The Commodore TED-machines C16 and Plus 4 come with the MOS 8501 MPU, which is generally compatible to the MOS 6510 (which is in turn a variant of the 6502), but differs in the pin-out. Another property of this chip is that is known to fail as it ages and that it is quite rare and expensive to replace. What to do? Maybe building an adapter? This is exactly what Adrian Black does in these videos.
As a minor drawback, the resulting CPU is missing an I/O-pin used for loading and saving programs, which may be addressed by a Kernel hack. (However, this isn’t addressing fast loaders, which are still awaiting respective modifications of their own loading routines.)
The modifications are based on a blog-post by “Andy”:
Adrian Black’s video, Part 1 of 3 (3 still to come):
Part 2 (mind the links in the description):