8 Mar
2008
8 Mar
'08
10:15 a.m.
Pete Turnbull, quoting me:
Thanks for the tip. 6821 or 6820 goes on my mental wish list.
Philip.
When I was 13
(1980. Ouch!) I was given a PET for my birthday. A few
years later I blew up an output buffer in one of the 6520s trying to
use the Cassette 2 motor output as a controlled power supply. We
connected one of those two-tone doobells that uses the back emf from
the "ding" solenoid when you open the switch to sound the "dong".
Said back emf killed the output buffer on that pin of the 6520. It
managed to do so without any noticeable damage to the intervening
circuitry, too!
Common problem -- 6520s are fragile. For that reason, it was common, at
least here, to replace them with Motorola MC6821s, which was a later
version of the MC6820, which is just the same as the MCS6520. Lots of
the PETs at the college where I worked in the early 80s had Motorola
replacements because the 6821 seems to be more robust than the 6520.
So replacing the missing or damaged 6520 with a Motorola MC6821, which
should be much easier to find, even has a degree of authenticity :-)