Electronic know how

Question

When it comes to repairing electronics I to an extent have it under control. However, I can't do as many people do and look at a board and know what it is used for I just find the broken component and fix it. It is all good and such til you need to know how to fix a board that seems perfectly fine or resolder wires that became disconnected. I work in an area where there are no schematics for what I do. I recently had to learn transistors npn and pnp to get a clue (still am unsure about the blue wire). I still have no clue what the board does and that is one thing I would like to be able to figure out by looking at the board. I see people do it all the time they see the power goes in, goes through x components (I know the name of most) thus it equals this type of board thus if it seems to be doing this it should be x reason check-in x area. I just look and see if there are messed up components etc and hope that is the answer which isn't the case always. I have an X-box plug that I have no clue what went wrong (cheap ones). It has 120 volts coming in but not 12v coming out all parts look brand new the solder joints are crappy but no cracks. I have no clue what is wrong because I do not know the story entire of the board. I know it comes in 120v ac goes through a component eventually hits a transformer turns into the 12v and I dunno why the rest of the components exists. I know some smooth it out. I dunno what splits it into a 12v and 5v. I do not know a good way to test it without 120v coursing through it which I honestly do not want to do. I have a weird gap in my electronic know how is there a video series on how a board tells a story per se instead of just look for this to repair it. Sometimes I need to be able to figure out what a board does so I can fix it be it wires popped off, or an X box power supply. Neither have schematics and the x box power supply boards change from each one because of pricing. One was smothered in roaches so that one is probably obvious and the other was clean. Albeit after cleaning the roaches out the parts looked brand new, no bulging caps, no burnt resistors, the joints were shoddy but they were not cracked. Ben does a decent job of showing a talent like this he may do research I am unsure but I have seen others (bigclivedotcom) pick up a board and instantly knows that goes to x and go hmm... that circuitry is for w and this is for y but this one is an oddity on z it is probably used for A, and they just took it off something random without usually looking at the schematics. I do not even know why the companies choose some components they do instead of others that would do as good as a job or seem like they would. I am going to try and give you a pic of a board (bad quality but my phones camera is not the best) and you will see immediately what goes to what and how the board works and why it works how it works. I see a board that has parts I know how the parts work partially and I know where some wires need to be resolder back on and the rest of the wires will need to be probed to even figure out what they do and where to put them if I figure it out. I wish to have your eyes and brains to be able to instantly know this stuff. I know I have been redundant but I also I know I am not the best at explaining myself so I end up explaining myself twice in different ways hoping I convey the message. *Sidenote if it helps: This board goes to a Halloween decoration it makes sound and has two LEDs for eyes. The switch I believe is a double pole double throw you flip it one way it makes sound and lights up, you flip it another it just lights up. I personally almost feel the board is unnecessary if not for that chip hiding under the black resin. Which is most likely where the sounds are housed. I wish to repair it to firstly save money and secondly learn. That's about it. Thanks for any help. 
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shabaz · Answer

Hi Justin, What you're doing to seek to repair is no different to what most engineers do, i.e. just visually observe if anything looks out of place or burnt up. Most consumer electronics has no circuit diagrams, so it is near-impossible to be sure precisely how everything functions, and one wouldn't know the intent of the engineers who designed it (a whole team created it, so even people working for the company who designed the product won't know in entirety how it all functions without asking others, or looking in the documents they created during development. The experienced engineers can recognize certain patterns because they've seen them many times. A large complex circuit board is really comprised of smaller simpler circuits, all joined together. So, certain areas of a board can be recognizable (but not necessarily down to every single component). Also, with trends in the past few decades, it is expected that mass consumer items will be very integrated, and all the detailed functionality will be in just a few chips, so it is a black box as far as troubleshooting is concerned. Some parts are not replaceable like chips on board with a blob of resin. The good thing is that usually they don't fail (unless there is a flaw with the chip or the circuit design). Often the things that fail are interfaces to other boards or other products, due to connectors etc., or some parts which might be operating close to limits (for cost-effectiveness), such as certain capacitors, power supply modules, etc. When people probe with a multimeter/'scope, they are checking certain areas where they recognize the building block, and they likely already have an idea about what a particular input/output or supply rail should look like. I hope that helps. If you're interested in learning more about popular sub-circuits, any general electronics book should help. The book 'The Art of Electronics' is good - also has lots of photos to recognize different component types. To be honest even engineers who have studied for many years often don't like repairing some things that could sound simple to others, such as a kettle. I wouldn't know how to fix a damaged element, I've never owned a spare one, nor ever taken a kettle apart. And yet I'd have no issue designing something like a (say) electronic thermometer for measuring the temperature of the water in the kettle. In other words, designing is sometimes easier than repairing an unknown circuit. The designer has the luxury of choosing how the circuit is to work. To repair takes a whole different set of skills, such as being very visually observant and learning to recognize common faults.

jw0752 · Answer

Hi Justin,

I have to disagree slightly with shabaz . The Art of Electronics is a very good book but for the Electronics Repair person I would choose this book as it is more practical and more down to earth in its approach.

https://www.amazon.com/Practical-Electronics-Inventors-Fourth-Scherz/dp/1259587541/ref=sr_1_1?ie=UTF8&qid=1518196017&sr=8-1&keywords=Practical+Electronics+for+Inventors

It will give you the basics from the ground up and includes lots of drawings and circuits that can be wired up and tested. It does not have the depth of the Art of Electronics but sometimes too much detail can be more confusing than helpful.

John

jw0752 · Answer

Hi Justin, It sounds like you are well on your way to understanding what is going on. You certainly have the first ingredient, which is a healthy curiousity. Time and experience will help you as you continue the learning process. At some point you will be well served to get a good book and learn as much as you can about the basic components. One of the tricks that I use if I have questions about the application of a board is to use https://octopart.com/ to pull up data sheets on some of the larger key components on the board to see what their functions are. The board that you picture is an inexpensive micro processor board. All the control functions will come from the black box blob on one side of the board. It produces the commands to turn on the LEDs as well as generating any sound that the board produces. Other than testing the transistors and passive components and make sure that the connections are in good shape there isn't much repair possible on this board. Have fun with your continuing journey in electronics. Keep posting your ideas and projects here as I have learned that every time I post I learn new things from the really smart engineers on this site who freely share their knowledge. John

mcb1 · Answer

Like jw0752 and shabaz indicated, you are well on the way. For some of us it's been 30+ years of experience to reach this point and we've been exposed to lots of these situations. It doesn't always translate that years = experience and I work with some very knowledgeable people that I would suggest are at your level when it comes to fixing broken boards. I've fixed countless boards with no schematics, and the clue is being able to recognise what is broken/damaged or what it does/doesn't do. At some point you do need to be able to check that your repair has been effective. Every board needs power, and often it is the first problem. Later boards that use High frequency DC/DC converters (like your X-Box) have capacitors that have limited life and these wear and become ineffective, which causes issues. They tend to bulge or even leak. Identifying outputs that control the LED's (as in your example) means you can test that these are working without having to understand the inner workngs or programming of the micro-controller. Finally one skill you'll need is the abilty to produce a schematic from the physical items. It usually involves a couple of redraws as you tidy up your findings and work out the full interaction of the interconnections. Input on the left, output on the right, positive power at the top with ground at the bottom will help later when using it. Often you might only need a few parts to enable a repair. This skill gets better with practice and attention to detail, and identifying the parts requires access to datasheets or information about the components. Boards such as your LED with the COB (Chip on board) hide the controller and these can't be identified, so you're left to prove the outputs, LEDs and switch. I'm sure I could identify a number of boards by looking at them, and there are clues that you'll soon pickup. Most boards have a number or description that you can use in search engines. Some LCD monitors use generic manufacturers boards and simply add their logo on the front face, and these popup in forums, or spares suppliers. Cheers Mark

beacon_dave · Answer

I tend to find that seldom does one book ever cover what you need to know. Either it's just the style of the author, or the depth of cover of the information presented, but I tend to have to look at books by several different authors when trying to learn something new.

Quite often I find myself reading one book then I reach a point where it feels as if there have been several pages ripped out, at which point I will then typically refer to one of the other books in the hope that they have covered that area slightly better.

Alternatively some books are just a bit 'too heavy going' to start with, at which point I will typically switch to a book that covers the subject in a slightly lighter fashion, before returning to the more in depth stuff on a second pass.

I also find that the book needs to have a strong context in relation to the area I'm trying to learn about. So it is great to see examples which have some real world context associated with them alongside the theory.

jw0752 · Answer

Hi Dave,

I totally agree with you. When I attempt to learn more about a new subject or if I am having problems with something I will seek several books or sources as each may give me a different view. Unfortunately many of these books are quite expensive and that may limit access. For someone new to electronics I like to recommend the Practical Electronics for Inventors as there are used copies to be had for $20 or less. I should also point out that it is important to google the errata on this book as there are more mistakes in it than acceptable. The 2nd edition was particularly buggy. Fortunately a large group of electronics enthusiasts have still seen value in the book and its format so they have made a great effort to compile an accurate and comprehensive set of errata.

John

beacon_dave · Answer

Hi John,

Cost is indeed often an issue, although perhaps less so with core electronics than IT books where software versions update so frequently.

If you are fortunate enough to have a Safari Books Online subscription you can preview quite a lot of books before purchasing specific ones. Unfortunately it is a bit hit and miss as to which titles you can access e.g. Practical Electronics for Inventors is on there but The Art of Electronics isn't.

Dave

malus_lupus · Answer

Thanks for the advice. With this Halloween thing I realized I do not need to have the LEDs rigged how they are, and I found a motor that was not connected I know how to rig them to work somewhat proper the motor should pop up and down which means it should have a contact point that has a fluctuation between positive x and negative x but I have yet to find one I found one that goes from 0 to .x that seems more LED blinking lights than anything. I can rig the motor up with a double throw double pole reverse polarity switch if need be (it would be manual but I can deal with that). However, the audio oy vey I want that to work. I have it connected up according to what the board says speaker to speaker proper negative and positive but it refuses to work I even short the switch that goes to it to make sure it is always on while testing but nothing. Even if I jotted down the board in a schematic way I would not know exactly what to do for me to make the audio work. I have also discovered a very very odd thing on this that I have no clue what it does. It does not put out voltage, it is not connected to ground I do not think, however it does have 2 wires that come out of it and connect to a transistor. Here are some pics of the board. With some identity marks. I found where the blue wires go they are the speaker both are blue positive and negative it goes in the blue circle. The yellow circle is where the yellow wire goes from another switch presumably positive I have no clue where the negative for that switch goes it was disconnected when I got into it. I wired the board back together according to the pics I got of it before a lot of wires popped off bad soldering job cheap board etc. I however no longer need the eyes to flicker and there is no motor connection on the board as far as I can tell. Also the mysterious circle with green wires. I also will include a switch image so you can see how it was wired when I got it. (the speaker works I tested and found out once by accident way back at the beginning before the wires started popping off. Scared me because I had no clue it had speakers.Yes, a pad popped off sadly dunno when or how but it is a cheap board and the connection still works. It gets power all over the board minus the mysterious green area.) The

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