Can someone tell me how to read this resistor value?
After reading When your 5 Band Resistor is not a 5 Band Resistor on the DigiKey forum I realized this is a 4-band resistor, and the 5th band is probably the temperature coefficient. However, it could be an indication that this is a non-inductive resistor.
From the link above: "If your 5th band is black you are best to try to identify the resistor manufacturer and look at their data sheet."
I don't know who manufactured it.
This PCB is the main board of a consumer washing machine. The stage in which the resistor is located seems to be a SMPS. Mains are connected across the yellow relay, bottom right, and black relay, bottom center. I'd say this is a 0.33 Ω shunt resistor, but I'd like to know if that last black band means just the tempco or if it is a non-inductive resistor. I can't measure it, since it is destroyed. Any thoughts?
I still can't measure anything, so what I am posting next is still hypothetical.
The SMPS controller is a STRW6052S. These were the best light incidences on the markings I got:
This trace in red comes from the bridge and caps, and goes straight to the aforementioned resistor:
Looking at the STRW6052S datasheet, pg 21, the main traces should be as wide as possible, and they come straight from the bridge + caps:
Also, on pg 23, Reference Design, we see that this is the only resistor rated for 1 W, or more than 1/8 W:
In the reference design it is R2, 0.27 Ω, a current detection resistor, very close to the 0.33 Ω on the physical board.
It also makes sense that the 1 kV ceramic disk cap and the resistors next are fried, since they are on the same path of the rectified mains voltage, which is about 537 V (380 VAC):
These resistors are 2x 470 Ω, connecting PIN1 to the snubber and the primary. They are not shown on the reference design, and I am not sure what they are doing there.
Now, here is the interesing part: the datasheet recommends that this current detection resistor should be a non-inductive part, pg 18:
So far I am inclined to think that this is actually a non-inductive resistor, and obviously should be replaced by another of the same kind.
Best Answer
It's probably a non-inductive 0.33Ω +/-5% shunt resistor used as part of a high-frequency switching power supply.
There is nothing lost in replacing an inductive resistor with a non-inductive in 99.99% of cases. The power rating can be estimated from comparing the physical size to that of other products at a distributor such as Digikey.
However, if it's gone then likely some other things have fried (at least some power semiconductor or semiconductors gone short) with the demise of the hapless resistor a mere consequence.