Author Topic: Question about tracing circuits  (Read 279 times)

matmosphere

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Question about tracing circuits
« on: May 06, 2021, 05:15:21 AM »
Does anyone have a good resource for tips getting started with tracing circuits. I have a fairly complex pedal that is working and a schematic that is close but not correct. I would like to see if I can figure this one out.

Some kind of tutorial? I figure my multimeter continuity tester will probably come in handy.

culturejam

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Re: Question about tracing circuits
« Reply #1 on: May 06, 2021, 07:33:35 AM »
I've done a fair bit of tracing in my day. I usually start by removing the PCB from the enclosure and photographing both sides of the board. Then composite the two images in Photoshop (or whatever) so you can see both sides at once. Make sure you keep the same distance to the board with the camera to make lining it up easier, but it will usually require some massaging to get it lined up. Then you can see pretty much all connections (except for traces on the top that run under an IC). Then just start drawing...or in your case, verifying with the schematic.

Here's an example that is on FSB but that nobody every actually traced:

matmosphere

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Re: Question about tracing circuits
« Reply #2 on: May 06, 2021, 10:05:27 AM »
Thanks CJ, that looks like a good place to start. Hopefully I manage to figure this out.

peAk

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Re: Question about tracing circuits
« Reply #3 on: May 06, 2021, 10:27:08 AM »
I've done a fair bit of tracing in my day. I usually start by removing the PCB from the enclosure and photographing both sides of the board. Then composite the two images in Photoshop (or whatever) so you can see both sides at once. Make sure you keep the same distance to the board with the camera to make lining it up easier, but it will usually require some massaging to get it lined up. Then you can see pretty much all connections (except for traces on the top that run under an IC). Then just start drawing...or in your case, verifying with the schematic.

Here's an example that is on FSB but that nobody every actually traced:


that was really cool idea!

Zerro

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Re: Question about tracing circuits
« Reply #4 on: May 06, 2021, 11:01:46 AM »
It is really ant's work. But there are ways how to make it easier. My "Two way, excluding" approach:

To simplify tracking, at first take red, blue and green (or another colors) alcohol marker-pen. Use them to track and assign along all lenght all PCB tracks which belong to ground (green color) and power (red for plus and blue for negative polarity) consoles. Carefully "paint" with those colors (or yours chosen colors) all those tracks. This will separate lines, which aren't important for circuit tracking now. Only note which circuits are powered by this, and at what pins. Pins at the upper side you can assing with those colors too, to have good orientation, where power and ground is.

Now you can see that many of tracks are out of game for now, and start from input, and track signal and details around. All tracked paths and details, you already carried to the schematics, sing with another pen, for example blue pointed line at track side and blue point for details upstairs. Take care, if you didn't left any detail out! This way will separate all tracks and details you have already carried to the schematic. After it, you will have schematic, which you must consider now, about funcionality.

If it gives a sense :@), redraw it to the nice-looking form, and do back-control of all PCB now, from schematic you made. All paths and details, you have controlled at PCB now, re-draw with red pen in your schematic. This is very usefull way, how not to forget for any track and details, which you have assigned at the first stage!

Now, do it the same way for power branches. You will get schematic for powering your "vehement", and you can again do back-control. All signs you made in pravious stages, except power lines (it will stay usefull for some future probing), you can erase now with alcohol cloth. In my praxe, when I made PCB, I always assigned power lines with colors.

That's all.
« Last Edit: May 06, 2021, 11:44:11 AM by Zerro »
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Lubdar

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Re: Question about tracing circuits
« Reply #5 on: May 13, 2021, 11:47:06 PM »
Great suggestions!
I would add that it helps to have a general idea of what the circuit is doing, sometimes this can be obtained from the manufacturer notes. If anything it helps with realizing where things are going. If the description says there is a bridged T filter in there, you should end up tracing one (ahem...)

Maybe I'm hard headed (no.. I know I am :) ) but I usually just start tracing and drawing a "schematic" at the same time using graph paper and my multimeter, usually on different parts of a page so that later on I can look at everything I've traced and see what makes sense, hoping for that Beautiful Mind cinematic realization.
 
Sometimes its not as easy to see, but most circuits use existing building blocks , so having a resource ready with the building blocks is handy too.

If anything else, designer building blocks are frequently re-used so if you can see a schematic for a previous project it helps with recognizing what an otherwise odd clustering of components and traces are supposed to be.


If anything trace and retrace. Take a break and come back to it.
(--c^.^)--c