I am currently in the process of trying to repair a power supply that has had one of its DC rails fail. A resistor in the PSU has exploded and I am trying to find what value it is.

Picture of resistor in question

Band 1: White
Band 2: Brown
Band 3: Silver (Possibly Grey?)
Band 4: Gold
Band 5: Green

The weird thing is that the middle band appears to be silver, which should be invalid as far as I can tell. If you assume the silver is grey (although this is unlikely, as there still needs to be a grey colour as well and the band is metallic), it produces a value of resistor which is incredibly uncommon to the point it does not exist (91.8 Ohms 0.5%).

Apologies for the noobie question, I'm just stumped after hours of trying to understand why this is and coming up short :).

  • 6
    \$\begingroup\$ Given the color of the resistor is already very close to grey it could be they opted for metallic as replacement for grey. If you neglect the green ring and treat it as silver, it turns into a 0.91 Ohm resistor which seems to be a value which is available and could be used as current sense resistor (Rs3 might indicate a "sense"). \$\endgroup\$ – Arsenal Nov 13 '18 at 9:13
  • 5
    \$\begingroup\$ Could the green ring be temperature coefficient? Making it 0.91 Ohms 5% 20ppm/K ? \$\endgroup\$ – Peter Karlsen Nov 13 '18 at 9:20
  • \$\begingroup\$ Can you trace what the resistor is connected to? This could give you some valuable clue what order of magnitude the resistance would be. \$\endgroup\$ – winny Nov 13 '18 at 10:03
  • 2
    \$\begingroup\$ Pretty sure @PeterKarlsen is right; when the fourth band is gold or silver on a five-band resistor, the fifth band is tempco. \$\endgroup\$ – Hearth Nov 13 '18 at 13:40

The comments above are right. Look at a 4-Band with a 5th temp coefficient band. Not all companies do this, however it is not uncommon either.

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