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dks750 - dust on the photos after new PRNU


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Hi! Recently i have a problem with PRNU. Namely,there is a visible dust on the homogeneous smooth surface. After cleaning lenses above light bulb and the mirror and after doing new PRNU the photos are perfectly clear but after several hours the flecks appear again on the photos. When I’ve installed the PRNU I turned off the machine. Today the new PRNU calculation I have to do every day. Can anybody help me to solve my problem?

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Hi Lilly87,

I had few situation like yours and the problem was that angled lens assembly which is inside of LCD block was brushing the home position sensor and this metal and plastic particles from that sensor are getting inside the unit.

The reason why this was happening was because x4 lens assembly which is on big ball bearing moved upward and start to brush the sensor because it was not levelled to its body. Maybe X4 motor axis bushing was damaged and that angled the gear which is driving the X4 lens and complete lens assembly moved upward. Temporary solution was done by moving that sensor upward to avoid new brushing and new particles coming inside.

But first it is necessary to disassemble the unit (like on image bellow), do not unscrew the polariser because then dust will be on the LCD itself (maybe some is already there?), and be careful about position off the top polarizer which is not glued as bottom one.

Anyway it was very messy inside and even ball bearing was completely blocked by the particles.

This is very complicated and sensitive procedure to do and I would not recommend that you do it yourself, this is work for experience technician.

I received one image from one customer which dissemble this unit and as you can see it was very massy situation.

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Regarding the lens motor, find somebody to change the brushes inside off the motor and clean the rotor, that will fix it for some time.

X4 motor issue which I explained earlier did not stopped the motor completely but this dust forming was a sign off the effect which I explained.

So even if you test motor, that does not give you information if the motor axis is angled to the X4 lens, only if it is turning or not.

Only check to see what is going on is to disassemble the unit (as in images in my earlier post), but I will repeat again, it is very delicate procedure.

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