Correct; the HC is definitely a better replacement for the 40H, but I'm pretty sure that in a pinch the HCT would also work.
m ----- Original Message ----- From: "Francesco Messineo" <francesco.messi...@gmail.com> To: <m...@bitchin100.com> Sent: Wednesday, August 02, 2017 1:05 PM Subject: Re: [M100] Model 100 serial port > On Wed, Aug 2, 2017 at 6:47 PM, Mike Stein <mhs.st...@gmail.com> wrote: >> Good advice; the most likely culprit (because it's indirectly connected to >> the outside world with its static, lightning, ground loops etc.) is M35, a >> (1)4584. >> >> The only other IC would be M24, a 40H032 (which could probably be replaced >> with a 74HC(T)32). > > > 40H family is directly replaceable with 74HC family. I wouldn't use > 74HCT chips in this circuits, the TTL voltage input compatibility > isn't needed (and it doesn't do harm anyway) but switching times and > power consumption of the HCT family are slightly different from the > original 40H and the almost-identical 74HC. > > By the way, the UART chip could be the culprit too, just trace the > signal back from the DB25 until it disappears. (Or start from the UART > pin forward to the external world). > HTH > > Frank
