| Electronics > Repair |
| Diagnosing / repairing Nespresso Vertuo coffee maker. Heater circuit burned. |
| (1/2) > >> |
| xfint34:
I've got a broken Nespresso Vertuo coffee maker that isn't working. It turns on. Tries to enter ready mode. Eventually the indicator LED goes to a solid red ring of death. There is no definitive error for this state. It seems to be a catchall for various different faults based on the problems I've seen online. For the machine I have I've narrowed it to the water heater part. There is a burnt resistor on the power supply board. This traces directly to a triac + optocoupler circuit. I'm not certain what exactly caused the fault though. And if just replacing the optocoupler will fix it. I've attached a schematic I drew of this part of the circuit. The 100 ohm resistor is what burned completely. There is no other visible signs of damage. I believe it is 100ohm based on a not so good photo of the board online. It may be 56 ohm. I'm not sure. I tested the triac using a multimeter based on methods shown on Youtube videos. It seems to be okay. Everything else about the machine works. The MCU is functional. It can enter cleaning mode and activate the water pump. The heater just doesn't heat up. Optocoupler model: FOD4208 Triac model: BTA12-600BW There's a few things I've got questions about. 1. The heating element shows about 11-12 ohm resistance. I think this seems okay? 2. The optocoupler LED shows a diode voltage drop in both directions. Does this mean the diode is bad? I've seen info about shorted or open circuit diodes but nothing about what it means if reads a voltage drop in both directions. It's about 1.1v in forward voltage. And about 0.9v in reverse. The output pins shows open circuit either way I apply a voltage to the LED. 3. What caused the resistor to burn up exactly? I have no clue where it might have shorted. I'm concerned if I replace the optocoupler it'll just burn up again. |
| xfint34:
I forgot about a substantial part of my question. The optocoupler doesn't seem to be a plain optocoupler but some sort of triac driver. I'm testing the output pins by using diode mode on a multimeter. Is this right or do I need to apply some sort of AC circuit with a signal generator or something? |
| inse:
Though it’s not quite clear what the TRIAC driver exactly does, but it shouldn‘t be conductive without activation. Maybe thats why the 100 Ohms resistor was overloaded and burnt up. Is the TRIAC still OK? You can compare the application schematic in the FOD4208 datasheet to your TRIAC and guesstimate the right resistor value. |
| xfint34:
--- Quote from: inse on January 16, 2025, 06:47:58 pm ---Though it’s not quite clear what the TRIAC driver exactly does, but it shouldn‘t be conductive without activation. Maybe thats why the 100 Ohms resistor was overloaded and burnt up. Is the TRIAC still OK? You can compare the application schematic in the FOD4208 datasheet to your TRIAC and guesstimate the right resistor value. --- End quote --- I double checked the triac. It seems to be okay. I use the method linked below with the multimeter method. Not the with the incandescant lamp continuity tester method. https://drive.google.com/file/d/1-VKzJKeScwRpTkyAg3aK-lUJU7S3v2k_/view I put it all back together to checked the input to the triac driver. The MCU is initially driving it high for 2 seconds at roughly 70%-80% duty cycle. Then it sets it to constant high for like 20 seconds. Then it gives up and goes to red ring of death state. I replaced the burned resistor with 100ohm. There isn't any voltage drop across it. Why would it burn? The triac driver datasheet says 3A max. The Triac datasheet is 4A max on the gate pin. Could something happen that cause the triac to draw >3A. So a cascade happened where the resistor hung on for dear life until the triac driver burned? I don't know just thinking out loud. |
| inse:
Maybe the driver died first going low-ohmic and the resistor wasn‘t designed for continuous operation and quit. The heater was probably saved by a clixon switch. What do you think of this theory? |
| Navigation |
| Message Index |
| Next page |