Opto sensor on Neff S6409 faulty

According to my service manual here is the remedy for your code....
Run Index Test
Check/Replace Mech Opto Sensor, Check Mech Opto Sensor Wiring
Replace Control Computer.
Check magazine motor.
Check cam switch wiring

I think there are opto sensors around the carousel, these may be faulty as the machine needs to know what position its at.

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this is a very fragile part, please replace carefully and clean the opto sensor beside it.

Possible that the INDETECT paper sensor is not working. Sometimes this can be an opto sensor, If so you need to remove and check using a multimeter and replace the component.
It can also be due to a jammed roller, a failed motor drive or a faulty motherboard .

Check SMPS voltages. Check optical coupler. Check SMPS components. It is difficult unless you follow a circuit diagram.

Sometimes replacing opto isolator may solve!

Caution : Do not switch on T V without opto coupler. ( if you remove for checking ) replace with new one as it is difficult check with service test meter.

Check SMPS circuit.
Check for dry capcitors. Replace OPTO coupler in the feed back circuit in SMPS.

Do not switch ON TV without opto coupler fixed in circuit.

SMPS will go out of control and the + DC voltage will raise infinitely and damage the other parts. If transistors used along with the opto coupler, check them for leakage. Replace them. Otherwise the replaced opto coupler may fail again after few days or few hours of TV working.

this is possible but can lead to more frustration. The cd door usually has a plastic tab that depresses on a button or blocks the opto sensor to indicate it is closed. I presume that your cd door is missing this tab or the circuit that activates when the door is closed is faulty. Block the opto sensor manually using paper or keep the button depressed that the door tabe closes on. You will not need anything to keep door closed unless it is reqiured to play the cd then just use a brick

There is an "opto coupler" in the main drive gear unit (right ride of machine) which controls the drive to the toner/dev units. If this (or part of the drive) is faulty it will give this error.

It relates to the transfer belt unit, replace it

The opto coupler is usually related to just the pic starting out small then filling out after warming. The flyback wouldnt stop the power led from coming on unless the HOT shorted but that would blow a fuse. Check your fuses. You can sign up here for free and your solutions are what gives you your ranking on the site. Premium assistance is a service that requires payment, but I am not sure how that works as I try to help people for free on here