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Looking for answers to the problem of a randomly opening CD-tray on Philips equipment, I also tried the several times described fix on the open/close switch. But the switch was fine. So digging deeper I discovered the interresting way of encoding different pushbuttons used in this device and the problems that arise with it.
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Open tray and unclip front of tray
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There are two hooks and some glue
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Close tray
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Remove screws for front
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Remove front
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Remove screws
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Remove PCB from front
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This is the section of the pushbuttons. Each of them, when pressed, is shorting to ground one connection in a resistor chain. This basically is a variable resistor to the microcontroller on the other end of the ribbon cable. The microcontroller measures the resistance and decides which value means which keypress.
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The problem comes when there is another resistance appearing due to dirt or other reasons. Then the whole circuit can behave as if random keys are pressed.
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Remove ribbon cable
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Measure resistance to ground at this point. Should be OL (open)
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If not, measure resistance across pushbuttons. Search for lowest resistance. This is the place you want to replace the pushbutton
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The resistances (in the circles) from left to right are 1k, 1k2, 1k8, 1k8, 2k7, 4k7
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Remove pushbutton and either clean it, or replace it.
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I did not find a way to open and reseal a button, so instead ordered replacement buttons. They are very cheap.
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To reassemble your device, follow these instructions in reverse order.
To reassemble your device, follow these instructions in reverse order.
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