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This is a PCB from an induction cooktop. It runs on 400v. This trace blew because the wiring was crossed during installation of the stove. Compared to the exacto knife, the area is quite tiny.

How would you rebuild this trace; with what sort of copper material....wire, strip, custom? Any help is appreciated because it will save me having to buy another induction stove. Thank you.

After the overload

Compared to a new section

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  • 10
    This is probably better asked on Electronics.SE
    – Machavity
    Jul 7 at 16:53
  • 13
    Would try a electronics/computer repair shop. That might not be all that is wrong with that board. Other items might be damaged also and would need testing. 400v not something to fool around with.
    – crip659
    Jul 7 at 16:54
  • 5
    It is quite possible you only need to replace the PCB board, not the whole induction stove.
    – crip659
    Jul 8 at 12:11
  • 6
    If this was installed for you, ask the installer to replace it for screwing up. If you installed this yourself, follow @crip659's suggestion to contact the manufacturer or other 3rd party appliance repair/parts places to see about getting a replacement board instead of a full replacement stove.
    – FreeMan
    Jul 8 at 12:47
  • 7
    Another thing to consider: attempting to repair this might be seen as defeating a safety feature and could void your homeowner's insurance should your stove cause a fire. It's way less risky to just replace that one part.
    – bta
    Jul 9 at 0:28
69

That trace there is a fuse.

Notice how that trace is much narrower than the trace on the rest of the board. Notice how it blew neatly when overloaded, and wasn't just random destruction all over the cooktop, thus causing least possible damage to the cooktop.

It's the world's cheapest fuse, but it's still a fuse.

I suspect this makes sense from a design perspective because it was never meant to be the primary means of over-current protection. On large appliances like this, the primary over-current protection is usually the same breaker as protects the wires - the one in the service panel/consumer unit. I suspect that a mis-sizing or mis-application of those might be a factor here.

Replace it by repairing the PCB per factory advice, or replacing entirely with a factory approved part.

You could solder heavy wire across it, to make sure it never blows here again, but then, it will just blow out somewhere else that is more destructive or more dangerous. And then you will need a new cooktop, or possibly, a new house. Or family.

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  • 13
    Not sure why downvoted, but -in general- traces are used as fuses. Whether OP's trace is a fuse we don't know, and caution with over gauging is warranted. See electronics.stackexchange.com/questions/200350/…
    – P2000
    Jul 7 at 17:15
  • 12
    It's possible that there is other damage on the board, when electronics fails fuses tend to blow second,
    – Jasen
    Jul 7 at 22:37
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    And considering it is a FOUR HUNDRED VOLTS appliance, you can be certain it's going to be some big damage. You don't really want to mess with this a whole lot.
    – Nelson
    Jul 8 at 7:07
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    @Sam oh come on... I can't win! I just changed from that answer to "replace the assembly per factory reco" after someone else DV'd me for suggesting repair. Why don't you write an answer describing exactly how to determine the trace size, don't forget trace thickness... I for one would like to know how you measure that. Jul 9 at 2:49
  • 4
    +1 for "oh come on... I can't win! " would have upvoted you before but was too busy modifying mine.
    – JACK
    Jul 9 at 11:28
8

I would get 4 or 5 short strands from 18 gauge stranded wire and pull them out of the insulation and twist them together. Tin them with solder and place them across the two terminals, hold in place with a small screwdriver and solder them in place. I would not use heavier wire because as Harper pointed out, those missing links are acting as fuses.

I would not recommend you doing this yourself as it's very high voltage and there are unknowns about the fuse sizes required.

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  • 7
    This narrow trace is a fuse, replacing a fuse with a wire is generally considered to be a bad idea.
    – Jasen
    Jul 7 at 22:32
  • 1
    @Jasen That's why I said a few strands from 18 gauge wire. Do you know how small those are?.... That about the same ampacity as those traces which, by the way, are not calibrated exactly as fuses are.
    – JACK
    Jul 7 at 22:52
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    +1, for editing and adding the caveat that they could be fuses and should not be over-gauged.
    – P2000
    Jul 8 at 0:20
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    Every single answer got pinched with a DV, including the question (so the DVer is not the asker unless someone retaliated). Someone thinks they know better than us all, but won't share. Tsk tsk... Jul 8 at 0:39
  • 1
    @Jasen OK, a few strands from 18 gauge stranded wire.
    – JACK
    Jul 8 at 1:27
3

Rather than debate the best way to bridge this defect, I'd like to highlight the question whether it should be bridged:

Some electronic components and devices fail "safely" and others fail "unsafely". Those that fail unsafely require a back-up mechanism to effectively achieve a safe fail. That trace may be precisely such a provision.

Consider, for instance, capacitors that can blow and short, or blow and open. Similarly, transistors & switches can fail by opening or by shorting.

Sometimes the open-fail is preferred, and sometimes the close-fail is preferred. Which one is required depends entirely on what goes on elsewhere in the circuit or system: what is the overall effect of as an open and what is the effect of a close?

Consider the similar question, whether a valve should break open or break closed? The answer cannot be provided in isolation; it could depend on whether it is for a gas line or a sprinkler system.

Back to the stove: that trace fuse may have been deliberately designed for that spot in the circuit. It blew because of a failed component or sub-system (a transistor, a relay, capacitor), and that component possibly failed unsafely. The fuse may have been specified there to prevent consequential damages: a further current surge (fire), an exposure to high voltage (electrocution), or an uncontrollable over heating (toxic fumes).

If it was human mishandling that caused a fuse to blow, and the cause is now removed, then replacing a replaceable fuse would be fine of course as a first attempt to repair.

But if the mishandling caused a different component to fail, as a result of which the trace blew, then jimmy-rigging it will only expose the user to the mitigated secondary hazards (fire / electrocution / toxicity).

The (e-)waste in such a catastrophic event pales against the e-waste from preventative repair or maintenance.

Given that this trace that blew was not marked as a fuse, take it as a hint that fixing the fuse is not to be attempted. Rather, the entire board and stove should be inspected by a qualified technician who is insured to take on the liability of a mis-diagnosis.

2

Of course I have to be the devil's advocate. Just scrape the pads and solder bridge it. But first check any big resistors that are mounted 1/4" off the board with an ohm meter. And also check your IGBT transistor. They fail when you whoopsie installation.

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  • 2
    That's not such a bad idea. The conductivity of solder is much worse than people realize, so a solder bridge would make a passable fuse, especially since it doesn't need to vaporize, just melt. Jul 8 at 0:41
  • Caveat being the load on those blown 'fuses', what is on the other side of that PCB? Jul 8 at 1:46
  • 1
    @Harper-ReinstateMonica That might be an issue in itself. This is a cooktop, so we're likely talking about >10 A through that solder bridge, in an already hot environment. The solder might melt in normal operation (perhaps it's best to use one of the "fireproof" lead-free solders).
    – TooTea
    Jul 8 at 9:13
  • -1. This board has been damaged and OP is still alive, giving us a hint that it's safety features worked. Following your advice, without intimate knowledge of how the board works, is akin to bypassing safety features. Devil's advocate, indeed.
    – LShaver
    Jul 8 at 23:30
0

What load is it carrying ? Depending on that I would likely find wire to solder to the two largest common terminals on either side of the break.enter image description here

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  • 3
    -1. This board has been damaged and OP is still alive, giving us a hint that it's safety features worked. Following your advice, without intimate knowledge of how the board works, is akin to bypassing safety features. Possibly OK for a hobby project, but unethical for a household appliance that others besides OP will presumably be using.
    – LShaver
    Jul 8 at 23:30
  • Hence my comment starting with "what load it is carrying?" The component side of the board is never seen. 24V<= with minimal current draw bridging would be fine. 110V not so much. I presumed if the guy had taken it apart and was going try and repair it he would know as much. Jul 9 at 19:38
  • The voltage between the pads in question is definitely not low - the board wouldn't need those creepage slots for low voltage. It's reasonable to assume those pads are at line voltage (i.e. 120V minimum, at least 240V more likely for a cooktop; and the OP says the unit actually runs on 400V).
    – nobody
    Jul 10 at 13:35
0

I would guess that board is 1oz copper clad, that's pretty typical. That makes it 0.0348 mm thick. Guessing from the Exacto photo, the trace is maybe 1mm wide (measure it to be sure). so width(1mm) * .0348 = 0.0348 mm2 cross section. looking that up on a wire chart : AWG Cross Section (mm2) 32 0.0320

so a single strand of tinned 32AWG is what I would use.

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  • 3
    -1. This board has been damaged and OP is still alive, giving us a hint that it's safety features worked. Following your advice, without intimate knowledge of how the board works, is akin to bypassing safety features. Possibly OK for a hobby project, but unethical for a household appliance that others besides OP will presumably be using.
    – LShaver
    Jul 8 at 23:53
  • 3
    @LShaver Indeed, though the OP would probably be alive anyway without the safety feature. The real risk is now, after bypassing it, there will be one less safety feature.
    – user253751
    Jul 9 at 16:36
  • @LShaver. I (attempted to) calculate the wire size that will still act like the original PCB trace. please explain how that is "bypassing a safety feature"? Cutting and pasting your previous comment to a different answer is pretty lazy.
    – Mark
    Jul 17 at 3:21
0

Replace with the internal metal strip of an actual properly rated fuse.

As mentioned, those were acting as a fuse, so you should replace with a properly rated fuse and not remove the safety feature by solder or wire bridging it. It's easy enough to buy a few glass fuses at the hardware store and either retrofit the fuse with a fuse holder or dismantle the fuse to get the "fuse metal" and solder that across the terminals. At least if this happens again, the fuse metal will melt as the PCB trace did.

edit: The question is how do you determine the original fuse amperage accurately? As @LShaver mentions, it may not be the total appliance load. Take the wattage of the appliance, divide by 400v to get the amps, add 1.5x to 2x headroom to get the fuse amp rating.

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  • To you point, this might not be carrying the full appliance load and I don't see enough information to ascertain that. Jul 9 at 21:17
-3

I would simply use two single 22 gauge copper pots (plain old telephone system) wires soldered across the burnt trace area. Simple is the best way to go about these repairs most every time my friend. That said, I would carefully test to see if that restores complete functionality. If not continue trouble shooting. If so, then carefully test the repair through the range of the stove's functions to determine if there is any need to strengthen the bridged trace.

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