Roland Huisman
Veteran Member
Hi Tom,
In my experience ALL TTL chips can break down, not just the 7474 for example. The 7474 and 7440 are used in huge amounts in these machines. So statistically you will find more of these defective. But there are chips like early ti and some other brands which have more problems. I have bad experience with Sprague chips as well... The quality of later generation TTL chips is way better. A SN7400 from 1969 can be questionable, but a SN7400 from 1980 will be very stable in my experience. I have had brand new 'old stock' 7440 chips from the seventies which I used to restore my PDP8/L. These ran for about 15 minutes and broke down again. No external cause, I replaced it with a newer model and the machine still runs fine.
In my experience the amount of broken TTL chips depends hugely on the quality of storage. Moisture and freezing cold seems to be a deadly combination.
Regards, Roland
In my experience ALL TTL chips can break down, not just the 7474 for example. The 7474 and 7440 are used in huge amounts in these machines. So statistically you will find more of these defective. But there are chips like early ti and some other brands which have more problems. I have bad experience with Sprague chips as well... The quality of later generation TTL chips is way better. A SN7400 from 1969 can be questionable, but a SN7400 from 1980 will be very stable in my experience. I have had brand new 'old stock' 7440 chips from the seventies which I used to restore my PDP8/L. These ran for about 15 minutes and broke down again. No external cause, I replaced it with a newer model and the machine still runs fine.
In my experience the amount of broken TTL chips depends hugely on the quality of storage. Moisture and freezing cold seems to be a deadly combination.
Regards, Roland