Introduction
My milk frother was defective, the foam whisk turned continuously and with little force. Here are the instructions on how to test the circuit board and which transistor had to be replaced in my case.
What you need
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Step 1 Milk frother Ambiano (Aldi) disassembly
Careful: steps 1-5 are sourced from a guide that's marked as in-progress.
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Under each of the (glued on) feet of the milk frother is a screw (3x13 mm), which has to be removed.
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This is the inside of the milk frother. You can see the main circuit board and a vertical PCB with the buttons mounted on it.
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Here's a short explanation of the connections. All connectors circled in the same color are connected. The L and N wires coming from the lid are routed through the black base plat (strain relief?):
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Red: L wire from power source, connects lid to circuit board
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Blue: N wire from power source, connects lid to circuit board and heating coil
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Green: L wire from heating coil, connects relay on circuit board (marked "heat") to the heating coil
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Both screws on the circuit board (3x8 mm) need to be loosed and all plugs disconnected. Afterwards the main PCB can be removed.
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This is the view after removing the main PCB. By removing the 3 screws you can remove the motor and temperature probe.
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It's better to remove the motor as is and not disassemble it any further, so as not to negatively impact the water resistance.
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Don't forget to apply thermal paste to the temperature probe during reassembly.
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Remove the PCB with the buttons gently from the clips.
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The main PCB is is divided into three sections
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AC 230 V (red)
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Rectified alternating current (blue) "behind" BR1, about 450 V
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DC section (green), probably 12 - 20 V for the motor and 5 V for the microcontroller
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If you have little experience with electrical engineering don't touch the first two sections. You can check the controller function if you apply a voltage "behind" D8 using a lab power supply. More info on that in the second guide on the milk frother.
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Error pattern: As soon as the milk frother is supplied with voltage, the motor starts to rotate slowly. Because of this, the power of the motor is insufficient to froth the milk. The problem was transistor Q3, which is used by the microcontroller to control the motor.
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You can now start the troubleshooting. To do this, supply the DC part of the circuit externally, e.g. by soldering cable ends to D8 (in the picture on the left side of the diode) and to ground (in the picture at the very bottom left of the board) and a laboratory power supply. I have always used 20V.
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If you remove the motor, the NTC, and the pushbuttons and connect them to the board, you will be able to test them. Depending on the foam level, a PWM signal with duty cycle 1/3, 2/3, or 1 must be present at Q3 (pin at the top left of the picture). In addition, the relay should click once when a program is "started" (unless you select cold milk).
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It is a bipolar transistor with 500 ohm series resistor, which type it is exactly I could not find out. I replaced it with a FMMT 618, which is working fine so far.
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Next time I would rather replace it with a FMMT 619, because it can handle more voltage between collector and emitter (50V instead of 20V, judging by the electrolytic capacitors 25V would be necessary for safety) and still can handle a continuous current of 2A - the motor shouldn't really need more.
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If you are missing a power supply tester and the error pattern fits, then you can simply replace the transistor on suspicion.
If you are missing a power supply tester and the error pattern fits, then you can simply replace the transistor on suspicion.
Cancel: I did not complete this guide.
One other person completed this guide.
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2 Comments
Nice, :) I have older or newer model with Resistor (functioning as Fuse) F1 burned will check what is it connected to, probably heating and or other generally AC supplied parts… and power supply to rectifying bridge and further. Pity I can not attach a picture of board.
The company to prevent repairs did clamp slide connectors this much that it was easier to tear out them from PCB than disconnect. Shame of them.
Anyway I am close now to start diagnose/troubleshooting, but searched long time and did not find D8 on your board, nor on my.
It looks very similar, with different shape and positions of the same elements.
