Fault from powering with incorrect voltage

[KatGND]

Good day everyone!

I have a hair straightener that I’d like to repair. Recently I was traveling and I was powering the device with a voltage converter that delivered too much voltage. The device is rated for 100V, and the converter delivered 120V.

The straightener worked for a while, and eventually I heard a pop, and the device failed. If I plug it in and try to turn it on, the LED doesn’t light up and the heating elements don’t warm.

Looking at the underside of the PCB, I can see that there’s quite a bit of carbon residue around some of the solder pads. The scorching seems to come from the Vin and GND connections. There’s no scorching on the top of the PCB where the components are located.

None of the wires on the device look like the plastic melted. Also, some of the wires are a bit more exposed than I’d expect. I’m not seeing that any of the exposed wires are touching each other. Though, some of the exposed wire do touch the PCB around the edges.

All of the components look just fine… unless there are components inside the second half of the device. I didn’t disassemble that half.

I’m fairly new to hobby electronics and my electrical theory is very limited, but I want to learn! I’d be so grateful for any guidance on how to diagnose the exact problem and how to subsequently repair it.

Summary
Device: Hair straightener
Brand: GAMA Italy
Age: 7+ years
Cause of fault: powered with 120V when rated for 100V
Symptom: Popping sound, device does not warm and LED doesn’t light. Bottom of PCB scorched

Images
Overview of device

Closeup of top of PCB that receives voltage input

Reverse of PCB

Some images showing the components on the top of the PCB

 

[duke37]

There are very few components abd they are all labelled.
I would think the switch is faulty, check that the switch is making a contact with a meter.

The solder on the switch looks as if it has been overheated which could happen it the switch does not turn on fully.

 

[(*steve*)]

I would check for continuity through the elements. If either is blown replacement is likely to be a new hair straightener (unless you can find someone with the same model with the other element blown) .

 

[KatGND]

Reply to electronics Point

Hey everyone. Thanks for the replies duke and steve.

There are very few components abd they are all labelled.
I would think the switch is faulty, check that the switch is making a contact with a meter.

The solder on the switch looks as if it has been overheated which could happen it the switch does not turn on fully.

Great suggestion. When I tested the switch in it’s open position, I found it has continuity through all 3 pads on each side, but not between both sides. I believe this rules out the switch as the source of the fault.

I would check for continuity through the elements. If either is blown replacement is likely to be a new hair straightener (unless you can find someone with the same model with the other element blown) .

Ah! Great idea. Just looking at the solder pads where the heating elements connect, there’s no exposed wire to test each element separately (if that’s even how it works). Also, I think these elements are wired in series, because the solder pad coming from Vin has one element’s blue wire and another’s black wire. The other solder pad going towards GND is the same, having one element’s blue and one element’s black wire.

Regardless, I tested for continuity at the two solder pads leading from Vin and GND where the wires for the heating elements connect. There is continuity.

I cleaned up the board with some isopropyl alcohol to test different points for continuity and noticed that there’s a spot on each side of the board where continuity has been broken. I wonder if this was some type of fuse made out of circuit trace, or something…

Here’s an image showing the cleaned-up board:

Here's a graphic trying to demonstrate what points have continuity. 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.

Here's a side-by-side with the board’s top components for reference.

Also, I opened up the other half of the straightener to see what was in it and if there was any damage. It seems fine.

I wonder if it’s possible, or even advisable to scrape off some of the green material covering the circuit trace there and bridge the gap with some solder. Or, perhaps solder a short wire from one solder pad to another where that connection is broken.

 

[duke37]

This is more complcated than I thought. The anion generator could be a problem if it has been overvoltaged.
You will need to draw out the circuit diagram and remove suspect components to isolate the fault.

Do not scape off the green covering, it helps the insulation. Only bridge contacts if you are sure they should be connected.