I would like to replace this resistor, but its color bands are faded. Does anyone know what resistor I should get for R31?


photo of resistor on PCB

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    \$\begingroup\$ If you cannot read the colour bars , neither can we \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 2 '19 at 0:39
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    \$\begingroup\$ Remove it and measure it with a multimeter. Hopefully those cracks are just superficial and it still gives a sensible resistance. \$\endgroup\$ – DKNguyen May 2 '19 at 0:45
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    \$\begingroup\$ Could it just be the same resistance at the same-sized one at the very right of the photo (200 ohms)? \$\endgroup\$ – Fleetie May 2 '19 at 12:43

If the resistor is still OK, though faded, you could measure its value. If it has failed, then you pretty much have to find a schematic with values, or another (identical board) where the resistor is still readable.

Assuming the resistor is OK:

Given how over heated that resistor looks, I'd be afraid of it falling apart if I tried to unsolder it completely.

What I'd do it use a pair of side cutters to clip the lead on one end, then raise it just a little so that the connection is open. Then I'd use a multimeter to measure the resistance.

Clip the lead right at the through hole. Be careful when you clip it not to wiggle the part around too much.

If you don't have a small pair of side cutters, you might use a pair of toe nail clippers (the clippers, not the nail scissors.)

In any case, clip the lead flush to the board.

Once you have the value, push the resistor back down so the leg makes contact with the clipped spot, then solder the leg back together. That lets your circuit keep working until you get a replacement.

Keep in mind the power rating. Under no circumstances should you use a resistor with a lower power rating. Use a higher power rating if you have room for it and can make it fit. The one you have seems to be a little on the small side (power rating wise,) so a higher rating would be a good thing.

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  • Measuring it is your best bet, if it does not work (because the resistor is fried, for example);

  • Given how old your circuit looks, there is a good chance the schematics are available somewhere online. (I've worked on old valve radios that even had them neatly stored inside the enclosure!);

  • Depending on the rest of the circuit, R31 could be part of a building block replicated somewhere else on the board (Look for R21, R41, R131,etc.);

  • As a last resort, deduction time!

    • its a gold band resistor (top band) which means its probably in the E12 series. This series goes like this : 1Ω, 1.2Ω, 1.5Ω, 1.8Ω, 2.2Ω, 2.7Ω, 3.3Ω, 3.9Ω, 4.7Ω, 5.6Ω, 6.8Ω, 8.2Ω times a power of 10.
    • The first color seems to be orange, which is color code for 3, so its either 3.3 or 3.9
    • Given the second (faded) color, is yellow, I'd assume its a faded orange, and go for a 3.3 value.
    • For the multiplier, measure the resistor's dimensions (length and diameter) to get the package and power rating, and use your knowledge of the surrounding circuitry to find the operating voltage and/or current. From there, use U = RI and P = RI² to find the final value.
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desolder it, remove it then measure the Resistance with an Ohmeter. that should do the job

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  • \$\begingroup\$ that resistor is visibly damaged, and OP's first sentence is "I'd like to replace it" – I don't think they want to replace it because it still has the original value. \$\endgroup\$ – Marcus Müller May 16 '19 at 10:44

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