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I have not read anywhere about the possibility of substituting those chips. I haven't had occasion to test it myself either.
Just going by the hardware of the period, I'd probably guess that the HCT won't work. LS *might* work, but since the voltages are lower, it also might not.
I would try to stick with the original part, if possible. They are common chips and should still be available from various suppliers.
Quoted from Doggy:When the poster stated the original chip was a 7402for Z8 the original chip was actually was a 7404.
No, different chips have different logic in them and perform different functions.
A 7402 is not functionally equivalent to a 7404. Here are the logical pinout diagrams for three different chips:
pasted_image (resized).png
LS, HC, HCT variants are different series of those chips which have different properties (TTL vs CMOS and/or different voltage thresholds), but have the same logical functionality.
So, if you put a 7402 in place of a 7404, no, it will not work since the pinouts are different and the chip logic is different.
Quoted from Cheddar:This is driving me nuts. I thought I saw a cross reference of sys 1 ics and modern replacements last week but I can't find it again
There's an extensive one for system 80 MPUs. Is that the one you're thinking of?
Quoted from Doggy:Below is a copy of the post:
Replacement ic chips
MPU board: Easiest one -- 7448 can be replaced with 74LS48 ... both of which are obsolete.
Z1 original 4528, no alternate and obsolete.
Z2 original 7474 but can easily use 74LS74 or 74HCT74.
Z3 cannot use a 74HC04 or 74HCT04, these have "high impedance inputs" and won't work properly in an oscillator circuit. Original is a 7404. You should be able to use a 74LS04 or 74F04 but I have not tried them, best bet would be 74LS04.
Z4 original 4081, no alternate but still an actively produced component.
Z7 Original 74LS04. Can use 74LS04 or 74HCT04
Z8 Original 7402. Can use 74LS02 or 74HCT02
Z9 Original 7400. Can use 74LS00 or 74HCT00
Z10 Original 74LS05. No alternate but still actively produced. Can Probably get by with a 74LS00 or 74HCT00 but I have not tried this. Changing to a 74LS00 or 74HCT00 will defeat ability to test board using QuickScan80 (which I am supposed to be working on Version 3 right now).
Z11 & Z12 Original 7404 in switch matrix & few other places. Only has to sink ~2mA so can probably be replaced with 74LS04 but might result in noisy switching.
Z13 & Z14 Original 7400. In switch matrix. Can probably replace with 74LS00. Don't think I would go to 74HCT00 here as this may also result in noisy switching.
Z16 original 7404 but can be replaced with 74LS04 or 74HCT04.
Z17, Z24 and Z26 original 7404. Digit Strobes. Should be able to get by with 74LS04.
Z18, Z20, Z22 original 74175. Can use 74LS175 or 74HCT175
Z15 original 7432. Can use 74LS32 or 74HCT32.
Z27 original 7404. Can use 74LS04 or 74HCT0ppp
Z28 original 74LS139. Can use 74HCT139
Z29 and Z30 original 7416. Can use 7416 or 7406.
Z31 original 7408. Should be able to go 74LS08. 74HCT08 would work but not a good board to board driver.
Z32 original 7417. Can use 7417 or 7407.
Z33 original 74154. Can also use 74LS154 or 74HCT154 -- all of which are obsolete.
Z34 and Z35 original 7404. Can also use 74LS04. 74HCT04 would also work but not a good board to board driver.
On driver board: All 74175s can be replaced with 74LS175 or 74HCT175.
Z13 original 7404 can be replaced with 74LS04. 74HCT04 would also work but not a good board to board driver
That's for system 80 MPUs, not System 1 MPUs.
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