Dimmer circuit - No Triac ? - Blown out it's A__ - Page 1
Forum section: electronics / beginners

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: March 15, 2025, 07:21:02 pm
content: So put a new-old-stock 1980s 600W wall dimmer into a project box last month so it could be used to control various resistive loads like running my 400W space heater @ 200W which it did well for about 12 hours before it blew leaving only a high setting(probably should have ventilated the box, doh!). Next, of course, had to "take it apart" (see picture). All components are unmarked. The diode looking part is in series with a red cap-like looking component(meter shows both tests as caps 50pf anyway you measure them. Dimmer does not have traditional rheostat and triac/diac maybe that other dimmer circuits have, not sure. Power level was controlled by flicking the light switch up and down possibly making contact with the carbon looking long black traces? These black lines were also tested on my component tester, oddly as about a 7uf capacitor. Switch/wall plate assembly was delicate and switch pieces all feel apart into oblivion when disassembled. Have since ordered a $5 1000W dimmer on ebay that works great with space heater.Question of course is how did this circuit work, and can a part or two be replaced/modified to give variable power to my 60W soldering iron? Thank you in advance for taking the time to read and considerNOTE: Better PICTURE attached !!

author: Ian.M
author_rank: Super Contributor
timestamp: March 15, 2025, 07:55:04 pm
content: That's an interesting ceramic substrate hybrid module. I assume the dimmer slider progressively shorted out the printed resistor near the top edge of the substrate to control the firing delay. At max brightness it looks like a switch contact near the middle of the bottom edge copper may bypass the dimmer. This switch may also break the circuit in the off position.The circuit looks fairly conventional. I've hilited the location of the TRIAC die. MT2 goes to the copper tab connected to the inductor, MT1 to the wide strap to the central (silver) metalization on the substrate, and the Gate connection is via the narrow strap from the DIAC to the die passing through the hole in the end of the MT1 strap.Its not really repairable, though if you clip the two straps and remove the blown TRIAC die, you could probably solder an insulated wire to the gate end of the DIAC and bring it out to control an external TRIAC. MT2 is the inductor connection, and MT1 *may* be the red wire, unless the switch disconnects it from the central metalization when off, which would mean you would also need to bring out a wire for MT1, which is likely to be difficult due to clearance issues.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: March 16, 2025, 06:45:13 am
content: Thank you for your very clear explanation! TRIAC is so small I did not even notice it without a package(talk about economy). The original 3-way dimmer only had three leads (maybe MT1, MT2 and trailer for 3-way, not used, and no ground). To use as a plug and play dimmer I scalped a 2 line extension cord leaving neutral uncut, and wired the cut common wire to dimmer's red and blk leads, capped black trailer lead, then boxed it all up.To summarize reuse plan, in my pea brain anyhow-- external TRIAC would be separately heat sunk with jumper leads going from TRIAC end of original DIAC to new gate, jumper inductor/blk lead to M2, and M1 to red lead. Wondering, when I clip the two TRIAC straps can I leave the TRIAC there. To regulate, could a pot somehow be inserted some-wheres? Lastly, can a 2kW TRIAC work with this circuit, even though maybe should derate rebuild to say 400W?Thanks Again!

author: Ian.M
author_rank: Super Contributor
timestamp: March 16, 2025, 09:11:29 am
content: Removing the straps will almost certainly fracture the TRIAC die, so don't leave any loose debris.You can only do that if the red lead has continuity to the center pad (MT1 strap) all the time. If, as I suspect, the switch mechanism disconnects that when off, you wont be able to get at MT1 as adding a wire thick enough to carry the current will foul the switch slider.Personally, I'd write it off and simply get another dimmer, as there is nothing of value left on the board if you cant use the switch/slider.

author: DAVEISGREAT
author_rank: Regular Contributor
timestamp: March 16, 2025, 06:48:11 pm
content: As you suspect, cheapo switch design too. At least we tried - thank you.Found a New 1kW $8 shipped eBay Special. Won't blow it up this time.