Novice trying to understand circuit boards and how they are built

[komrad2236]

Hey internet, novice here.

I am trying to understand the concept of how circuit boards are built in hopes that this knowledge can help me understand how to approach the repair, and find the fault easier.

I've been repairing some stuff, looking at some diagrams, learning.
But based on what I see so far, let me run this by you.

Basically, seems to me that, circuit boards are built around few ICs that are supposed to do the job.
The rest of the components are there only to transmit power and signal to these ICs, and away from these ICs.
If an IC needs 5v, and input into the board is 100v, there must be some components that can lower this voltage so IC can use it and not get damaged.

Lets say some type of a video device is not outputting any video.
I can then look at the chips inside this video device, see which one has the job to process/output the video signal, first test if it is even powered and then test its video output pins.
If the chip is not getting any power, the problem is with the power line leading to the chip.
Then I just narrow the problem down until I get to the issue itself (cold solder join,failed component,broken trace,...)


Did I get the concept right or am I missing something ?
Please, point me to the right direction where I can learn what I need to understand this better.

[Grandchuck]

You are on the right path.  Checking to see if chips have power and an input signal is where lots of people start the troubleshooting process.

It will help to learn basic chip functions.  Take operational amplifiers as an example.  They are a basic building block and you could invest some time to learn how they are used.  Other examples include voltage regulators and others.

[ledtester]

Indeed, if you watch electronics repair videos you'll notice that the first thing checked out is the power supply. Sometimes a device has multiple power "rails" -- e.g. 5V and 3.3V or +12V and -12V, and each of these are checked for the correct voltages.

A repair schematic may also show the expected voltage at various places in the circuit. This is especially true of older analog equipment.

Most electronics may be viewed as transforming an input signal to an output signal with the signal going through one or more stages, e.g.:

Input --> A --> B --> C --> Output

If you're not getting any output signal or the incorrect signal at the output it helps to probe at the input of the last stage -- i.e. at the input of "C" -- to see what the signal looks like there. Continue backing up through the stages until you find what you expect and you've located a stage which has a problem.

When assembling a circuit it can be helpful to build it in reverse -- i.e. from the "C" back to "A". This is especially true of devices which have audio output because you can inject a test signal into what you have completed so far and listen for the expected output.

[Terry Bites]

It’s worth finding out what goes into designing a pcb. Get hold of a free package and design a simple pcb. eg www.pcbway.com/project/shareproject/KiCad_files_an_automotive_LED_flasher.html
There are numerous CAD packages.  They all use the same processes.
They are-- schematic capture>net list creation>"rats nest"> placement> track routing> output files (photoplotting CNC parts list etc)
Components have a graphical and a physical form. The CAD will have libraries of these and they will let you customise or create your own component.
https://www.circuitbasics.com/make-custom-pcb/

There is usually plenty of rip up and retry to get the optimum component placement and routing.
There will be "forward and backward modification" which allows changes made on the pcb to be reflected back to the schematic and vice versa.
Routing can be automatic or manual but it’s mainly a mix of both.
Reverse engineering requires unpicking the routing and how it runs between parts. It can be very time consuming!

[EPAIII]

Been at it for a long time and the best advise I was ever given was, when you have a problem, mentally draw a box around the problem. One or more of the signals that come out of that imaginary box show the problem.

Then you check all the inputs that go into that box. If one or more are not correct, then your box is not big enough so you enlarge it until all the inputs are OK. With all the ins OK and the out(s) bad your problem must be inside that box.

Now, mentally cut the box in half - more or less. Check the signals between the halves. If all are OK the problem is in the second half. If one or more are bad the problem is in the first half.

Keep dividing the bad box in half until you have narrowed it down to a single component. Replace that component and check. The problem should be fixed.

When people talk about checking the power supply or power supplies first, they are just checking the inputs to a mental box. That is usually a good first step as power problems are frequent. Don't forget that a good ground is part of the power supply system.

There are other shortcuts. Electrolytic capacitors are infamous for failing. It is always a good idea to look at them for any signs of trouble: bulging ends, leaking, discoloration are all possible signs of trouble. But sometimes there are no visible indications. Another frequent problem is bad solder connections. These can often, but not always be visible. Crimped connections can also be bad. Resistors can overheat and change value: they can change color or even become cracked. It is always worthwhile to give the PCB or overall device a good visual inspection before starting with meters and o-scopes.

[TheNewLab]

For troubleshooting you got it and the suggestions already are great.

for troubleshooting, vids are great, if you prefer a book

https://www.amazon.com/How-Diagnose-Fix-Everything-Electronic/dp/0071744223/ref=sr_1_4?keywords=how+to+repair+everything&link_code=qs&qid=1665972857&qu=eyJxc2MiOiIxLjM0IiwicXNhIjoiMS40MiIsInFzcCI6IjEuMjUifQ%3D%3D&sourceid=Mozilla-search&sr=8-4
Is a great book, new or epay used, or other sources.

If you want to study the concepts:
 Behind the semi's and circuits. the Gold Standard remains "Art of Electronics" it is in-depth, but seems to be the must-have book, and works for quick reference are electronic principles questions. Also "Electronics for Inventors" although he/they are not the best type checkers, each edition so far has some errors,