On 05/03/2013 7:32 PM, Jose Luiz Martins wrote:
Hi !
Have you guys experience problems using 74LSXX instead of 74XX in address bus?
I'm trying to troubleshoot one Taito Moon Cresta board for months, and could not find the problem.
I solve the garbage on the screen changing one 7408 at Data Line A5,A6 and A7 but now I have the screen filled with Zeroes and Ones.
I was noticed by a friend that the 2114 is very speed sensitive, but I cant believe the 74LS08 is the guilty.
I'm asking you guys because I don't have any good 7408 IC, I'll have to order it from USA and wait about 30 days to arrive.
Thanks As I've found in repairing games the problem with using 74LSXX in place of 74XX devices is the drive current of the 74LSXX series is 1/10th (more or less) of the original 74XX. So if you find the LS device is only driving one standard TTL gate that is usually OK, however if driving 2 or 3 it can be marginal, and 4+ is normally pointless. So try a 74HCT08 if available - High Speed CMOS TTL compatable outputs, I believe this is closer to the 74XX family.
If you have some 74XX data books they do go into drive capabilities of the various families (often called fan-out too). I'm also certain there are searchable info on this topic. John :-#)# _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ttl.arcadetech.org/TTL/Test_Equipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/