are necessary to meet efficiency and standby power requirements imposed by regulatory agencies.They do create fireworks sometimes.

author: Zero_Ego
author_rank: Regular Contributor
timestamp: December 15, 2020, 07:24:46 am
content: Quote from: bob91343 on December 15, 2020, 07:09:46 amUnreal. That's mind blowing. That takes some serious skill.(I know where to come for SMPS questions)I'm willing to pay.I really admire that level of skill.Excellent comment.ThanksZE

author: Zero_Ego
author_rank: Regular Contributor
timestamp: December 15, 2020, 11:37:56 am
content: If know one has even told you to visualize a schematic as something more than just a drawing on paper, that's how you will always see it. just a bunch of symbols doing nothing.You bring the drawing to life. Otherwise it's just ink on paper.Sheet music is a good example of ink on paper verses human interpretation.Just shootin' some thought out to the Ethos, along with logos and pathos. (I know who knew, 'logos pathos' gOOgle)

author: madires
author_rank: Super Contributor
timestamp: December 15, 2020, 12:34:49 pm
content: Basically you look for known patterns, i.e. building blocks or basic circuits, to get an overview. After that you look at single blocks and values of components. And with some experience things become easier and you also get a feeling about which values are reasonable without grabbing a calculator.

author: Zero_Ego
author_rank: Regular Contributor
timestamp: December 16, 2020, 07:36:30 am
content: Quote from: madires on December 15, 2020, 12:34:49 pmUnderstanding a circuit diagram verses troubleshooting.Would it be fair to say that having the schematic is a luxury few get to see.Regardless, things are getting so small, components tiny to the human eye. We will all end up visually impaired. A lot are now using microscopes w/ mounted HD camera - to see the circuit. Move your soldering iron into frame and it looks like a lamp post, adding more fun and games to the challenges of such fine work.Technicians are like doctors in a lot of ways. You have to know how each part of a circuit talks to the next.Sadly under paid doctors!ZEP.S Hello to Dr. Watson

author: madires
author_rank: Super Contributor
timestamp: December 16, 2020, 10:39:39 am
content: Quote from: Zero_Ego on December 16, 2020, 07:36:30 amThere's a tendency to keep the schematics a trade secret. But based on the type of device you might find a service manual including the schematics somewhere in the Internet.

author: mzzj
author_rank: Super Contributor
timestamp: December 16, 2020, 12:00:05 pm
content: Quote from: ledtester on December 15, 2020, 05:37:35 ammany SMPS also start to look more or less all the same after you have repaired &designed dozen of them.After few you don't even care about the schematicspower supply with UC3842 wont start = controller dead as nail (shorted) and controller supply cap dried outticking = short on output or the controller supply cap dried outetc

author: CJay
author_rank: Super Contributor
timestamp: December 16, 2020, 02:13:17 pm
content: Quote from: mzzj on December 16, 2020, 12:00:05 pmYep, that's about it, for things like PSUs, the 'secrets' you need to know are that almost all of them work and fail in the same way and almost all of them are *really* close to the reference designs in the controller chip datasheet.Proper schematics are great, they 'flow' and you can track down inputs, outputs, functions etc. but it takes practice, you learn to spot functional blocks and you find you can get to a point where you can look at a schematic you've never seen before and be able to recognise enough to home in on the bit you need in a few seconds.Funny thing is, once you've got a bit of experience you'll be able to spot functional blocks on circuit boards too.You do need to have an understanding of how the components work but for the most part it only needs to be basic.I'd like to say you get a gut feeling but it's nothing so fanciful, it's just practice, knowledge and experience, doesn't take long either.The fashion for schematics to be a collection of chip pinouts with no interconnecting lines drawn between them is hateful, it works for autorouting and PCB design but it's a time wasting nightmare for fault finding, repair, even general curiosity, I find I spend far more time searching for the labels and lose the 'flow' of the circuit.

author: shakalnokturn
author_rank: Super Contributor
timestamp: December 18, 2020, 01:03:04 am
content: Quote from: Zero_Ego on December 15, 2020, 03:29:13 amThat's one of the problems I run into on paper I tend to look at transistor arrows to get a quick clue on the way thins flow.I'm used to the bipolar transistor more than any and that works well with conventional flow, I learnt quite early about valves so although it's not quite as natural as looking at a bipolar I easily switch to electron flow when looking at a valved schematic.Now when I'm tired and looking at or (worse) drawing a schematic with both bipolar and MOSFET in both polarities I just find the whole thing a pain to see.

author: David Hess
author_rank: Super Contributor
timestamp: December 18, 2020, 02:54:19 am
content: Quote from: Zero_Ego on December 15, 2020, 03:29:13 amSchematics are a language like reading sheet music or an additional natural or programming language.QuoteIf what is going on is not apparent at first, I look at voltage levels being pulled up or down.QuoteI see impedance transformation.

author: srb1954
author_rank: Super Contributor
timestamp: December 18, 2020, 03:49:21 am
content: Quote from: Zero_Ego on December 15, 2020, 03:29:13 amI start out interpreting a new schematic in terms of trying to figure out the signal and/or information flow through the circuit.You look at the various parts of the circuit and partition them into blocks that perform a distinct processing function on the signal and figure out how the signal or data changes as it flows through the whole circuit. In some ways this is a higher level, more abstract, view of the circuit where you are not so much concerned with what the electrons are doing in each part of the circuit but what are the signal characteristics in terms of wave shapes, frequencies, data patterns etc and how those characteristcs change.Only when you have fully understood the signal flow patterns can you usefully look deeper into the blocks of circuitry and figure out what each circuit element does and how the voltages and currents around that part of the circuit that make it work to process the signal.

author: babysitter
author_rank: Frequent Contributor
timestamp: December 22, 2020, 04:30:34 pm
content: Staring mostly on my own schematics (lots of similarities) for the last 13 years I realized that I am somewhat out of training of reading other peoples schematics. I'm still active with the local repair cafe which helps but there is some decline. That made me thinking....isn't that something where gamification could help?The game should present a unknown circuit with a hidden standardised description and the task for the player would be either attaching the right description to components or a block of the schematic. Points for correctness and speed. A manual variant of that I am trying to improve myself.BRbabysitter

author: Renate
author_rank: Super Contributor
timestamp: December 22, 2020, 05:39:10 pm
content: Quote from: Zero_Ego on December 15, 2020, 03:29:13 amWell, there is a thing called conductance, which is the reciprocal of resistance.It's usually not spoken of much.We do kind of have these traditions like the idea that current flows from plus to minus.Maybe we should have decided that the electron has a positive charge, it would have made life easier.In any case, voltage and current are like two sides of a coin.Most statements about either one could be turned around to say something about the other."The sum of currents into a node is always zero." => "The sum of voltages in a loop is always zero."Take a 12 V battery. Nothing connected. What's it doing? Nothing. Power = 0 WattsPut a 3 Ω resistor across it. Current flow = 12 V / 3 Ω = 4 A, Power = 12 V * 4 A = 48 WattsTake a 4 Ampere current source with the output shorted. What's it doing? Nothing. Power = 0 WattsInsert in the loop a 3 Ω resistor. It develops a voltage across it = 4 A * 3 Ω = 12 V, Power = 4 A * 12 V = 48 WattsInsert in the loop a 5 Ω resistor. It develops a voltage across it = 4 A * 5 Ω = 20 V, Power = 4 A * 20 V = 80 WattsOk, but a battery can only deliver so much current, right?A current source can only "accomodate" so much voltage.We can't have anything having infinite power!Insulators and conductors, are also two sides of a coin.We live in a world where insulation is cheap and conductors have to be specifically made.When I make a little flashlight, I need a battery, a bulb and two wires.I don't have to go out of my way to insulate anything.When the aliens who live in pools of mercury want to make a flashlightthey'll need a battery, a bulb and at least one insulating sphere (containing the ambient mercury).

author: cdev
author_rank: Super Contributor
timestamp: December 22, 2020, 09:20:47 pm
content: If you did a good challenging game, it could become a huge aid to people wanting to learn electronics. Because people remember what they do much more than what they read or see.Quote from: babysitter on December 22, 2020, 04:30:34 pm