AT&T 4425 (Teletype 56D) repair
ard at p850ug1.demon.co.uk
Wed Apr 6 23:25:54 CDT 2016
> The "SL0227 / 404780" part appears to be a Zilog Z80 CPU of some kind,
The '404780' number looks a bit like a Teletype part number...
IIRC the Z80 has very odd positions for the power and ground pins, you
should be able to verify that it is a Z80 from that. Then stick a 'scope
or counter on the clock input pin to see how fast it is being driven, that
will tell you what type (plain, A, B, H) is needed.
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