As a KiCad practice exercise and for a better understanding of modules I use in my projects, I wanted to trace through circuitry of this voltage step-down converter (a.k.a. buck converter) module. Unfortunately, it packed its components too tightly for me to easily see copper traces on this circuit board.

Then I figured out I could light up the circuit board substrate from the side, making all opaque copper traces clearly visible.

Now I could trace through all the paths, taking notes as I went.

I learned a new lesson about markings on surface-mount resistors. When the third character is a letter, it is an EIA-96 code and I need a decoder like this one on DigiKey to decipher their nominal resistance.

There's no room for component labels on this tightly-packed module, so I assigned my own.

And here's the KiCad schematic I generated from my tracing notes. Aside from the row of voltage pre-select resistors, it is superficially similar to the MP1584 module which is no surprise given they serve the same purpose. The most curious difference for me is the lack of a diode in this module. I had thought that was a required part of voltage conversion. Either I misunderstand or an equivalent is built in to this unidentified AELH chip.

Another surprise was the potentiometer only go up to 40k Ohms. Judging by the row of pre-select resistors, this implied the potentiometer is only be good for up to a little over 5V. If we want to go any higher, we'd need to use the pre-populated resistors for 9V or 12V, or figure out something on our own.

This KiCad learning project is publicly available on GitHub