tracing out schematics

It may hgave been somewhat tongue-in-cheek :-). I've done things a _lot_ more complicated than a 4 layer board and lived to tell the tale. But then I've done rather a lot of this... It's got to the stage here where for a simple board (say a PC I/O card with one known 'big chip' and some glue logic) it takes perhaps an afternoon to produce a complete, annotated, schematic. But against that, something like the HP9100B calculator took 6 _months_... However, I would always claim a schematic can be produced (direct chip-on-board being a possible exception!). And therefore if the choice is between having to draw out a schematic or not repairing the machine, the former always wins! In generaly you trace connections with a meter, not just by eye (and don't worry about scrapping off the soldermask to see which of the half-dozen traces coming out from under an IC corresponds to the one you're tracing!). So traces under components (or on middle layers of the board) don't worry me too much. But you may well have to desolder some components -- as I mentioned in the other message, you must remove anything that tests as a dead short. -tony