How to repair this failed induction cooker?
My induction hob failed while in use. It blew the circuit breaker, and since then it blows the breaker immediately on being plugged back into the power.
The ventilation to its underside was not good, so I think that overheating might have caused the failure.
Inside, there's a main PCB, a control/display PCB, a fan, and the induction coil assembly. There is no "hard" power switch - it's all controlled by the capacitative touch-buttons.
The coil measures 0 Ohms (I think that's probably normal), and the assembly has two sensors in the centre - one is a temperature sensor (green wires), I'm not certain about the other. Possibly to detect that an induction-capable pot is on the cooker?
The main PCB is physically divided into the low-voltage control electronics, and the high-voltage coil supply.
When I disconnect the induction coil from the terminals, the device no longer causes the fuse to blow, and the display lights up normally, so I think the fault is somewhere in the supply to the coil. That supply contains some large capacitors and a couple of large transistors (the heatsink has been removed from those in the above photo).
None of these devices look damaged, and the solder joints and PCB traces all look fine.
Can anyone help me work out where the fault lies? My multimeter measures about 600V AC across the open coil terminals when the stove is switched on. But with the coil connected, the fuse/circuit breaker blows before I even have the chance to switch it on. I think there is a relay on board (I hear it switching when I plug it in) - maybe the black device at the top right? Maybe the control electronics use it to switch the coil supply on?
I'm removing some of the components from the board, so I can test them and hopefully find what's broken. The two components that were attached to the heatsink are:
- D25SB100 - apparently a glass passivated bridge recitifier.
- IHW20N120R3, a Reverse conducting IGBT with monolithic body diode.
Hidden below the IGBT is a component which I think must be a thermistor (covered in white (thermal?) goop on the left).
I tried to remove a capacitor to test, but it's not only soldered in, but the terminals also seem to be riveted through the holes in the PCB.
Anyone got any ideas which components are most likely to have failed, so which to look at first?