Diagnosing / repairing Nespresso Vertuo coffee maker. Heater circuit burned. - Page 1
Forum section: electronics / repair

author: xfint34
author_rank: Contributor
timestamp: January 16, 2025, 05:15:37 pm
content: 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: FOD4208Triac model: BTA12-600BWThere'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.

author: xfint34
author_rank: Contributor
timestamp: January 16, 2025, 05:47:49 pm
content: 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?

author: inse
author_rank: Super Contributor
timestamp: January 16, 2025, 06:47:58 pm
content: 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.

author: xfint34
author_rank: Contributor
timestamp: January 16, 2025, 09:27:43 pm
content: Quote from: inse on January 16, 2025, 06:47:58 pmI 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_/viewI 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.

author: inse
author_rank: Super Contributor
timestamp: January 16, 2025, 09:38:47 pm
content: 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?

author: xfint34
author_rank: Contributor
timestamp: January 17, 2025, 02:01:23 pm
content: Quote from: inse on January 16, 2025, 09:38:47 pmThere's an NTC on the heater block. The machine has a thermal switch in series with the bridge rectifier but it's clipped to the water pump motor.I guess the designers use software to guard for thermal runaway. Which reminded me of the troubleshooting tip I've seen online saying to leave the device off for 15 minutes to cool down. So it seems like this device does have known problematic heater control.

author: xfint34
author_rank: Contributor
timestamp: January 21, 2025, 09:25:58 pm
content: I replaced the TRIAC controller. It was obviously blown too. The bottom of the chip was cracked. I noticed when I desoldered.Anyways. The resistor sparked immediately. The new TRIAC controller maybe toast(?) In hindsight maybe the resistor was too small. I put a 10k ohm and it didn't burn. There is 120V AC across the resistor. Power turns on and off the with same kind of signal I measured from the low side input to the TRIAC controller. So maybe the controller didn't blow...The heater still does not heat up. I think the TRIAC itself is also bad.I guess I should have tried replacing the TRIAC itself as well. It isn't soldered though. They crimped stranded wire to the legs of the TO-220. I don't know what to search for to find these crimp things. The only thing that comes up when I try to search are crimp connectors.What do I search for to find such parts as pictured?

author: inse
author_rank: Super Contributor
timestamp: January 21, 2025, 09:45:20 pm
content: Did you check the FOD4208 datasheet for the resistors yet?10k appears rather high to me.

author: xfint34
author_rank: Contributor
timestamp: January 22, 2025, 12:22:41 am
content: Datasheet uses 360 ohms. Seems rather low? 120V mains voltage that is a lot of current for a common through hole resistor.The datasheet also uses 330 ohm for the other resistor. There is a 4.7k on this machine. So I used 10k because they are some what proportional. Not sure if that rationale makes sense...I discovered two thermal fuses connected to the heater. It takes more disassembly to see. One fuse is connected to the live wire going to the heater. One fuse is on TRIAC pin 2. The latter has been blown so that explains why there's no power to the heating element. I'm 100% sure it wasn't blown before because I tested the TRIAC through the wires connected to these fuses.The insulation on the wire connected to the blown fuse is degraded and cracked open. I'm not certain I damaged it because it looks very crumbly. Not a clean cut like if I nicked it on something. These wires wrap around the heater so maybe it degraded over time. A short through the grounded heater block could explain why that fuse blew.In the mean time had already I snipped off the crimp parts of spade connectors to use to install a new TRIAC. I will have to purchase a new thermal fuse.

author: inse
author_rank: Super Contributor
timestamp: January 22, 2025, 01:06:18 am
content: Please have a look at the BTA12-600 datasheet as well.It needs 50mA gate current to ignite, you will not be able to achieve this with 10k.BTW in case you need to replace the TRIAC. I wouldn’t bother with specific crimp ferrules if you don’t have them around - just solder it and put some heatshrink on

author: xfint34
author_rank: Contributor
timestamp: January 30, 2025, 12:29:04 am
content: I replaced the fuse and the TRIAC. It heats up. The status light goes green.But now the water pump doesn't work anymore. I enter menu mode and try to run the clean cycle like I did before. The status light flashes red. The motor doesn't start.Btw. I kept the 10k resistor.

author: xfint34
author_rank: Contributor
timestamp: January 30, 2025, 08:05:25 pm
content: It's dead. The worst case scenario happened. Water leaked everywhere.I hadn't reassembled it properly so the part that spins the coffee pod was stuck which is why one of the motors didn't spin. Now I thought I had assembled it properly. It pumped very dirty water for a bit and then smoked. I'm pretty sure there was a severe leak inside. It's impossible to open anymore. The motorized lid needs to be open to disassemble. It only powers on to a spinning pump motor even with no water tank. No signs of functionality from the MCU. No way to tell it to open the lid. Most likely the whole mainboard is shot. It sits below the coffee pod chamber with water flowing through it.There's no way to open anymore without doing so destructively. Maybe I'll smash it apart some day to see what's salvageable.

author: shabaz
author_rank: Frequent Contributor
timestamp: January 30, 2025, 09:21:11 pm
content: There's lots of neat bits and pieces inside Nespresso machines. Might be more interesting to you in pieces.By the way, a Nespresso subscription (effectively just a commitment for a regular sum towards Nespresso stuff, i.e. money which you'd be spending regardless, if you're planning on purchasing Nespresso pods for it anyway) will give a 35% discount on a new machine (up to one machine per year). Not sure if this is the case in all regions, but might be worth finding out for your region.