Re: Where to start on Missile Command PCB repair

Ok not to keep getting off topic, but as this is related to the Missile
Command repair, I'm going to ask. When I look for 74191 I can't find
anything on Digikey, etc, but when I search for 74HC191 it comes up, is
that the same thing?

On Fri, Nov 1, 2013 at 8:42 AM, <solarfox@triluminary.net> wrote:

> On Fri, 1 Nov 2013 00:35:07 -0400, you wrote:
>
> >So I can generally replace a 7404 with a 74LS04 without any problems?
>
> *Normally*, yes, but there *are* cases where you can run into problems. The
> switching speed of 74LS-series parts isn't *quite* identical to standard
> 7400-series; the propagation delays of a 7404 vs. a 74LS04, for example:
>
> -------- 7404 -------- ------- 74LS04 -------
> tPLH 12ns (typ) 22ns (max) 9ns (typ) 15ns (max)
> tPHL 8ns (typ) 15ns (max) 10ns (typ) 15ns (max)
>
> (Source: a very dog-eared and well-used copy of "The TTL Data Book, vol.2",
> Texas Instruments, 1985)
>
> The difference is, admittedly, pretty small, but it can add up when you've
> got signals flowing through a bunch of different gates, or when you've got
> a more complex chip (such as the 74191). So, depending on the circuit in
> question, there's a small (but non-zero) chance that you *could* end up
> with a "race" condition by swapping a 74LS part into a circuit full of
> 7400-series chips.
> --------------------------------------------------------------------------
> "I thought I told you to look after him!"
>
> "He'll be all right; he's a Time Lord."
>
> "That's just what they're _called_; it doesn't mean he actually knows what
> he's _doing!_"
> --------------------------------------------------------------------------
> solarfox@triluminary.net (Gary Akins jr.)
> --------------------------------------------------------------------------
>
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Received on Fri Nov 1 08:51:45 2013