Re: Error trying to update powerpc64 Jessie machine.
Yes, as announced by DSA, the powerpc buildds have been shut down:
Tears in all directions. At least from those of us that love our risc
We are currently in the process to properly move powerpc to Debian
Ports. In the meantime, you can either reinstall your machine with
Debian ppc64 from Debian Ports  or wait until the transition is
Jessie on powerpc is no longer being updated and supported. You
will have to switch to Debian unstable.
It is perfectly possible to install the last supported 64-bit release
and then dist-upgrade to sid and everything seems to run just fine. I am
having no troubles ( nothing fascinating other than some datatype
weirdness ) on a PowerMac G5 :
nix$ uname -a
Linux nix 4.17.2-genunix #1 SMP Fri Jun 22 23:42:51 GMT 2018 ppc64 GNU/Linux
However I really should yank the disks out and try the latest installer
with grub2. Just for testing.
ps: the next big *thing* will be RISC-V which I am also interested in