Replacing the TRIAC on the UNI-PAK II Dimmer Pack

This time, I would like to show you a repair case of ELATION/UNI-PAK II dimmer pack.

ELATION / UNI-PAK II Dimmer Pack

This unit was sent to us by a customer for repair because the dimmer could no longer be controlled.
Let’s check the symptoms.
As soon as I plugged the dimmer into a power outlet and connected a light bulb, I could see that it didn’t work.

The light lit up even though the slider is set to 0 as it’s shown in the picture.
Also, even if I move the slider, the light stays lit and the dimmer pack can’t control the dimming level.
As the customer says, the dimmer doesn’t work.

Let’s open the housing and look inside to find out what is wrong.

You can see a three-legged black part in the center. This component is called the TRIAC.
This TRIAC controls the power supplied to the light bulb.

Now I’m going to briefly talk about the TRIAC.
A TRIAC is a semiconductor component which is often used for stopping and passing electricity. This is called ‘switching’.
Switching changes the amount of electric current to control the dimming.
Control the slider on the dimmer pack, then the TRIAC adjusts the amount of electric current accordingly and changes the brightness of the lighting.

Higher amount of electric current → Brighter
Lower amount of electric current → Darker

It is something like this.

Generally, the TRIAC is symbolized by an electronic circuit symbol as shown in the image below, and by inputting the signal into the G terminal, the current flowing from T1 to T2 (T2 to T1) is controlled.

Now that I have briefly explained the TRIAC, let’s check the condition of the TRIAC on this dimmer pack to repair.
Let's measure the conduction of T1 and T2 with an electrical tester.

The electrical tester is displaying 0Ω. Normally, electricity does not flow unless a signal is input to the G terminal, so it should not be 0Ω.
Since the TRIAC on this dimmer pack always conducts electrical currents, the electricity will continue to flow regardless of whether the amount of electricity is controlled or not. Therefore, the light bulb is always lit up.

Now I understand what causes the problem. Let’s replace the TRIAC and see if the problem happens again.
Since T1 and T2 are not conducting any currents in the replaced TRIAC, it is displayed as O.L.

When I plug it into an outlet, the light bulb shuts off properly when the slider is at 0.

Then I move up the slider…

Now it’s lighting up.There is no doubt that the problem was due to the TRIAC.

Now, the repair is done.

When using a dimmer pack, be aware of the maximum output current.
If the output current exceeds the maximum output current (it’s 10A for this UNI-PAK II), the fuse may blow or the dimmer will be uncontrollable due to the broken TRIAC.

Thank you for reading.