Need help repairing a mirror with a built-in light.

[halleffector]

Context: I have a mirror with a light built in. It doesn't work.

I can see that it gets power, from AC to DC, 12 volts.

I suspect one of two things might be broken.

1: The microcontroller that dims the light with what I guess is PWM. I'm ignoring this for now.
2: The touch sensitive switch.

How can I test this touch sensitive switch to see if that is the broken part?

The switch has three wires. +12 volts and ground, I assume, and a third wire. The switch itself has a small built-in LED that lights up, I assume it uses the power for this, and the third wire is the signal wire which is, what, pulled to ground, when it is touched? How do these things typically work?

All three wires going into the switch are coming from the microcontroller.

Can I just short the "signal" wire to ground, to test the switch? I tried shorting both signal to LED+ and signal to LED+ (one at a time) with a reasonable resistor. That didn't do anything.

Any ideas?

Here is a diagram.

I unfortunately don't know what "L1" and "L2" is. I know it can dim the lights and also change the color of the lights. Perhaps one of the L signals is for PWM and the other is for color?

 

[rjenkinsgb]

I'd expect LED 1 and LED 2 (L1 & L2?) to be different colours, and the PWM proportion of power to each gives the colour control?

I thing that briefly linking L1 or L2 to the GND terminal should put each LED on at full brightness, so you can tell if the LED lamps are still OK.

For them to work on 12V there must be either chains of LEDs with resistors or some form or current regulation in the lamp assemblies themselves, so it is possible for those to fail over time.


The touch switch likely works on either AC "hum" pickup, or by body capacitance grounding a small AC signal the electronics puts on the touch sense point.

 

[halleffector]

I'd expect LED 1 and LED 2 (L1 & L2?) to be different colours, and the PWM proportion of power to each gives the colour control?

I thing that briefly linking L1 or L2 to the GND terminal should put each LED on at full brightness, so you can tell if the LED lamps are still OK.

For them to work on 12V there must be either chains of LEDs with resistors or some form or current regulation in the lamp assemblies themselves, so it is possible for those to fail over time.


The touch switch likely works on either AC "hum" pickup, or by body capacitance grounding a small AC signal the electronics puts on the touch sense point.

Thanks!

Indeed, just before I saw this I tested shorting L1 and then L2 to GND, and it then lights up at full power on either completely "cold" or completely "warm" light.

I also tried touching both L1 and L2 at the same time to GND, that simply turns off the light completely. Not sure if it likes that to be honest (it still works fine on just L1 or L2).

I'm still curious how I can "emulate" the touch signal though, any ideas? I tried tapping both LED+ and LED- to "Touch" with a resistor, but I have no idea what resistance would be ideal, or if this is even the correct approach. Can I just short it directly?

 

[halleffector]

I dug out the switch, the LED+ and LED- literally go to an actual small LED, which is a completely separate component from the switch. The switch is just a single wire attached to what appears to be a flat metal plate embedded in a piece of plastic.

 

[rjenkinsgb]

That's typical, it will work from capacitive coupling by one of the methods I mentioned earlier.

The component below the "7133" appears to be a HT7133 voltage regulator to supply the control IC at 3.3V

Can you check the voltages on all the pins on that to GND? And between the two unused holes just left of it; that's also its output, I think?

Note that with a lot of ICs, applying any voltage higher than it's own supply to any pin can damage them.

 

[halleffector]

That's typical, it will work from capacitive coupling by one of the methods I mentioned earlier.

The component below the "7133" appears to be a HT7133 voltage regulator to supply the control IC at 3.3V

Can you check the voltages on all the pins on that to GND? And between the two unused holes just left of it; that's also its output, I think?

Note that with a lot of ICs, applying any voltage higher than it's own supply to any pin can damage them.

I might have broken it when I touched the LED- on the left side of the board with my oscilloscope probe without having the probe ground connected. The LED for the switch went off and didn't come back on.

 

[halleffector]

That's typical, it will work from capacitive coupling by one of the methods I mentioned earlier.

The component below the "7133" appears to be a HT7133 voltage regulator to supply the control IC at 3.3V

Can you check the voltages on all the pins on that to GND? And between the two unused holes just left of it; that's also its output, I think?

Note that with a lot of ICs, applying any voltage higher than it's own supply to any pin can damage them.

The touch switch LED (not the light itself in the mirror) just turned on again by itself! It blinked once, then after some time, it lighted up again. Maybe I didn't break it after all. Now it stays on like before.

I measured the voltage regulator like you asked, provided a picture.

 

[Les Jones]

It looks like the voltage regulator IC has failed. with NO power to the board measure the resistance between the negative supply connection (Ground) and the left hand. (In your picture). This is the output pin according to the data sheet. If you get a low reading (Less than 100 ohms.) then something on the output is probably causing the fault. If you don't get a low reading the regulator IC is faulty and needs replacing.

Les.

 

[halleffector]

It looks like the voltage regulator IC has failed. with NO power to the board measure the resistance between the negative supply connection (Ground) and the left hand. (In your picture). This is the output pin according to the data sheet. If you get a low reading (Less than 100 ohms.) then something on the output is probably causing the fault. If you don't get a low reading the regulator IC is faulty and needs replacing.

Les.

Thanks!

I'm not sure what you want me to measure. I did measure the VDD pin on the ADPT005. Apparently this thing uses a five channel touch IC. Not sure why it needs five channels. But anyway, between VDD and GND (using the GND on the right side, but this shouldn't matter) I measure 0 volts.

 

[rjenkinsgb]

I measured the voltage regulator like you asked, provided a picture.

The regulator is either dead or shorted. If it were shorted, it would be hot.. Most likely just a random failure.

They are readily available from electronics suppliers or ebay etc.

10pcs SMD HT7133A-1 SOT-89 HT7133 7133-1 Voltage Regulator | eBay

We will leave it for everyone that leaves it for us.

www.ebay.co.uk

 

[halleffector]

The regulator is either dead or shorted. If it were shorted, it would be hot.. Most likely just a random failure.

They are readily available from electronics suppliers or ebay etc.

10pcs SMD HT7133A-1 SOT-89 HT7133 7133-1 Voltage Regulator | eBay

We will leave it for everyone that leaves it for us.

www.ebay.co.uk

Thank you so much!

Is there any reason to suspect that the switch is also broken? Is there any way to test it?

 

[rjenkinsgb]

Is there any way to test it?

Only once it has the correct supply voltage again.