cropduster wrote:

Scott 558T digital AM/FM tuner, bought in October of 1983
but probably built a year or two before. It doesn't remember
station presets anymore when switched off. I looked inside
briefly for a coin cell battery or large capacitor but
nothing caught my attention. How did digital electronics of
this age remember things when switched off?

I don't know anything about that Scott tuner but a lot of stuff designed
in the early 80's used these serial eeproms like an 93c46.

It's a 8 pin dip (usually) and was fairly simple to use and incorporate into
a design. Most were only a half k or 1K in size but was more than enough
to hold a table of stations or other settings.

They were used in many products including alarm panels, car radios and
various other consumer electronics that were "cutting edge".

They did not last forever. There was a lifespan to them, read cycles were
in the 100's of thousands but write cycles were in the low thousands.

There might of been a general lifespan in years too.

-bruce