Tracing out the schematic of a vintage effect is not all that hard to do and has many of the elements of a detecting job. It's always interesting to figure out how an old, unusual circuit works; it may be an effect saver if you have something unusual that you can't find a schematic for that is broken. This process works well with single sided boards, poorly with double sided boards.

The process is pretty simple. You'll need:

• Clear laser printer/copier sheets for making overhead projection prints

• Two or three colors of permanent marker - "Sharpie" is one brand that works

• About an hour of uninterrupted time

• Some background in electronics, schematics and circuits

• Masking or clear office tape.

Trim a portion of a sheet of the film so it is slightly larger than the circuit board. Use the tape to affix it to the board, copper trace side, so the tape does not obscure any of the circuit. The component leads and solder joints will hold the film slightly off the board. This will not be a serious problem. Use a marker (I use black) to mark the position of every soldered component lead pad or I/O pad where it comes through the board. Use a different color ( I use green) to trace out the copper wiring traces from pad to pad.

Work carefully and methodically until the whole copper pattern is traced. Mark this piece of film "Bottom" Remove the film from the bottom of the board, and trim a second piece of clear film to the size of the fist. Tape this second piece of film to the side of the "bottom" film that you did not mark on. Turn the sandwich so the new "top" piece of film is up, and lay it on an unmarked piece of paper. You can now see the copper pattern you traced as though you could see through the printed circuit board material. Using a third color ( I use blue) draw the parts in on the "top" film, referring to the real board and noting component values as you go. The pad markings which you can see from the "bottom" tracing allow you to relate the component leads to one another easily.

Mark the "top" layer appropriately. Now, you have what amounts to a clear circuit board, and you can pretty much just draw the circuit out, referring to the real board with perhaps an ohmmeter when you get stuck. Most older effects are not complicated enough to be any real problem when you get this far.

 Method 2 - High Tech

The key to being able to trace something easily is that you have to be able to see relatively clearly where each copper trace goes from each component lead that is soldered to it. That's the whole point of the clear mylar tracing procedure outlined in Method 1 - you make a clear tracing of the bottom and top and can then relate the two together without the obscuring board in your way.

It happens that modern scanners can help. When I first used a scanner, I presumed that the scanning heads were focussed narrowly on just the plane of the glass. Not so. A quirk of scanner optics is that the depth of focus for a scanner is larger, maybe as much as an inch away from the glass. If you put a pcb on the glass surface of a scanner, the scan it makes is in focus. Not only that, if you turn the board over so the component side is on the glass, the board and components are still probably in focus.

This makes it easy. Scan the copper traces side, scan the component side, and print one of each to a clear plastic film sheet. You should be able to then trace things out pretty easily.