74 series IC substitution.

I am repairing some gear that uses 74F series IC's, does anyone know if I can substitute 74HC instead? the "fast" series chips are a little hard to find.

that will obviously depend on application.. :?:

This will give you the information you need:

http://www.interfacebus.com/Logic_Design_Top.html

Good luck.

Mach

Hi Steve

this RoHS thing is really gonna hurt eventually
so many of the favourite ICs will disappear

The 74F is probably TTL levels, the HC is CMOS, which means it is faster, and probably goes all the way to 5 volts instead of 3 or 4 like the TTL.

So if speed and level are not a concern, you might get away with a swap. You can add a buffer to the HC stuff if driving a heavy load.

In the past I repaired a lot of boards that used TTL chips. In house stuff to DEC 11/ 33 and 11/44 boards and other stuff.

Often the TTL type can matter. A good design should allow a chip that meets the paper spec to drop in: However often that was not the case.

If an F was in there there might have been a reason.

Brand can make a difference for F stuff the fairchild was good.

Some repairs needed the same brand.

What F chip brand and number and what kind of circuit? Clock rate and what it is driving (number of gates,fanout)|?

Thanks for all the replies, I haven't been able to log on for some reason for about 5 days... I am looking at the schematic to figure out if the CMOS will drive the other chips around it, but the schematic is not too clear so I will trace out the board tracks. Perhaps a 74 HCT will do.

Hey Kev, I have been on tour in the US for 16 months, so I missed out on some things, I am noticing lots of boxes in Jaycar marked "RoHS compliant", what is it all about? Why will it make chips disappear?

Restriction of Hazardous Substances.

A new European Union directive that bans the use of some hazardous elements in products, such als lead, which was an integral compound in low-melt solder, and Berillium, which was used in cladding the IC pins etc.

Now that they are no longer allowed in the EU, all the technology must change worldwide for firstly the world can not sustain two technologies for the same purpose, one for EU territories and one for the non-EU territories, and secondly the new requirements mean higher melting temperatures for the new lead-free solder, which consequently mean a totally new semiconductor and passive conductor manufacturing technology so that the products can bear higher temperatures during production, which also means some components will be inevitaby obsolete as their current sales figures can no longer justify the redesign/reproduction costs.

And all sorts of stuff...

Mach

Well, I guess it's time to get out of the vintage synth repair game, it's hard enough now to get some of the components in the old Japanese machines....

Look for pallets of stuff to appear at your local surplus.
Companies would rather throw out non rohs than get it mixed up, and then a fine or dropped product.

We have another pallet of stuff that is getting trashed.
Thousands of bucks worth of IC's, caps, management does not have the time to F with it, so out it goes.
And were a small company, 25 people, imagine what the big boys are throwing out? :shock:

:shock: :shock: :shock: :shock:

Please don't let that lot go to the dumpster! I'm heading out of town early tomorrow or I'd help dispose of it. Damn.

A P

Don't worry, Richard, down at HSC, will be glad to sell you that stuff.
:twisted:
For an inflated price, of course.
:evil:

I think you can sub AS, AHCT or ALS for F in TTL. Propagation speed is slightly less on ALS at 4ns (F is 3ns). Power is less on ALS than F. P speed on AS is the same but power is about twice F. AHCT has a slightly slower P at 4ns but the power is less than 1/10. Might have issues with logic levels though.

Here is a chart:

http://www.interfacebus.com/Speed-Power_Chart.html

[quote author="burdij"]I think you can sub AS, AHCT or ALS for F in TTL. Propagation speed is slightly less on ALS at 4ns (F is 3ns). Power is less on ALS than F. P speed on AS is the same but power is about twice F. AHCT has a slightly slower P at 4ns but the power is less than 1/10. Might have issues with logic levels though.

Here is a chart:

http://www.interfacebus.com/Speed-Power_Chart.html[/quote]

Thanks for that info, I think I will try an HCT and see how it goes, I think RS or Farnell may still have F series chips also if the HCT is too slow or doesn't have enough fan-out.

[quote author="Steve Jones"]Thanks for that info, I think I will try an HCT and see how it goes, I think RS or Farnell may still have F series chips also if the HCT is too slow or doesn't have enough fan-out.[/quote]

I have just received the latest Farnell catalogue today and some 74F series are still available, some of which are RoHS compliant and most of them are not, and quite a few of them are "limited stock -RoHS replacement available".

So you better move before things change. Pages 1:47 and 1:48.

RS doesn't do any 74F series apart from a few: F00, F04, F06, F07, F08, F14, F38, F74, F244, F245, F257, F269, F393 and F541. Some of them are DIP, some of them are SOIC, some of them are both. Page 2-1189.

You can check the availability online.

I hope you find what you're looking for.

Mach