Smeg MP66322X Microwave oven

[Dapman]

Hi I have an unusual fault on this microwave.When operated there is no supply to the transformer,more precisely there is no neutral which originates from pcb board.I have changed the board but have same problem,i have checked all tocs and checked insulation before fitting board HELP!

[electrofix]

check the door microswitches are all operating correctly

Dave

[Dapman]

Hi Yes checked door switches,the stirrer fan motor also uses the same supply as the transformer and thus does not work,there is a live supply but no neutral.
There is no neutral at the pcb,i was thinking it may be a fault with the facia pcb but it counts down and the blower motor starts up.

[electrofix]

when you say there is no neutral at the pcb I assume you mean the relay on the pcb does not close to supply it as it would not power up without it. have you checked for bad relay joints ?

could just be a faulty relay, try giving it a jolt with a screw driver while unplugged.
you could try to measure the voltages to the relay coil whilst it operates

I would suggest you isolate the transformer until you know whats wrong, saves having to keep water in the unit and stops HV circuits
also you say model is MP66322X I found MP6322X so I am assuming the extra 6 is an error

Dave

[Dapman]

Hi My mistake you have the correct model,the pcb board is a new part and yes i have disconnected the supply to the transformer for safety.
The ribbon cable connecting the two boards is only three conductors two of which would be needed to power the facia pcb.

[electrofix]

ah see you have changed the board sort of missed that first time

just though I would check you have been sold correct part no 811652128

cant see the front board being at fault but you can never be certain. little or no tech for smeg around

just a thought its not in shop demo mode is it ?

Dave

[Dapman]

Hi Thanks for all your help you hit the nail on the head,it was in demo mode, unlike a audio system there was no indication on the display.This begs the question did the customer engage by accident which would be difficult or is the history of the microwave different from what they led me to believe.Once again thanks for your help it is appreciated.
Regards Dave.

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