Re: Where to start on Missile Command PCB repair

From: Grant Thienemann <grant.thienemann_at_gmail.com>
Date: Fri Nov 01 2013 - 09:17:51 EDT

Hey Rodger,

Thank you for the information. I'm looking at wikipedia now about the 74XX
series chips, which would be the default standard when looking to replace a
7400, or 7404 etc, would that be HTC?

Thanks
Grant

On Fri, Nov 1, 2013 at 9:08 AM, Rodger Boots <rlboots2@gmail.com> wrote:

> Close. HCT is closer. Either should work.
> On Nov 1, 2013 7:52 AM, "Grant Thienemann" <grant.thienemann@gmail.com>
> wrote:
>
>> 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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>>> chris@westnet.com
>>>
>>
>>

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Received on Fri Nov 1 09:17:56 2013

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