Is it Ok to replace a 74HCT series logic IC with a 74F series?

Vypr · 19 December 2021, 21:24

I discovered my Amiga 3000 daughterboard was not detecting any card sinserted into it.

I removed the caps and checked them and they were out of spec (220uF measuring as 280-290uF) so I've ordered replacements.
Just for completeness sake I removed the two logic chips and ran them through my Retro Chip Tester (Absolutely love this thing)
U601 - A 7407 is fine but U600 (74HCT32) failed.
I don;t have a replacement 74HCT32 to hand but I do have a 74F32 in my spares box. Would it work if i use this?

Daedalus · 19 December 2021, 23:03

It's probably fine - F logic will be much faster so if the signals are a bit noisy or have slow slew rates you might get multiple false switching, but if things are like that you're probably gonna have other issues too.

Threshold- and supply voltage-wise they're compatible. It's say it should work fine.

Vypr · 20 December 2021, 11:28

Cheers, I was pouring though the datasheets for it, didn't want to put another order into Farnell after submitting the one ofr the replacement caps and have to pay for double shipping.

19 December 2021, 21:24	#1
Vypr Registered User Join Date: Dec 2016 Location: East Kilbride, Scotland Posts: 451	Is it Ok to replace a 74HCT series logic IC with a 74F series? I discovered my Amiga 3000 daughterboard was not detecting any card sinserted into it. I removed the caps and checked them and they were out of spec (220uF measuring as 280-290uF) so I've ordered replacements. Just for completeness sake I removed the two logic chips and ran them through my Retro Chip Tester (Absolutely love this thing) U601 - A 7407 is fine but U600 (74HCT32) failed. I don;t have a replacement 74HCT32 to hand but I do have a 74F32 in my spares box. Would it work if i use this?

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19 December 2021, 23:03	#2
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,348	It's probably fine - F logic will be much faster so if the signals are a bit noisy or have slow slew rates you might get multiple false switching, but if things are like that you're probably gonna have other issues too. Threshold- and supply voltage-wise they're compatible. It's say it should work fine.

20 December 2021, 11:28	#3
Vypr Registered User Join Date: Dec 2016 Location: East Kilbride, Scotland Posts: 451	Cheers, I was pouring though the datasheets for it, didn't want to put another order into Farnell after submitting the one ofr the replacement caps and have to pay for double shipping.

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