Could I get tips on how not to be overwhelmed going through a big circuit board?

Thread Starter

slashmaster2

Joined Apr 15, 2019
17
All my life I've had problems figuring out the overwhelming maze of a typical circuit board. Could be for a radio, a tv, a monitor, a fuel injection kit, a boombox, an amp, a roomba and most of all, the motherboard from a pc. Could I get tips on how not to let it all overwhelm me and how to break down what it all does? I already understand the part where power typically comes in, goes through a fuse, transformer, bridge rectifier, filter capacitor. and becomes filtered dc. I typically get lost in a maze tracing power in farther than that. Or maybe I'm better off tracing the power from the input or output of an amp for example? Maybe it would help if I use a marker to trace on the back of the circuit board all places I find positive power at full voltage?
 

SamR

Joined Mar 19, 2019
5,080
Back in the day it was Sams Photofacts. They are still around. Try looking it up online for your equipment. With a set of them I could do things the jackleg radio/tv repair shop guys couldn't.
 

Thread Starter

slashmaster2

Joined Apr 15, 2019
17
Back in the day it was Sams Photofacts. They are still around. Try looking it up online for your equipment. With a set of them I could do things the jackleg radio/tv repair shop guys couldn't.
You mean Sam's Technical Publishing? Guess you have to pay then.
 

SamR

Joined Mar 19, 2019
5,080
You mean Sam's Technical Publishing? Guess you have to pay then.
That's them. Search them online for your device. For some of the older equipment, there are free libraries of Photofacts. When I did a quick peek it seems they may have gone into the auto mechanic business. Back in the 70's you went to the local electronic parts dealer and he had them for the more popular models or could order for your specific brand/model. Those guys are gone since all the radio-tv repair shops disappeared. Not sure what is still available, but worth a few minutes on the computer to check for it. They had schematics and photos of the boards with test points indicated and the expected measurement for them. Laid it out really well and had troubleshooting information for the most common problems for that equipment. Well enough that I never used another repair shop back then, but that was before all the solid-state miniaturization we have now. Other than that it's finding a manufacturers schematic and block diagram. With the multilayer boards used now...
 

MisterBill2

Joined Jan 23, 2018
19,453
What always is very helpful is ti understand what a system is supposed to be doing. That has been my starting point for a large number of repair projects during my career. It can be very handy for the figuring out of what a circuit board is supposed to be doing, and then how it is doing it, and what each area does. LOcating the outside connection points is also very useful in that direction, as well.
 

dl324

Joined Mar 30, 2015
17,137
A well drawn schematic helps. Having an idea how the circuit functions and what isn't working also helps.

The usual troubleshooting steps are to start at the beginning and trace the circuit until you identify something that isn't working. Or the opposite; start with something that isn't working and trace the circuit back until it's working correctly.

My first job was testing refrigerator sized computers that consisted of about a dozen boards that were around 12"x10". The schematic for each board consisted of multiple E sized schematics. The way we troubleshot those was to find something that wasn't working correctly and trace it back until we found the defective component.
 

atferrari

Joined Jan 6, 2004
4,798
I did it once with an Epson printer ??850.
I traced first all relevant Common points and power (2 different values IIRC).

Then I went from steppers to drivers to logic glue IC to micro.

After that I was in condition of doing brain surgery implanting a 18F452 PIC micro. Worked at the first try.

I did draw my own schematic. The one in the Web is much much worse than the service manual. I found it when I was almost done.
 
Last edited:

BR-549

Joined Sep 22, 2013
4,928
Usually, by the time you pay a tech to trace out and draw a schematic..........Even before any troubleshooting is done.......It's cheaper to replace board.

It is not a common or developed skill for large systems.

And there are usually mistakes and left outs, from a trace.

There are ways to repair boards without docs........but to analyze without a print is very difficult.
 

BR-549

Joined Sep 22, 2013
4,928
I never thought much about it, but they might have image software that can analyze circuit boards. It wouldn't surprise me......might need the proper handshake to get it. Darpa and all that.

Others on here might know.
 

MisterBill2

Joined Jan 23, 2018
19,453
I did read an article about making scans of each side and then with some printshop magic producing a color composite showing both sides and the components. I never tried it but it sounded interesting. But with the multi-layer boards that could not work. I have worked with single sided boards with a bright light behind them. That works fairly well.
 

Thread Starter

slashmaster2

Joined Apr 15, 2019
17
Thanks for the replies everyone! I'm a bit disappointed it's not a developed skill. I've still need to try putting a bright light behind my circuit boards because I have definitely thought resistors came out someplace they didn't before.
 

dl324

Joined Mar 30, 2015
17,137
I'm a bit disappointed it's not a developed skill.
If you're referring to understanding circuit functionality and troubleshooting, it is a developed skill. It takes years, even decades, of perseverance to hone your skills.

When I graduated, I had never analyzed or troubleshot a circuit that took more than one schematic to represent. My first job out of school was troubleshooting a refrigerator sized computer comprised of TTL, aside from the memory chips, that took dozens of E sized schematics to represent the circuitry.

Some of the technicians who had years more experience were terrible at troubleshooting difficult problems. A number of them were just board swappers. They swapped boards until they got a set that worked, but never actually repaired a board. Boards that were particularly difficult to repair were marked as "dogs" and put back in the stock boxes. I was an eager student in my class (always raising my hand to answer questions), and my instructor took me under his wing and made the first computer I troubleshot one where every board was a dog. It took me the better part of a week to get it to pass testing. Because of that, I became acquainted with a large portion of the circuitry in less than a week.
 

Wolframore

Joined Jan 21, 2019
2,610
Identify different functional areas.

power supply - newer switching supplies are a challenge
outputs and inputs - are there sensors, motor, relays, switching .... etc
Control area - is it a microprocessor, digital logic or completely analog...
Analog circuitry - amplifiers, filters... etc.

If you don't have schematics, it helps to draw diagrams noting parts and values

At some point with some of the digital circuitry it's difficult if not impossible to know what the chips are suppose to do without some sort of reference or information about what it's suppose to do. Experience is a factor.
 

MisterBill2

Joined Jan 23, 2018
19,453
Certainly knowing what the whole assembly is important to know, and then understanding what the individual systems do comes next. Those are what you should know before you get to the board. Then looking at a circuit board you can look at the individual systems which are usually each in it's own area. Except some times they are not.Those make it harder.
 
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