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Part required or is another suitable

Discussion in 'General Electronics Discussion' started by ivylodge41, Sep 15, 2016.

  1. ivylodge41

    ivylodge41

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    Dec 30, 2013
    Morning,
    I am looking for a part 74HC152D it has 8 legs each side & surface mounted.
    I can only seen to see 153 when searching.
    On this pcb there is plenty of room in respect of height so another variation is ok as opposed to surface mount.

    Please advise if you can assist.

    Thanks.
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
  3. ivylodge41

    ivylodge41

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    Dec 30, 2013
    Thank.
    That item has 7 legs each side ?
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Yes, it has. I haven't counted the number of pins in your photo (and obviously skipped that part in the text where you say it has 8 pins per side:rolleyes:), but as the chip you show has 16 pins, it is probably not a 74HC152.

    Could it be that the part in question is not 74HC152D but 74HC1520?
     
  5. ivylodge41

    ivylodge41

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    Dec 30, 2013
    I will check and confirm very soon.
     
  6. ivylodge41

    ivylodge41

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    Dec 30, 2013

    Attached Files:

    • 99.jpg
      99.jpg
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  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Should be fine.

    Do you know how to remove and replace those chips?
     
  8. ivylodge41

    ivylodge41

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    Dec 30, 2013
    I think so but its not a job for me as i dont have a work station etc ?
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    The chip looks o.k.

    To remove the old chip without special tools, use a fine wire cutter and cut the pins of the existing chip near the body. Thus you can remove the plastic housing and then de-solder the pins one by one which should be rather easy.
    Clean the pads, making sure the surface is as even as possible (use solder wick, if necessary, to remove excess solder. Place the new chip on the PCB (note correct orientation!). Fix the new chip by soldering diagonally opposite pins (e.g. 1 and 9), then solder the remaining pins. Use an iron with a fine tip, wait a few seconds between soldering pins to allow the chip and the PCb to cool down a bit.
     
  10. ivylodge41

    ivylodge41

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    Dec 30, 2013
    Thanks for that.
    I have ordered 3 chips and some fine solder.
    I have a gas cat soldering iron.
    Some info for you.
    This pcb is connected to a key programmer.
    At a certain stage in the key programmers job it then needs to look at this pcb,this was fine up untill say 2 days ago.What i see on the screen is awaiting module,this is the same message as it this pcb was not connected.
    I have another pcb of which when connected it is seen & the job continues.If i connected this pcb up again i see awaiting module so i know the problem is this pcb.

    On the pcb in question leg 1 is bridged to c7 capactor and leg 2345 are bridged together.
    This is all that has been done & was working fine.then nothing so is there a way to check if this chip is working correctly with a meter ?
    Or must i take it off first before checking.

    When the new chips arrive i will show image of pcb board first to ask if you see problem as strange it was working now no connection etc.

    Thanks
     
  11. Harald Kapp

    Harald Kapp Moderator Moderator

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    The 74HC series are CMOS components and as such especially vulnerable to ESD (electrostatic discharge). Since you seem to be connecting and disconnecting this board repeatedly, chances are that some electrostatic discharge may have rendered the chip dysfunctional. Observe good ESD measures (ask your favorite search engine) to minimize such risk.
    A multimetre alone will not sufficient to check the functionality of the chip - at least not without building a not so simple test rig around it.
     
  12. ivylodge41

    ivylodge41

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    Dec 30, 2013
    ok
    I understand,so now i await the new chips.
     
  13. ivylodge41

    ivylodge41

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    Dec 30, 2013
    Hi,
    My 74HC153D chips have arrived.
    Going by the advice given above i have managed to removed the chip from the pcb quite easily but i think there now is an issue of which might explain why the item stopped working.

    My plan was to replace the 74HC153D chip to the board,then for the item to work i had to bridge C7 (1) to first leg on chip (2).
    Then i needed to bridge legs (3,4,5,6) together,then job complete.

    But the problem i see is there are no solder tracks etc on the items marked "x" in the photo.
    The only solder tracks i see are marked with a tick.
    Just because there are no solder tracks there does that mean it can still be ok as i done see anything connected to the majority of them.
    As you can see this isnt my field.
     

    Attached Files:

  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Perhaps a photo of the board will tell us much more than your drawing.
     
  15. bigone5500

    bigone5500

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    Apr 9, 2014
    Could be that the leads are not meant to connect to anything..and/or are bridged together for internal purposes.

    Just a though.
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It looks to me like it is hard wired to load a particular value, one where most of the bits are the same.
     
  17. ivylodge41

    ivylodge41

    19
    0
    Dec 30, 2013
    Morning,
    Bear with me on this please.
    Supplied are 4 images.
    Pcb & also Pcb showing where i make the joins.
    There is also the lead i use to connect an item using RS232 to this pcb RJ11,as you see only 3 wires are in use.
    Pin out for chip 74C153D
    Two red arrows are joined together,then the 4 coloured arrows are joined together.
    Without these joins my two items do not talk to each other.
    Making these joins then they work perfect.

    Thanks
     

    Attached Files:

  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You have ripped a number of pads from the board when you removed the old chip.

    Whilst it might be arguable that some of those pads were not there in the first place, it is undeniable that the gnd pin (8) would have had a pad. Also the trace running under the chip would have lead to a pad.

    To fix this properly we will have to figure out where all of these went.

    The chip probably sets some sort of code which keys two devices together. Whether this is some type of selective call or frequency offset, or something else, there is insufficient information to determine (and its probably not important.
     
  19. ivylodge41

    ivylodge41

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    Dec 30, 2013
    I do have another but chip is on the board.
    Can I advise anything for you from that one ?
     
  20. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    On the other unit, can you confirm there is continuity between pin 6 and the via at the end of the trace coming from under the end of the chip between pins 8 and 9?
     
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