How I used 3D CAD modeling to find the problem with a circuit

Thread Starter


Joined Mar 1, 2017
First of all, I'm a complete electronics novice so any tool that helps me is considered a bonus.

If you spot any other obvious errors on this board I would really appreciate hearing from you!

I was finally able to get the USB port working. I am now getting 5v at the positive terminal of the USB port. But, only 120mA of current which I think is too low. I'm thinking the 75k resistor is resisting too much current. Could be wrong of course.

In another thread, link here -
I've been trying to diagnose the problem with a USB power adapter. It's a very basic circuit and this "might" be of more interest to those not advanced in electronics of course, but for those of us getting started this just might be of some value.

I was able to use CAD modeling to figure out why the USB outlet of this device never work at all. I didn't get the answers needed so I kept digging and decided to model the circuit so I could see all components, all traces and basically BOTH sides of the board at the same time. I first tried doing something similar in KiCAD...but I just couldn't get the clarity I needed.

What I found was that the designer had made a massive mistake designing the board and designed it with the IC chip connections mirrored backwards so that the remedy was soldering the chip on the BACK side of the board.

Using the clarity of these images (in the CAD system I can rotate them in infinite angles and vary the opacity of any part of the model) and using the chip manufacturers Pin out diagrams, I was able to clearly determine that the PCB layout for the chip was mirrored and therefore reveresed from what it should have been.

Testing all that, I installed a new MC34063A chip in the BACK of the PCB so that the pins now correspond to the manufacturers specifications.
It worked. The port now is getting proper voltage but current is low. (Although the current is low probably because of an improper resistor which I'm investigating now).

Anyway, for anyone interested who might also use CAD design, I found a way to use it to help me. Of course, using a PCB package such as KiCAD or any of the other PCB design packages is another way. I just was not able to resolve the issue that way but I was able to do so using CAD.

I'll admit up front that I'm a CAD freak and it's a hobby that I enjoy and I'm just happy to have found a way to use PCB design and 3D modeling CAD in this hobby (electronics)

Hope you enjoy and find it interesting in some way :)

First, here is an image of the actual circuit board.....notice the chip should be flipped on the central axis parallel to the pins.

And here are some of the 3D CAD models I drew to help isolate the problem (Note: obviously you experts probably could have seen it easily....but noone came forward with that in the other thread)
In the graphic below, I can CLEARLY follow the circuit and see what goes where. It was actually this one that led me to the flipped IC problem.
I set the Positive (12v+ power tracks) to RED) and the Negative (Ground tracks) to DARK GREEN.
As you can see in this next graphic, the IC chip pins 8 and 1 are at the top. Going down the right side of the chip you can see that 12v+ is going to pin 3
Wrong...according to the manufacturer Vcc or 12v power IN must go to the pin on the opposite side.....Pin 6. VOILA !!
After checking the other pins against the manufacturers pin out I could see what happened to this circuit.

A bottom view of the 3D modeled board with all pins visible
Ok...feel free to bust my chops....but I had fun doing it and DID find the problem regardless :)
As I get more acquainted with KiCAD I'll probably find a way to do this in KiCAD....eventually.
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