Matched resistors

Discussion in 'General Electronics Chat' started by Gdrumm, Mar 21, 2014.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    When scavaging parts from an old board, there were two rows of resistors.

    In each row, two resistors at the end of the row, side by side, had been hand painted with a simple dot of silver paint at one end.

    Otherwise they had the same markings as the others in the row.

    Is it likely these are matched pairs?

    If so, why would matched pairs be required?

    Thanks
    Gary
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Could be polarity identification too u know
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    You're early. It's not April 1st yet.:)
     
  4. crutschow

    Expert

    Mar 14, 2008
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    The could be hand selected to provide a more precise parallel resistance than a single standard resistor can provide. If the string of resistors is a divider network then it could be to improve the accuracy of the divider voltage output.
     
  5. BReeves

    Member

    Nov 24, 2012
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    You do understand the only person that can really answer your question is the guy that painted the resistors.

    Hats off to the guys on this forum, they do try and sometimes succeed at answering impossible to answer questions.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Darn!
    And I thought I had him. :D
     
  7. BillB3857

    Senior Member

    Feb 28, 2009
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    We had a system manufactured by Getty Controls that was very confusing. The schematics provided had resistors marked without values but instead had the notation of AOT or AOR. That meant the designer didn't know what value to use but the value would be determined by Adjust on Test or when the control was completed and married to the machine, Adjust on Runnoff. Your silver dots may be an indication of such a procedure.
     
  8. Little Ghostman

    Member

    Jan 1, 2014
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    That just about describes every circuit I have ever built lol
     
  9. #12

    Expert

    Nov 30, 2010
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    The first time I met that, it was labeled, "select". That meant I had to calculate what it needed in Quality Control and add that resistor.

    as an aside,
    That particular design and solution seemed wrong to me because the designer had removed 3 or 4 parts that used to make a select function unnecessary. Something about cost reduction, but I have difficulty understanding why removing 3 or 4 ten cent parts could justify the extra 10 minutes at my bench. Probably the way the cost accounting was done that made the designer look good on paper while not really improving the cost of the machine.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Happens that way in other industries. I used to sell a product that cost a bit more than the traditional one, but reduced costs a lot in downstream finishing. The guy buying my product couldn't have cared less, because he wasn't responsible for the downstream or overall cost, just his little part of it. To be fair, they usually came around, but it was SO much more difficult a sell.
     
  11. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    In my business, parts come out of one budget, and labor from another, so the person who can seemingly trim budgets by saving on parts is the hero, and maybe the next VP. I've heard them say "well the labor is already there", meaning it's not factored into the equation until they fall behind and have to add another body.

    Of my business, we say it's a "pennies" business, meaning not much profit per unit, but hundreds of millions of units.

    Thanks for the insights.
     
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