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An inverter (or dimmer) can modulate the intensity of a lamp to provide a pleasant atmosphere. In case of breakdown, several tracks are to be searched...

Text and photos C. Petitjean

Practical advice

Respect the broaching of the triac, without inverting it.
If you can not get the component's original reference, just choose an equivalent. What matters is its amperage of 6, 8 or 10 A and its reverse voltage: 400 or 600 V. When welding, do not overheat with too powerful iron. You risk damaging the new triac or taking off the tracks from the circuit board.

To troubleshoot a fixture, you first need to check some simple items, starting with the light bulb, but also the power cord and fuse inside the dimmer. After these checks, if the light still refuses to shine, there is a good chance that the electronic component of the system (the triac) will be damaged. A new drive costs only a few euros in supermarkets. But if no model available suits you (shape, power...), it is not very difficult to repair it.

Operation

The 230 V AC that powers all our electrical devices has a frequency of 50 hertz (the current oscillates between positive and negative alternation fifty times per second). in the absence of a dimmer, the maximum power is transmitted to the bulb at each cycle.
● The inverter is used to modulate the energy thus transmitted. It consists of an electronic component - the triac - with three electrodes: two anodes and a trigger (see photo 6). The triac is associated with a phase-shifter that delivers pulses to "trigger" the passage of the current supplying the bulb. The phase shifter is controlled by a potentiometer. Each position of the latter induces a "delay" in the passage of one or the other alternation of the current (+ or -), which results in a variation of the luminous intensity.

Troubleshooting

The first step is to test and eventually replace the defective elements, starting with the plug (plug) to get to the lamp. These checks are obviously carried out on the disconnected luminaire of the sector!
● To check the power cord, disconnect the two wires at the input terminal of the drive and connect them together (closed circuit). Connect an ohmmeter to the two pins on the plug: it should read "0" ohms. If it displays "∞" (infinity), it means that the thread is interrupted. It is then necessary to replace the cord.
● If unsuccessful, check the circuit board fuse. Pull it out of its slot and test it in the same way as the power cable by applying a tip of the ohmmeter at each end. If necessary, replace it imperatively with an element of the same intensity (often four or five amperes).
● After these interventions, if the light still does not come on, the triac is faulty. The coin costs around € 1.5 and its replacement is a little trickier to perform. Desolder the triac of the circuit board using a pump and a soldering iron of 40 W max. Remove it gently. Place the new component, in the same direction as the old one, in the holes left vacant. Weld it on the circuit side, using a tin wire with embedded stripper. The lamp must now light up and its intensity can be modulated at will...

Open the drive housing

Open the drive housing

To open the drive cabinet, remove the potentiometer knob and loosen the two mounting screws. Check the cord and test the circuit board fuse.

Test the fuse

Test the fuse

The fuse is tubular type under glass (5 A). To test for continuity, connect the terminals of the ohmmeter. If the hand indicates "0", it is good. If it says "∞", replace it.

Extract the electronic card

Extract the electronic card

To replace the triac, remove the electronics board from the case. To do this, remove the two cable clamps - mains and lamp side - that hold it.

Remove the fastening rivet

Remove the fastening rivet

Welded vertically on the PCB, the triac is further fixed by a tab on the aluminum radiator which ensures its cooling. Drill and remove the blind fastening rivet.

Weld and vacuum weld

Weld and vacuum weld

On the back of the circuit, on each of the pins of the triac, place "nose to nose" the desoldering pump and the hot iron. As soon as the tin melts, trigger the pump to suck the solder.

Identify the pinouts

Identify the pinouts

To properly identify the broaching of the new triac (and do not weld it upside down), lay it flat. Most of them consist of: from left to right, anode 1, anode 2, trigger.

Replace the component

Replace the component

Replace the new component by inserting the three pins into the dedicated PCB holes. Secure the bracket to the radiator with a Ø 3 mm screw in place of the original rivet.

Solder the pins

Solder the pins

Weld the three triac pins on the copper tracks on the back of the circuit board. Use a tin-removing alloy with a 40-watt iron. Cut the pins flush with the welds.


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