HP Printer (Deskjet 6840) PhotoInterrupter fix

[Rentium]

Hi!

This is my first topic and i'm not sure where i should post it, it's a fix, but it's also a newbie question so i figured this is the right place.

My printer recently suffered a common problem where the lever that detects the main cover position broke off and makes it impossible to print anything since it's stuck in the open position.
I have little knowledge about the operation of a photo-interrupter and i'm wondering if i can replace it easily soldering a few wires and a manual external on-off switch that i can use to send the "cover open" or "cover closed" signal to the processor so i can send the closed cover signal to print or the open cover signal to change the cartridges (They get locked if the processor thinks the cover is closed).

I read a few common photo-interrupters datasheets and my conclusion was that the output was 0V for low logic signal and 5V for high logic signal however i'm not sure if (and how) i can simulate that with a on-off switch.


Here´s a link to a imgurl album with a few pics of the photo-interrupter.
http://imgur.com/a/ageZE


Thanks in advance,
Rentium.

[SL4P]

Test your problem by putting a piece of opaque cardboard or plastic in the slot/gap of the opto (photo interrupter).
that will stop light getting from the emitter to the detector - telling the printer the (broken/missing) lever is back in place.
The material you use should be opaque to IR, and make sure to completely blocki the optical path. |Ou

[Rentium]

Thanks, the opto is operating correctly and i can tell the printer the lid is closed or open by blocking/unblocking the path just like you said, the problem lies on a lever that just broke off and seems like a common fault in this model: http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01065334&cc=us&lc=en&dlc=en&product=385458 .

The lever is broken in a way that i can't put it back together and the opto is located deep inside the printer, that makes it very hard to try and fix the (odd shaped) lever hence i wondered if i can replace it with an external switch and operate it manually when needed.

Thanks again,
Rentium.

[SL4P]

Yes - you could replace the opto with a switch -- at least that lets you 'return the cartridges to the centre when you want to load/change them.

In the attached image - you basically want to put a switch in place of the RHS of the opto.
If you decide leave the opto in circuit on the board (no issue yes or no) - then you must block the IR light path, or the switch is effectively <always> closed - because the LEDs light can always reach the photo-transistor

[Rentium]

Like you said, I soldered two wires and a switch ( A desk lamp switch ) across RHS , covered the sensor with a piece of cardboard and insulating tape and voilá  works perfectly, Thanks   

.

? Thanks to you.

[SL4P]

Very glamorous!