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Hey everyone! Thanks for the replies. Before I get to them, I opened up the other side of the hair straightener and found some more components. Nothing visually seems to be wrong with the components on this side.
It is difficult to fault find at a distance, but at a guess the switch has burnt out. Does it smell. Is it now hard to move.
I don't think the diode (1N4007) plays any part in the heating function. I think it, and the resistor are there just to illuminate the LED. It is unlikely that any of those components would have failed by an over voltage of 20V.
What electronic skills do you have. Do you have a multimeter and soldering iron etc. If not it will be impossible and dangerous to progress any further. Please let me know.
I don't mean to be unkind, but as the hair straightener is 7 years old. I would strongly advise you to junk it and buy a new one.
Hey Spec! Thanks for the welcome and reply. It is a shame, isn’t it?
Following your lead on the switch, I noticed that it doesn’t seem to have any odour and it’s also not hard to move. Hmmm… Regardless, thanks for the information about the diode and resistor. I’ll note that I can probably rule them out as the cause.
As far as my electronics skills, they are very basic. I have a multimeter, a soldering station, and some other tools. I’ve practiced soldering a bit and have built a couple of small hobby projects from kits. I really have no technical understanding about electronics. I can basically follow recipes like a baker would, and that’s it.
*grins* It’s not unkind at all! I’m just a bit too stubborn to let go without trying something.
Hi,
I would say the heating elements have failed short circuit, running at 120v versus 100v would be a ~40% overdrive.
A short should have blown the plug safety fuse, if not, the switch has burnt 'open'.
The LED may have also failed.
Hey Eric! Thanks for the feedback on the different components. I’m actually surprised that I don’t see some type of safety fuse anywhere.
Anyway, following your lead, I’ve used my multimeter to test along the heating elements, switch, and LED for continuity to see if I can determine what has stopped working. The switch shows continuity on both sides, the LED shows continuity, and the elements show continuity from one solder pad to the next.
For what its worth,
My wife's straightener from time to time keeps making beeping sounds. (Beeps once when you plug it in and then it should be quiet).
I found that the rotary connection (where the power lead enters the straightener) opened up a bit, causing bad connection. I just used pair of long-nose pliers and closed the gap down again. The worked fine for about a year, and then did the same thing again. Having fixed it once before I did the same procedure again. We are still within our second year 
I noticed that the problem you’re describing was all over the internet while I was researching hair straightener repairs! I’ll keep my eye out for that problem on mine too, thanks!
That's like "no big deal".
You basically have a switch, a lamp and a heating element.
The lamps consists of the resistor, LED and diode. All standard.
On your PCB picture, it looks like you have a broken trace. Follow the blue wire.
The switch or the heating element could have failed or the trace itself was the only failure.
I don't like the blob between the two switch contacts.
The PADS labeled PTC was probably for a a ZNR which is a surge protection device.
Amazing! After I cleaned up the carbon on the board with some isopropyl alcohol, I can also clearly see the broken trace on both sides of the board.
I checked along the various components for continuity, and unless I’m mistaken, after mapping out what has continuity, it seems like it’s just the trace that’s the point of failure.
Here’s an image showing what I found. Anything connected with a red line has continuity among each other. A green circle is a component point, a black slash is where continuity is lost. An arrow shows continuity but only in that direction.
After doing a bit of research on how to repair burnt circuit traces, it seems like many people suggest using a small piece of tinned wire along the broken trace.
Would I use the tinned wire from the two components on either side of the trace? It seems like the trace encompasses two components at once on the far left. Hmmm... I'm a bit unsure of the safest way to do this.