nid your HELP ASAP!! 24 secs shot clock

[ertiexd125]

https://www.electro-tech-online.com/attachments/24s-jpg.4492/

the diagram is in the link.. our problem is when the digit 4 counts down and reaches 0 the digit 2 also become 0. to be more specific if the countdown reaches 20 the next output should be 19 but its not its 00.. where must be the problem??

 

[mneary]

When the first 74ls192 reaches 0 the second 74ls192 is at the very same time trying to change from 0 to 1. The second action does not happen fast enough and the 4078 sees both 0's for a moment. It passes this through the 1k to the reset inputs.

Solution is to put a latch such as 74ls74 after the 4078 so it waits for the next clock before making a final reset.