Re: Galaga - problems setting Rank D

From: <>
Date: Thu Nov 04 2010 - 23:46:26 EDT

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."
----------------------------------------------------------------------------- (Gary Akins jr.)
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Received on Thu Nov 4 23:46:37 2010

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