74XX TTL Series questions (newbie)

Discussion in 'General Electronics Chat' started by disjaukifa, Nov 1, 2013.

  1. disjaukifa

    Thread Starter New Member

    Nov 1, 2013
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    Hey,

    New here and first let me say I have no training whatsoever in electronics, just what I have learned on my own. I collect arcade machines, have over 30, lost the exact count, but I've gotten them mostly broken and I've been very lucky and I've been able to repair a few with very little work but now I'm to the point that I'm really having to dive into PCB repair.

    I have the majority of the equipment to do so but really I have a major question about 74XX series chips that I can't seem to find the answer too. Most of the PCBs I'm working on seem to have bad 74XX series chips on them. I have these questions I would like answered.

    1st. Can you replace a 74XX with a 74LS perfectly fine since both are 10ns delay, the 74LS just uses less power.
    2nd. Can you replace a 74HXX which is 6ns with a 74ASXX,74ALSXX, or 74FXX since all three have a lower delay of 1.7ns, 4ns, and 3.4ns respectively.
    3rd. Can you replace a 74SXX which is 3ns with a 74ALSXX which is 1.7ns. I don't think you can use a 74FXX because its 3.4ns.

    I've been looking for two days now and I haven't been able to find a definite answer to these questions. I really don't want to change the characteristic of the game, which in this case is Missile Command, because I installed a wrong 74XX series IC somewhere on the PCB.

    Thanks
    Grant
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Speed and power are not the only factors between the series.
    There is also a difference in Fan-in (input current) and Fan-out (output current).

    The H and LV also have different powersupplies.

    [​IMG]

    Bertus
     
  3. disjaukifa

    Thread Starter New Member

    Nov 1, 2013
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    0
    Ok that chart is very useful. Pretty much everything I'm working with is right at +5 volts so from looking at that chart, I should be able to go from SN74S to a SN74F with no issues because the power range on the SN74F is great than the SN74S correct?

    Trying to find the input and output currents currently.
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,449
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    We can guide and assist you on this site with your repairs.

    Looking at the speed of the 74XX chips is most likely the least of your problems for your applications.

    There are times that you can interchange family types and there are times that you can't.

    74XX, 74LS series are still readily available and hence you should not have problems sourcing replacement parts.

    It is unusual for logic gates to go bad. There may be other reasons for your boards to malfunction.

    Your best bet is to post a circuit schematic if you have them available.

    Your second bet is to post a clear focused photo of the board and supply what you know about the function of the board.

    Then we'll take it from there.

    Edit: You cannot measure input and output gate currents easily. Just ignore that parameter for now.
     
  5. disjaukifa

    Thread Starter New Member

    Nov 1, 2013
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    0
    Thank you! I know for a fact right now I have a 74191 that is bad on my Missile Command PCB, I'm not getting any outputs and when the PCB is on that one chips gets ridiculously hot. I'm having deal with ICs that have rust or major oxidation, or something else that causes the legs to go bad. I'll see if I can find a schematic to post.

    -Grant
     
  6. MrChips

    Moderator

    Oct 2, 2009
    12,449
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    74XX logic chips should not get hot.
    Check your supply voltages. 5VDC is the most common supply voltage required for 74XX chips.
    Replacing a hot chip would be the next step.

    Do you have an oscilloscope?
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,649
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    Hallo,

    Also shorts between outputs of a chip may cause some heating.
    Check if there are no pins unwanted connected.

    Bertus
     
  8. disjaukifa

    Thread Starter New Member

    Nov 1, 2013
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    I've checked the power supply and all the test points across both the ARII, Audio Regulator PCB and the main PCB itself, thankfully Atari put several test points on their stuff. I've adjusted the voltage to +5.02 volts which I measured with my Fluke. My +12 volts line sees +11.75 and my -5 volts sees -5.2 volts.

    I do have an Hitachi Oscilloscope but I have never used it, mostly I have used it to test my various Vector games to see if I have a PCB or monitor issue.

    Asking about the 74XX vs the 74LS is where this all started. It seems the LS stuff is much more available and cheaper. So if I can replace a 74191 with a 74LS191 to save some money I would. Also I'm trying to a massive order of the all the parts that come on a Missile Command and various Atari PCBs, I have a stack of Missile Command and Asteroids PCBs I want to learn how to fix.

    I can already burn my own EPROMs so that is not an issue, I do have a Fluke 9010a and 9020a but I don't have a 6502 pod, which I need, I also have a HP 5004a that I haven't used yet, and a logic probe. I've been gathering equipment so once I moved into my house, which I just did two month ago, I could start working on all of this stuff.

    -Grant
     
  9. MrChips

    Moderator

    Oct 2, 2009
    12,449
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    Whoa! One thing at a time.

    Yes. For an old arcade game you can probably replace 74XX chips with 74LSXX chips and still be operational.

    Now would not be a bad time to dust off the oscilloscope and learn to be comfortable using it. Next to a DVM a scope should be your best friend.
     
  10. disjaukifa

    Thread Starter New Member

    Nov 1, 2013
    6
    0
    Yeah I have a Fluke 87 or 85, I can't remember, I purchased it used, but I use it with my Fluke High voltage probe to adjust the high voltage on my Vector monitor, both B&W and Color vector. I love my fluke.

    I don't really love my Hitachi Oscilloscope, its ok, but not great, thinking about getting another one, but I would love to get by with this one for the time time being.

    -Grant
     
  11. MrChips

    Moderator

    Oct 2, 2009
    12,449
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    Why do you want to use 74F00?
    Use a 74LS00 instead.
     
  12. disjaukifa

    Thread Starter New Member

    Nov 1, 2013
    6
    0
    Yeah I deleted that post because of the typo, I got confused at what I was looking at, and just deleted. Yes I want to use 74LS00 and from the datasheets I'm looking at, that would be fine for what I'm doing. My bad for the confusion.
     
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