I purchased and reverse engineered a cheap eBay ultrasonic power supply, to see if it held any value for the hobbyist.
This first post explains the process of reverse engineering the (or any) board.
A subsequent post will discuss the specifics of this board.
NB: Can anyone tell me what R4 (1 ohm, 5 watt) does in the schematic below?
How to reverse engineer a simple PCB
Dave Jones posted a great video (from his blog) showing how to reverse engineer a PCB. He prints and overlays transparencies of the board top and bottom, so that he can visually align the traces with the components.
I did essentially the same thing, but within a paint program - eliminating the need for physical copies. This has some advantages over his method (zoom, annotation, and contrast adjustment), but some disadvantages as well (small visual aperture).
Step 1: Take a picture of the top and bottom of the PCB
Step 2 Flip and flood
Flip the trace image left-for-right, and flood-fill the copper traces with a high-contrast color. Use the pen/brush tool to touch up areas that didn't fill properly (ie - the shiny, reflective bit in the image above).
Step 3: Make a sandwich image
Compose a 3-layer image with the components image on top, the traces in the middle, and a white bottom layer. Set the bottom (white) layer opacity to 100%, and adjust the opacity of the trace and component layers to give a nice X-ray view of the board.
(This will be specific to your eye sensitivity and the characteristics of your display, so adjust to taste. For my setup, the best settings seem to be White: 100%, Trace 100%, Components: 78%.)
Rotate and adjust the trace layer so that the holes in the trace layer line up with the components.
Step 4: Zoom and annotate
The image can be zoomed and annotated as needed. Also, sections and components can be erased once deciphered. (I found this particularly useful - certain sections are "distracting", and blocking them helps me concentrate on other sections.)
The results: a shiny, new annotated schematic, ready for the surgeon's table:
A high-resolution version of this (pdf and svg) will be available on GitHub presently, as well as the KiCad schematic.
Discussion of this specific circuit will be in a subsequent log.