Smeg door open fault

Re: Smeg door open fault

I spent quite a few hours trying to diagnose the fault without a schematic. The fault was eventually traced to an open circuit via hole on the control panel pcb (the drive to RL7 coil from driver IC).

I feel that manufacturers like Smeg don’t want us to repair things so they don’t supply schematics and they elevate the price of spare parts in order to encourage people to buy something new when something goes wrong. A few years ago I designed TV’s and I recall a service manual was made available which provided schematics, circuit descriptions and diagnostic information (voltages, signals present etc). I feel we haven’t progressed very much and tend to ignore the environmental consequences of a throw away society.

Re: Smeg door open fault

Yes a via is a plated through hole which conducts from one side of the PCB to the other. Whilst you say it shouldn’t happen I am concerned that when the door lock relay is switched off there is an inductive back emf which causes a pulse of current that flows through the protection diodes in the device. Some relays have a built in protection diode but in this case the current flows back to the driver IC hence the PCB track has to handle a short pulse of a higher current than normal. To me it looked like the via and associated track had blown and there was a slight green smudge on the switch that sat above the via. There might be a slight design weakness in terms of the track width and the size of via, but maybe it was just poor plating in the via hole which fused. One final thought is that if a PCB track driving a relay goes open circuit when the relay is turned on the back emf in the absence of a protection diode will be significant which could cause the sort of fusing I noted as the high votage causes a small arc across the break which would account for the green smudge I noticed above it.