Author Topic: 74 series.....what If you need to replace a non-LS ?  (Read 3844 times)

level42

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74 series.....what If you need to replace a non-LS ?
« on: June 08, 2015, 06:32:16 PM »
So....The 74 series of chips started off with just that typenummer.

Later came LS versions which uses about 10x less power and should be compatible with the regular 74 chips BUT sometimes I still find non LS types on boards (like Galaxian). Sometimes these were swapped in later, and the documents say it should be LS, but some chips seem to be Non-LS on purpose, maybe for speed or maybe for fan-out properties.....

But.....non LS chips have been long out of production and hard to get. Is there a modern equivalent series that is 100% compatible with the original 74 range ?

speleo_de

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Re: 74 series.....what If you need to replace a non-LS ?
« Reply #1 on: June 08, 2015, 07:41:02 PM »
In general, a 74LSxx or 74HCTxx - if they exist - can replace a 74xx.

Still....
  • In some cases the 74LSxx equivalent is uncommon, e.g. for 7406 or 7407 which are open collector drivers, but here the 74xx equivalent is still widely available.
  • In some other cases the fanout (out driving capability of attached inputs) of the 74xx is higher.

What type are you speaking about? I have quite a collection of 74xx types.

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Re: 74 series.....what If you need to replace a non-LS ?
« Reply #2 on: June 08, 2015, 10:10:43 PM »
7404 (6E) and 7420 (3C) on the Galaxian PCB.

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Re: 74 series.....what If you need to replace a non-LS ?
« Reply #3 on: June 08, 2015, 10:20:47 PM »
Had a glance at the schematics and it doesn't look like these two drive particularly large loads so fan out doesn't seem to be the (an) issue....

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Re: 74 series.....what If you need to replace a non-LS ?
« Reply #4 on: June 08, 2015, 10:24:02 PM »
....
« Last Edit: June 08, 2015, 10:34:59 PM by Level42 »

speleo_de

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Re: 74 series.....what If you need to replace a non-LS ?
« Reply #5 on: June 09, 2015, 12:18:39 AM »
Well, the 04 and 20 should be easily available as LS or HCT type.