Re: Galaga - problems setting Rank D

Thanks for the info. I wasn't going to try it, was just more curious if it
could be done. And yes, those chips are very cheap. Got a six pack of them
locally for $2.50, tho I ended up not needing them.

Rodney

On Thu, Nov 4, 2010 at 11:46 PM, <solarfox@triluminary.net> wrote:

> On Wed, 3 Nov 2010 20:21:17 -0400, you wrote:
>
> >Yes. I checked both of the SIP packages for the dip switches and they
> >measure 4.7K ohms.
> >
> >I'm thinking it's probably the 151 chip at 4K is bad. I'll pickup some
> >tomorrow and see if that does the trick.
> >
> >Question, is it possible to piggyback a TTL chip like the 74LS151 on top
> of
> >another one to see if it's bad?
>
> I would not recommend that, no. Among other things, the 74LS151 is
> *not* an open-collector output part, so the output pins are always trying
> to drive high or low via a pair of transistors in a totem-pole arrangement
> -- and if one of your suspect chip's output pins tries to drive low while
> the test chip is trying to drive the same pin high (or vice-versa), the
> result is a direct VCC-to-GND short through the output transistors, which
> might actually damage the piggybacked test part.
>
> The 74LS151 isn't exactly a rare or expensive chip, so if you think
> the
> chip is suspect, I'd just replace it.
>
>
> -----------------------------------------------------------------------------
> "I'll tell you what's eating me, "Beach Blanket Bimbo Fiesta" boy; I'm
> turning
> thirty in three weeks."
>
> "Ah, the fiery ritual of Carousel. Perhaps you'll be renewed."
>
> "Yeah, we'll see if you're laughing in six months when *your* palm is
> blinking red."
>
> -----------------------------------------------------------------------------
> solarfox@removethis.triluminary.net (Gary Akins
> jr.)
>
> -----------------------------------------------------------------------------
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Received on Fri Nov 5 10:03:52 2010