Re: 74SC240 cross or datasheet?

On Tue, 18 Nov 2008 11:05:17 -0800 (PST), you wrote:

>I'm back to looking at my Kozmik Krooz'r. The joystick doesn't work and
>one thing I noticed is someone replaced the 74SC240 with a 74LS240.
>
>Does anyone know if the LS240 or HCT240 are drop in replacements?
>Does anyone have a data sheet for the SC240? I've looked around the web
>& RGVAC and couldn't find a link to one.

        The 74SC00 series was the precursor to the 74HC00 series, so you might
try dropping a 74HC240 in there and see how it goes...

        Interestingly enough, while searching for info on the 74SC240, I came
across a link to the patent document which describes the operation of this
joystick circuit in detail: http://patentpdf.net/US4685678.pdf . The
description specifically indicates that either a 74SC240 *or* a 74LS240
*should* work in this circuit, and from looking at the Kosmik Krooz'r
schematics, I can't see any obvious reason to think otherwise.

        Suggestions:

        (1) Scope the output of the two oscillator sections, at pin 10 of the
MC14040 chips @ 3B and 4A; see if the oscillators are running, and whether
their frequencies change when you move the stick around.

        (2) Scope the outputs of the MC14040 chips, at pin 4; the output should
be 1/64 of the input frequencies at pin 10.

        (3) Scope the outputs of the 74393 counters to make sure they're
actually counting pulses.

        If the 74393s or MC14040s arent running, make sure the CLR* line (the
signal from pin 5 of J1) isn't stuck low.

        
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solarfox@removethis.triluminary.net (Gary Akins jr.)
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Received on Tue Nov 18 20:19:02 2008