SMD C0mponent attached to the back

Discussion in 'General Electronics Chat' started by Gdrumm, Oct 10, 2012.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I bought an Ebay LCD Projector for parts/repair, thinking it might be an easy fix. Turns out part of the board is fried.

    A bank of 6 Standard and Extended Rage Surface Mount Tantalum Capacitors has 2 that are blown and 1 is burnt.

    On the back side of that bank, one set of the 47 20V Captants has a small blue chip attached to it. The fine print on the small blue chip reads 1 R0(zero).

    I searched, but couldn't find it. I'm guessing it is an SMD Resistor.

    Does that make sense?

    If so, what exactly am I looking for?
    What is the name of the small blue chip, and what do the numbers mean?
    What does it do? Does it act as a filter?

    Elsewhere on the same board, another small chip like it is piggybacked onto another set of Captants, and the fine print on that one reads 4 R7.

    Any help is greatly is appreciated.

    The traces are clean enough, I think I can repair it, if I can ID the small blue chip.

    Thanks,
    Gary
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    Those sound like surface mount resistors. 1R0 is 1 ohm as "R" means a decimal point. Similarly 4R7 is 4.7 ohms.

    Measure the size and you can find a match from many places.
     
  3. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Thanks Ernie
     
    Last edited: Oct 10, 2012
  4. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    On the back side of the board, where I thought perhaps a small blue resistor was mounted, after I cleaned the area thoroughly, it appears that there was a larger component there instead. Based on the size of the blow out, and the traces I can see leading to the area, I now believe it was another 47 20v Captant. (There are others nearby). The projector is old enough I can't find a schematic to be certain.

    Anyway, my question... part of the green enamel surface was blown away when this SMD blew. The missing enamel reveals a cross hatch of tiny copper wire underneath.
    What can I use as a filler to cover up these bare wires?

    Hope my question makes sense. Would a small bit of electrical tape work?
    Should I mix up some two part epoxy and coat the area?

    Thanks,
    Gary
     
  5. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I did fiind the Service Manual at fixdevice.com.
    I'll post back
     
  6. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Okay, I've got this far.
    There are three of the 1 R0 resistors in tandum, one is intact, and the other two are gone (with the board damage as described above.

    So I still need guidance on re-coating the damaged spots, but I have another problem.

    The schematic show these items as 1 uh 20%, whatever that is.
    When I looked on Digikey, there were a lot of choices, most called inductors?

    I measured the good one that remains, and , it is 3mm long, 2 mm wide, and 2mm tall.

    Any tips on how I can narrow the search?

    The picture of the Degikey results are small round parts.

    The parts I need, are rectangular.

    Sidebar, can I use a non surface resistor across the traces, instead of Surface Mount.

    Thanks,
    Gary
     
  7. BSomer

    Member

    Dec 28, 2011
    433
    106
    1 uH 20% = 1 micro Henry 20% tolerance. This is an inductor.

    Can you post some pictures and/or schematics of what you are looking at? That will help us help you.
     
  8. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Thanks all, and thanks Bsomer.
    I found the exact item on ebay, 20 pieces for 4 bucks, free shipping.
    It even bears the same markings.

    I'll post back when I have all the parts assembled.

    Gary
     
  9. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Back to square one.
    They weren't inductors (my bad).
    I've found that they are BS 1852 Coded 1 ohm Resistors.
    I've ordered a few (from China).

    However, I found some 4.7 ohm resistors of the same type / size on an old board I had laying around. Could I use these instead, or would it be a bad idea?

    Is it possible that a 4.7 ohm would do the same job, only better, or would it be an incorrect fix.

    Thanks,
    Gary
     
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