First up is the chip under test actually faulty?

Sorry should have clarified that, yes the chip was faulty changing it bought the Space Invaders back to life. cheers Chris If you ever want to (un)subscribe yourself with TTL, you can send mail to: <Majordomo@flippers.com> with the following command in the body of your email message: (un)subscribe techtoolslist or from another email account, besides xxx@yyy.com: (un)subscribe techtoolslist xxx@yyy.com