I'm trying to repair damaged power supply. I've already replaced some burned/shorted diode and mosfets. Now I'm struggling with resistor connected between main mosfet's drain and ground. It should be probably 0.5 - 1 ohm one. My meter is reading 0.1 ohm, which is probably too low. I'm not able to read the value from the color stripes properly. They're probably violet, green, white (silver?), red and black. I'm guessing 0.75 ohm ww. Can somebody please help me to confirm this? I've tried to search similar questions, but the white stripe is confusing me.

What does a black band at the end of a resistor mean?

shorted resistor

I've temporarily tried to replace it by two 3.9 ohm 2 watts ones in parallel. Power supply seems to be starting ok with them. Haven't tried with higher load yet. With the original resistor, the main fuse gets burned immediately after powering on.

  • \$\begingroup\$ does the PCB have component labels? ... if yes, then what label is used for that component? \$\endgroup\$ – jsotola Jan 24 at 21:15
  • \$\begingroup\$ It's most likely a 4-band resistor (P,G,W/S,R) with and additional temperature coefficient (K), which is common for power resistors. I would guess the middle is probably meant to be silver, which would be 0.75R 2% 250ppm/K \$\endgroup\$ – Tom Carpenter Jan 24 at 21:20
  • \$\begingroup\$ There's R9 label for that components. But it's probably sequence number R1, R2, R3, ... Thanks for the replies, I would try some 0.75R power one. But I have to order such one first... \$\endgroup\$ – zeli52 Jan 25 at 8:10
  • \$\begingroup\$ Gaps between rightmost bands suggest red as tolerance 2% and extra black strip as either TCR=250ppm/K or a "noninductive" marking, at least according to here see also here. As for the third band, I don't believe it's 10^9 as stands here, likely it's either discoloured silver x0.01, or actually white x0.1 according this, note *.. so, either 0.75 ohm or 7.5 ohm. \$\endgroup\$ – quetzalcoatl Mar 9 at 16:01
  • \$\begingroup\$ That asterisks * in the table from the last link are a bit hard to see. Single asterisk * has a note of "Optional coding for applications where metallic pigments are undesirable". I can see how metallic paint may be undesirable in a PSU or some high-voltage device, but still, that's just a hunch. \$\endgroup\$ – quetzalcoatl Mar 9 at 16:03

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