Ceramic Cooktop Switch - EK755 - Failed touchless switch

[fabfab]

Hi.

I need a little help. My Ceramic Cooktop Siemens EK 755 has a 'touchless' switch to switch on the outer / bigger heating element for bigger pots and pans.
You touch the glass and below the glass there is the switch.

The problem - it does not work anymore. I replaced it with the second one > Everything works fine. So its definitly the switch 75.12000.153 62791002 62662003.

I have litte understanding which component could have failed,  but are able to replace them.
Do you have a clue, which component has failed?

I attached a pictures of the switch and the heatmark. I forgot to make a picture of the second backside where the relay (between 4 and 4a) is.

Can you give me a hint, where to start looking / what to replace?

Thank you very much for your expert advice.

[fzabkar]

Is there a 1uF 250VAC film capacitor underneath the larger PCB? I'm expecting to see a transformerless supply for the IC on the switch/lamp PCB.

The pinout of the ribbon cable seems to be as follows:

relay drive output from SOIC-8 IC
DC positive
lamp supply positive
DC negative

The burnt (?) component appears to be a zener diode which sets the supply voltage for the IC. It would be part of the transformerless supply. It often goes short circuit in this topology.

[fabfab]

Dear fzabkar,

thank you for your answer. I currently don't have the possibility to make more pictures.
Do you think it is worth/possible to replace the ZenerDiode? Or did the short circuit do more damage?
What kind of Zener Diode would I need?

Thank you

[fzabkar]

Measure the voltage between DC positive and DC negative at the ribbon connector on the working unit. That will be the voltage of the zener diode.

[fzabkar]

This is the kind of transformerless circuit you should expect to see on the other side of your PCB:

https://www.eevblog.com/forum/repair/coffee-grinder-failing-motor-ok-but-electronics/?action=dlattach;attach=1440436;image