Mystery Fuse Resistor...I'm stumped

Discussion in 'The Projects Forum' started by DickCappels, Aug 4, 2014.

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  1. DickCappels

    Thread Starter Moderator

    Aug 21, 2008
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    I hopeful that somebody knows more about color coding of fuse resistors than I. The burned part appears to be a fuse resistor -it is open circuit. All I know about the circuit is that it is a small switching power supply. It doesn't seem to have enough color bands on it.

    Input: 100 to 240 VAC, 0.15A
    Output: 5V, 0.7A

    My question is: What are/would the current ratings be, and what resistance?

    Thank you in advance for any help.

    [​IMG]
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    12 ohms, 10% tolerance, 1 watt is my guess.
     
  3. to3metalcan

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    Jul 20, 2014
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    Unless there are traces of another stripe in the burned area, I'd be inclined to agree...brown, red, black = 12 ohm. Hmmm...despite the board marking, doesn't really look so much like a fusible resistor as just a plain old flameproof metal-oxide...:rolleyes:
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Looking at the pcb marking it says " F1" maybe its a fusible resistor...0.12 ohms 1w ?
     
  5. to3metalcan

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    Jul 20, 2014
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    Dodgydave, so you think the silver stripe is the multiplier? Would that make the fuse a +/- 20% component, then (no tolerance stripe)?
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    maybe multiplier is a silver stripe(X 0.01) that's burned out :confused:
     
    Last edited: Aug 5, 2014
  7. to3metalcan

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    Jul 20, 2014
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    Sigh. Yeah. I've had SMT fuses burn out before that left no clue at all behind. How hard would it be to print the rating on the board?? Makes me want to find the manufacturer and administer some soldering iron justice! :mad:
     
  8. wayneh

    Expert

    Sep 9, 2010
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    How about looking at the opposite side?
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I'm guessing a 4 band value of "120 silver" or 120 /100 = 1.2 ohms.

    12 ohms is unusually high for that purpose. 1.2 ohms is much more typical.

    Similar diameter to a 4007 diode, so it is only a 1/2W package size.

    It is likely to be a DC line, so put in a 1.2 ohm resistor and run up the unit, and measure the voltage across the resistor then calculate the dissipated wattage. It should be <25% of the resistor wattage, so if it runs hot use a smaller resistance.
     
  10. DickCappels

    Thread Starter Moderator

    Aug 21, 2008
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    Thank you all for putting your minds to this problem.

    More information just in:
    Its a Samsung phone charger. The part in question is between the AC line input and the rectifiers.

    So far, I have not been able to find a fuse resistor datasheet that describes a fuse resistor with so few bands. Maybe, as suggested above, the only solution is to try a value and see if it gets too hot or not, then adjust the resistance accordingly.

    That still leaves the fusing current to consider, but the 0.15A called out on the label should provide guidance for that.
     
  11. THE_RB

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    Feb 11, 2008
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    12 ohms is definitely too high then.

    It would be a 1.2 ohms 1/2W fusible resistor.
     
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