Re: Need help with an Atari Pong board

On Sat, 19 Jul 2008 12:39:20 -0700, you wrote:

>I replaced the 7493 IC's with new 74L93 IC's (Not 74LS93).

        I think this is your problem. The 74L93 is too slow for this circuit;
F8 is being clocked at 7.159MHz, and according to my TTL Databook, the "L"
version of the 7493 has a maximum fCount frequency of 3MHz. By comparison,
both the base 7493 part and the 74LS93 are rated up to 16MHz on the CLKB
input. (32MHz on CLKA, so if QA is tied back to CLKB then the whole 4-bit
count can be run at 32MHz; they specify them separately because if you were
trying to use the CLKB-driven section only, to make a 3-bit counter, you
could only clock it at 16MHz.)

        In general, you have to be very careful about substituting an
"L"-family part for a standard TTL, or even an LS part; 74Lxx logic is
*much* slower, and it has much lower current-output capability.

        Put a proper 7493 in there, and see if that doesn't produce more
positive results. :)

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solarfox@removethis.triluminary.net (Gary Akins jr.)
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Received on Sat Jul 19 17:03:28 2008