Boffin1:
But replacing a fauly 4000 chip with a micro is a bit expensive ?
Thanks for the birthday wishes 
- yes it would be expensive, but i was thinking more along the lines of "uh oh, this circuit requires a whatever logic gate" - you don't have one but if there's a library
full of emulated logic chips, while you're waiting for the shop to open or ebay to send the chip, why not program a small unused attiny to do the job for you? until you
get one...
Esp if you're learning about logic chips and don't actually want to buy any....