After a brief detour playing with AI-powered image generators, I returned to the challenge of deciphering the workings of voltage step-down converter (a.k.a. buck converter) modules I bought off Amazon(*), built around a chip I can only identify by its marking "AELH". Not only is the identity of the chip is still a mystery for now, tracing through the surrounding circuitry is really hard due to the fact whoever laid out this circuit board was very efficient at packing everything into a small space and left very little room for me to tease out circuit traces.

It's possible to see a difference between areas with and without copper, but it's not a very clear difference. I tried polarizing filters but they didn't help in this case. I also tried playing with contrast settings in a photo editor, which has partial success but still not clear enough.

The difference is much more visible on the back side (flipped here so all the vias line up between these two pictures) where it lacks shadows cast by various components. One defining characteristic of copper traces on a circuit board is that it is completely opaque, relative to partially translucent areas where we have just green solder mask over circuit board substrate without copper. Because the backside is generously covered with copper, shining light from the back won't help me see traces on the front because the light will be blocked.

So I thought I would try shining light into the circuit board substrate from the edges. Looking in my pile of parts for a sharply focused light source, I dug up my pack of red LEDs with a tight beam pattern. (*) These were intended for use as "laser" pointers while being much cheaper than real lasers, and I bought them for my Lissajous curve project.

The results showed promise but clearly not enough. The advantage of these modules is their tight focus, not their power output. Once I shine that light into a circuit board, their light energy scattered as expected. Unfortunately it just didn't pump in enough light to bring out much detail. I turned off all the room lights and turned up camera sensitivity, but it was not enough.

If raw power is more important than precise direction, maybe all I need is a bright LED. The easiest one to try is the "flashlight" feature on my phone sitting close by. I already had the AELH buck converter module in my Stickvise (*), sitting on a breadboard to bring it up to the right height for my camera lens. By coincidence, this was also the right height to line it up with my phone LED making the experiment easy.

We have a winner! The white LED set the circuit board substrate aglow, showing all copper traces as clearly visible dark paths. The effect is most pronounced on the left side and contrast quickly falls off towards the right, but for this module I only needed help on the left. If I need to apply this technique on a larger circuit board in the future I will probably need to build a rig to shine white LEDs from multiple directions, but for today my phone LED illumination was enough to trace through this circuit and draw up a schematic.

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.