The duck repair

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For some time now, the thermometer I have at my desk, a play-toy bath-duck with build-in thermometer, have been faulty. It can still go QUACK QUACK QUACK when activated, but the display with the temperature (it has a sensor pointing downwards, to measure the temperature of the bath-water) has shown nothing at all. Time to change that.


Taking it apart showed a possible reason for the fault: pcb had some white powder-like substance on it, crossing tracks. I believe it to be causing high-ohm connections where there should be done.

It was cleaned off and I sat back with a mystery on my hands: The display. The LCD element had no pins or pads. The rear-side had a pure white surface of witch I could not measure any resistance on, was searching for a similar pattern of pads like the ones on the pcb, but there was nothing. It is clear, that no matter how it works, the needs to have the pads on the PCB in close contact with the LCD element in order to work, as the screws connecting the pcb to the LCD/plastic frame, holds it firmly in place. As seen on the pictures, the IC used for buttons and drive of LCD, is one of those integrated with the PCB, widely used in calculators. The hole circuit is run of a 1.5V AAA cell so no heavy induction or huge static fields are involved in the transfer, yet I do still suspect some kind of static field used.

Further research on this type of connection needs to be done, once CBA allows it.

Notice the 26.2°C reading on the duck, caused by me fondling it....


[20:05] <nomead_> LCD with no pins = probably uses conductive rubber, "zebra rubber"

[20:06] <nomead_> the two rectangular rubber bits seen in bild2335, have stripes, alternating grey (non-conductive) and black (conductive)

[20:06] <nomead_> or is the other one just foam rubber

[20:08] <nomead_> and you really can't see the "pads" on the LCD glass, well you can if you're very careful. it's just a thin metallized layer on the glass, it reflects light slightly differently on those pads...

[20:09] <Jan_Goofy> hmm are you saying it is the thin black rubber at the top?

[20:09] <Jan_Goofy> that makes the connection.

[20:09] <nomead_> yes.

[20:09] <Jan_Goofy> ah, yes now I see it.

[20:09] <Jan_Goofy> the other one, the big one, is just a foam-thingy.


--Jan Goofy