Dimmer repair

Hi Walid,

If you only have off and on and when the dimmer is in the on position it is always at full brightness then the most likely problem is the Triac. You can test this with a continuity tester when the dimmer is removed from power by checking the continuity between A1 and A2 terminals. It should be open under normal circumstances. If it is shorted then the triac is bad. The other components are probably OK. The BTB 04-600A is a 4 Amp 600 Volt triac and can be replaced with pretty much any triac that has ratings of more than 4 amps and 600 volts. I have some BTB 06-600 which would be 6 amps and 600 volts. If you are inside the USA I will send one to you. If you are looking at the triac with the pins down and the label facing you the A1 and A2 terminal are the left pin and the center pin. The right pin is the gate and should be attached to a DB3 trigger diode if you have a standard design.

John

Hi John,

Thank you for your help I really appreciate your kind answer but I am too far from you that would make this triac very expensive So, I am experiencing exactly what you described and already replaced the old triac with a new one labeled BTB08-600BW (the only "equivalent" triac I found in the neiborhood) which didn'ty solve the problem. So I just tested both of them and both of their A1 and A2 show no continuity....does that mean they're both open and ok ? When I tested the capacitor I got a 0.0µF instead of 0.033µF...is it possible that my tester is not sensitive enough or is my capacitor is dead ? In that case could he be the origin of the problem ?

Best regards,

W

That knob is also used to go from OFF to min light, at that point (even when in off position) it reads 14.6 when DMM is in 20 Kohm and when max bright light it reads 1.8 when DMM is in 200 ohm.

See if you can remove the solder from one leg of the control so that it is separated from the circuit trace. Try the dimmer with power on. The light should stay off. Unplug the unit and check the resistance of the control again with the one leg still detached. When you read the meter watch to see if a "K" is displayed with the number on the display. What are the minimum and maximum position resistances?

John

Hi John, I "drew" the circuit of the dimmer. Here the control is labeled P and has 3 legs: 2 that you can see on the other photos and one under it. Please let me know which one I should remove the solder from.

Walid, can you double-check the circuit around the potentiometer P and R1?

On your circuit that looks like a dead end. It only has one wire connected to the circuit.

Hi Jan, sorry I indeed forgot some part of the circuit but it doesn't involve the paret you pointed. Here is a corrected drawing and the photo of the back circuit annotated.

My mistake, phase in is lower. Here is corrected:

Hi Walid,

The two connections at the center of the board are the ON OFF switch . If you can remove the solder from either of the other connections at the edge of the board so that the metal leg from the P control no longer touches the copper you will be able to perform my experiment. Nice job on drawing the schematic. I am not sure that it is totally correct as the switch isn't where I would expect to see it in the circuit but who knows. This experiment is to verify that the control is working properly. Once the leg of P is no longer touching the circuit copper traces you will have to touch the meter to the two legs to get the resistance readings.

John

Thank you John. Am I supposed to test it while light is at max light or dim ?

We need to get a resistance reading on the two legs closest to the edge of the board in the dim position and the bright position. Make certain there is no power to the system when these readings are made or you may damage the meter.

The holes are too narrow the legs are still touching the pcb...I am going to take it away and test it away from the circuit is that still ok ?

The holes are too narrow the legs are still touching the pcb...I am going to take it away and test it away from the circuit is that still ok ?

Sure that will work.

I have to leave for a while. I will check back in a couple hours.

John

Okay, here are the mesures:

Max light: 1.7 when DMM is on 200 ohm

Min light: 16.8 when DMM is on 20 Kohm

OFF: oscilating between 16.8 and 17.5 when DMM is on 20 Kohm

My first question is: Did this dimmer ever work to your knowledge?

Your readings on the variable resistor are 20 times smaller than what I would expect them to be in this design. Is it possible that this unit is a manufacturing defect where they accidentally installed a 20K variable control when they intended to install a 400K?

Do you happen to have a high ohm potentiometer like a 500 K that we could patch into the circuit to see if we can get it to dim. If you have such a potentiometer let me know and i will tell you how to patch it in to verify this theory. As i am sure you already know you have to be careful as we are dealing with hazardous and possibly fatal voltage levels in this circuit.

By the way your excellent technical skills have made this troubleshooting adventure a lot of fun.

John

Thank you John I remember it working perfectly yes. When you asked about the 500K potentiometer, I remember seeing this on the one installed : B500K

This can't only be a coincidence right ? So how this could be malfunctionning ?

Great sleuthing, John. +- 17K for a 500K potentiometer is indeed off.

Walid, the potentiometer upper housing and shaft are plastic for your safety - it's wired to your power outlet without isolation.

I'd advise to use an equally well isolated one, if you are going to replace it.

I started to look for an equivalent on the internet...most of the ones I saw have 3 front legs :/

Just out of curiosity, isn't it possible to fix it ? Or at least to try to understand what happened to it?

For your information, as a novice, I certainly tried an economic bulb at some point...

It is very very unusual for a control to change value. I have seen situations where too much current has damaged and changed controls but usually the resistance goes up and not down. If the control had some sort of contaminate that was an electrolyte spilled on it the resistance might come down. If you can find a replacement, which may be a challenge, you could raise the metal tabs on the body and open the control up to see if anything internally is evident. By the way you can turn any of the three legged potentiometers into a two legged one by cutting off one lead.

John

It seems that this one would do the job :

https://www.amazon.fr/gp/product/B07MLFX3Y4/ref=ox_sc_act_title_1?smid=A38WCF64ZZVDKC&psc=1

Now I will begin the disassembly to to take a look inside and will get back to you.

I just thought of another possibility. It is possible that the wiper inside the control has come loose from the shaft and has limited mobility near the low end. Bend the metal tabs up and open the control and check it out. You can also test the carbon strip by putting your meter from one end to the other. I bet we will see 500K or there abouts. If the wiper is loose perhaps you can fix the control by reattaching it.

John