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John Lewis Microwave Overheat

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  • John Lewis Microwave Overheat

    Could anyone shed some light on this problem please? I have a JLBIMW03 built in microwave that seems to switch on and off when the food gets hot and steamy, e.g. cooking peas. I have changed the control board, the magnetron and lastly the thermistor on the magnetron which seemed to be effective for a while which made me think the original was over-reading.
    However, the problem has returned and about 4 minutes in when things steam the oven flicks on and off. The fans seem to be running fine. The unit the oven is in is open-backed but oddly the vents to let air into the oven case are on its sides which don't have much clearance from the unit sides.
    Any ideas?! Bad design? It does seem to be a steam/heat problem because swapping a jug of hot water for cold will make the problem go until heats up.

    Update. Changed the left hand door switch to no avail.
    On a whim I removed the waveguide cover and the oven ran without problems. There were signs of some arcing underneath the cover. After a clean when the cover was refitted the problem returned.
    I replaced the cover for a new one and the problem is less prevalent but I can't trust it to cook anything!
    I'm now wondering if having no waveguide cover meant steam was being removed more effectively and maybe is steam getting into the front panel? After changing the waveguide cover the oven did its flicking on and off act just after it had finished cooking so is not necessarily a problem when microwaving hence the switch panel idea.
    Have spent a lot of money on parts and wondering what to do next! This was an expensive oven and is the second one I've had after shouting at John Lewis after its predecessor blew three magnetrons but is out of warranty.

    Further update. This now looks more like a problem with the controller (power board was changed) and the nature of the problem has changed slightly. The controls and display now go a bit mad (lights flash, display drops out and the fan and light are switched on and off) when is the microwave power is switched off at the end of cooking.
    I'm now wondering if the controller power is being affected by electrical noise or microwaves leaking internally. I ran the oven with the fuse that feeds the transformer/magnetron out and it behaved OK. Anyone seen this?
    Last edited by thinman; 01-06-19, 03:31 PM.

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