Need to repair a trace on my PCB. The burnt trace has a hairpin turn on it. Instead of following the same hairpin shape, can I just bridge across the undamaged points at the bottom? And also, the printed "TF b=0.4mm" on the PCB, does it have any significance to it? Next to it appears 0.6mm that has the same hairpin shape, but trace looks a bit wider. I have superimposed two pics together. One has light shone through the PCBpcb


2 Answers 2


Since they're labeled TF, it's safe to state they're thermal fuses.

Therefor, since inductance is likely irrelevant, you could replace them with through-hole fuses of the correct value. The current value depends on copper layer thickness, but for 1 oz. Cu, 0.4 mm would be about 1.5 A and 0.6 mm ~2.5 A... but it would be better to find out what the actual current ratings are.

N.B. Since that 0.4 mm trace is thoroughly fried, first fix the issue that burned it out. The fuse has a purpose, and it likely prevented further damage or even a fire, so don't just bypass it.


Keep the track shape, the design probably intended either forming an inductor from the trace or a thermal separation or fuse. Keep the wire's cross sectional area to be a similar size of the trace. If you do make a repair, make sure the root cause of the burned trace is identified, otherwise a wire repair may end up burning out also.

  • \$\begingroup\$ It could also be meant as a fuse. \$\endgroup\$
    – TimWescott
    Dec 20, 2018 at 0:14
  • \$\begingroup\$ Thank you for those who have answered. Besides the fried trace, there's also an exploded varistor (14D241K) on the other side of the PCB. The two legs above the burnt hairpin is where the varistor is soldered. I guess it's all part of the voltage surge protection. I plan to replace the varistor, just not sure how to proceed with the hairpin trace. Great input from you guys. \$\endgroup\$
    – Newbie ET
    Dec 20, 2018 at 1:13
  • \$\begingroup\$ @NewbieET meta.stackexchange.com/questions/126180/… \$\endgroup\$
    – Voltage Spike
    Dec 20, 2018 at 16:05

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