Repair methods (was Cromemco 3101/Beehive B150 score)

[Andy Holt]

Tony wrote:
> I haev never understood how you can understand digitial electronics
> properly and not understand analogue electronics. I certaimly couldn't
> understnad digital stuff until I understood things like transmision
> lines, termination, etc.
You can understand it well enough to use for many practical purposes by just
knowing a few "rules of thumb"*. A better, but still not necessarily
detailed, understanding of the analogue background can help considerably in
some of the more tricky situations - especially if you are
"stretching"/abusing the "rules". Too detailed a consideration of the
background can actually get in the way [the best example I have of this is
the realisation that one has much more tolerance in termination than
analogue theorists tend to expect - half or double the normal termination
resistance does produce reflections ... but they are small enough that
digital inputs will ignore them even though they would be a disaster in,
say, an audio or RF amplifier].

* eg, "fanout";
 "use lots of decoupling - then add some more";
 "keep connections short - and be very cautious of long adjacent runs";
 "If mixing LSTTL and CMOS don't connect both types of input to the same
output";
 and so on.

Andy