>Unless the 'key part' is particularly obscure, once
>the basic function and pinout has been determined,
>it is usually not hard to figure out what it is
>with a bit of searching. If someone is really
>determined, they may also try de-capping it to
>establish the manufacturer - chips quite often
>have makers marks on the die.

Or the underside of the chip.

I have an HP 7475 plotter that was going to be dumped as it was faulty, and
HP wanted something like the cost of a brand new plotter to send it from new
Zealand the USA for repair. We had a second identical working one in the
workshop which one of the techs used to swap chips between them to identify
the faulty chip. Tried to get just the chip from HP but they would not play
ball. When I got it I removed the known fualty chip which had the HP chip
number on the top, and looked at the bottom. It was marked 6805, so I
grabbed a Motorola 6805 processor from some other equipment we had, plugged
it in, voila, working plotter in about 5 minutes.

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