In message , at 09:08:18 on Tue, 30 Jan
2018, Someone Somewhere remarked:
You'll know then which components were impossible to source. Feel
free to fill us in on which ones they were.

As I've said more than once it wasn't a components problem. It's that
the boards were unmanufacturable at any affordable price. They needed
redesigning for modern components

I think Spud wants to know why they couldn't use the old boards with
the *old* components.

What old boards? They would have to be made and assembled from scratch,
an unaffordable prospect for the additional radios Railtrack wanted.

So we may be getting closer - the problem was a lack of boards, not a
lack of components to put on them?
Unmanufacturable covers a range of situations.

Nothing that was manufactered is unmanufacturable - it may not be
reasonably economic to do so, or in certain cases legislation may
prevent it (lead etc) but if it was built once, it could be built again.

There are whole generations of custom-chips which aren't manufacturable
any more. Either the company which made them originally has gone out of
business/disappeared within another that's not longer in the foundry
business, or the tools and machinery required to produce a new batch
have long since been consigned to the dustbin of history.

A handful of generic chips may still be available, so you could perhaps
get a brand-new Z80 equivalent/clone processor chip to build a replica
Amstrad CPC464, but good luck getting Ferranti or SGS to make you a
fresh one of the ULAs.
--
Roland Perry