Big Problem

Discussion in 'General Electronics Chat' started by supermankid, May 22, 2014.

  1. supermankid

    Thread Starter Member

    May 26, 2013
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    Hi, I used a wrong part (comparator instead of opamp)...Now the board is ready...is there a way I can find replacement for this comparator....with opamp with similar pinnning .....I want to use as a buffer...low bandwidth...so..any opamp could fit in....help me!!!:eek:
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    So do we just guess at a schematic or part number or footprint of this wrong part?
     
  3. R!f@@

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    Apr 2, 2009
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  4. t06afre

    AAC Fanatic!

    May 11, 2009
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    Eh..please share what kind of comparator you are using. And also share your schematic
     
  5. supermankid

    Thread Starter Member

    May 26, 2013
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    I was having slight inkling today...felt like I was missing something....and it had to be this....here is the schematic....which would actually make no sense...but the part number is LM319 from Texas picture.JPG
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    You're right. Why did you post it?
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Other than open collector outputs, are there any other reasons to change away from the 319? If OC outputs are the only problem, can you add pullup resistors to the board after fab?

    ak
     
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    time to learn to cut traces/install jumper wires.. :)
     
  9. supermankid

    Thread Starter Member

    May 26, 2013
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    The main reason is...this is a comparator ...I need opamp. I am desperately waiting for some help.
     
  10. mcgyvr

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    Oct 15, 2009
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    Go to digikey.. search for an op amp.. filter by package.. read the datasheet. see if any are close enough..
     
  11. crutschow

    Expert

    Mar 14, 2008
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    So you built the PC board without doing a breadboard first? Bad. :eek:
     
  12. ErnieHorning

    Member

    Apr 17, 2014
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    Whichever part you use, you should tie your unused amp inputs to something. Typically ground, since its right next to those pins. If ESD doesn’t nail them, the part will use excessive current as those high impedance pins pick up any noise in the air.

    It’s a good design practice to get in the habit of tying all unused inputs to something anyway.
     
  13. MrChips

    Moderator

    Oct 2, 2009
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    How many boards do you need to assemble?

    Here are some options:

    1) patch the board
    2) make an adapter PCB to fit the current footprint and pin-out
    3) redo the board
     
  14. supermankid

    Thread Starter Member

    May 26, 2013
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    I went through 320 opamps of same package from digikey...no luck....
    picture.jpg


    It is only about 20 PCB.....

    I am thinking about some kind of adapter....I will post the picture when I am done...!!...this really suckss.....:(
     
  15. t06afre

    AAC Fanatic!

    May 11, 2009
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    How many layers is your board. And what kind component type is the component type in question. Is it SMD or through-hole. Last question can you blame someone else for this mishap:p
    Either way I think the board can be salvaged with some strapping, since it is only 20 boards we are talking about.
    Edit forgot about this trick. Mount a through-hole opamp upside down and glue it to the board with super glue. Fold the thin part of the component like a gull wing. Then use the strapping technique to correct your your mess
     
    Last edited: May 22, 2014
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  16. THE_RB

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    Feb 11, 2008
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    Go for an adapter. Just use an 8pin socket with 8 wires on its pins. You could of had it done by now. ;)
     
  17. BobTPH

    Active Member

    Jun 5, 2013
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    But how is that going to look to the customer?

    IMHO, bite the bullet and redo the PCBs.

    Bob
     
  18. Lestraveled

    Well-Known Member

    May 19, 2014
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    The pin out of a LM319 is unique. You will not find an op-amp that will drop in. I suggest two options:
    1. (Bad option)- try to make the comparator act like an op-amp. The LM319 is really fast. Feed back resistor, pullup resistor, and output cap to ground will be needed. Look at circuits that make comparators into op-amps.
    2. (Best) Select an op-amp that works for your application. Get a wire-wrap socket and artfully bend the pins to match your PCB pattern.
    Calm down. Everyone who designs PCBs gets to do this every so often.
     
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  19. THE_RB

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    Feb 11, 2008
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    Ahah! I missed his later post saying it was "20 boards".

    Still a little adapter (x20) is no big deal, compared to a complete board redesign.

    Many people would be surprised how many commercial appliances have tracks cut, wires soldered from point to point, and even little addition PCBs added in with hot melt glue and fly wires. ;)
     
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