This is an old buck DC/DC converter to be repaired without schematics.
Symptoms: no output, green LED off.
Checked all transistors; the 2N2222 was faulty; replaced with a compatible one (D438).
After the repair, I reversed engineered the board to have a schematics for the future... just in case!
This is my process:
- Take a picture of the components side; just a small area is needed.
- Take a picture of the traces side. Make sure both pictures are scaled. They must be printed on an A4 page.
- Take a transparent sheet and overlay it over the components page. Draw the components with a marker.
- Take the traces image, mirror it horizontally, overlay the transparent over the printed mirror image and draw the connections between the components.
These are the connections I drew to get the schematics from.
Reverse engineer the board and make a schematics. That's the tedious part!
Conclusions:
With a schematics, I would have checked if the TL chip had power... (pin 12).
Happy repair!