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  • Author Author: baldengineer
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Are you still using 7400-Series Logic, if so, where?

baldengineer

Over the past several months, I have been learning about and repairing 8-bit computer and video game systems. So far, I have worked on the VIC-20, C64, ZX-81, Apple II, and have been learning about the TI 99/A.

 

It always amazes how much of these early computer systems were built almost entirely with standard 7400-series (LS and HC) chips.

 

Occasionally, I need to replace a 7400-series chip. (I always hope it is one of those and not one of the ASICs!) While looking for modern replacements, I have noticed the trend that they are becoming more scarce. The LS-series is almost entirely gone--and with good reason. While HC and HCT continue to be somewhat available, they are usually only available in surface-mount packages.

 

That leads me to the question: Who is still using the venerable 7400-series logic chips today?

 

To me, there are three groups that might be using them:

  1. Learning. Students and hobbyist learning about digital logic
  2. New Design. Hardware that needs glue-logic. Are these using multi-gate chips or the single-gate variants?
  3. Repair. Older electronics in need of replacements. Here is where I mostly sit.

 

Do you fit into one of those categories? If not, where do you land?

 

And THEN, which chips are the must-have on-hand?

Obviously, the answer depends on how you might be using them. But, I'm curious to know how you use 7400-series chips and which ones would you keep in stock?

  • in reply to michaelkellett

    Hi Michael,

    I bet they're nice instruments too, usually no expense spared with their equipment design. Although I can't remember those two, as an end user I've encountered a fair amount of Racal test equipment, mainly because all of their subsidiaries 'ate their own dogfood' and would purchase equipment from each other if they could rather than elsewhere.. I worked for a while at one of them, although not Racal Instruments. Racal Instruments was based in my home town though, I'd walk past it on the way to school.

  • in reply to shabaz

    I like the cute little plastic holders for the vertical resistors.

    I doubt that they do any good in terms of vibration or other protection but certainly look pretty !

     

    I've got a couple of Racal instruments (mV meter and Frequency meter) - they are still working fine

    (at similar age) so I've not opened them up.

     

    MK

  • Here an electronics chain called Maplin was selling 74-series TTL right until 2018, when it closed for good! I guess people were still buying them, perhaps to repair old equipment. I think this is the oldest test instrument I own, it uses about fifteen 7400 logic chips:

    image

    It is a counter/timer.  I don't use it often (but sometimes handy). I occasionally just use it as a large stopwatch : )

    It was in bad shape when I got it (used) a couple of years ago from ebay, lots was oxidised or covered with stains, and the sockets were corroded too.

    I took it to pieces to clean it all, and replaced the BNC connectors and some of the buttons, and the large power supply electrolytic, and the display filter which was scratched up.

     

    The main fault (apart from cooked input resistors and some traces) was just bad contact with clogged-up switches (I sprayed isopropanol and then air into them all) and poor contact with one main IC (see photo below, it is the white chip at top-right in the photo, and also visible in the photo above) that was socketed (the rest of the ICs did not have sockets). I removed the socket and permanently soldered the IC, and now it works fine.

    The weird round IC in the centre of the photo is a Plessey divider chip.

    image

  • in reply to michaelkellett

      wrote:

     

    .... You could get all this into a decent micro-controller and and a (smallish) FPGA now, not sure if image or image ...

    I'm going for image.

     

    Mind blown also. What a beautiful and well-designed kit.

    It's not easy to make an appealing and functionally understandable front panel.

  • in reply to dougw

      , Dito I had a slab of plexiglass with the stainless reference bar.  My brother was a PCB layout guy and did more than A few Double Sided PCB, once even  4 layers; top signal, ground, power, and a bottom signal side. We had the boards done locally with gold fingers, and feed-through holes.

    ~~Cris

    BTW No pics as they are still packed.