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Introduction

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.

https://www.philips.de/c-p/BTM2310_12/mi...

  1. Remove screws Remove screws Remove screws
    • Remove screws

  2. Open tray and unclip front of tray There are two hooks and some glue Close tray
    • Open tray and unclip front of tray

    • There are two hooks and some glue

    • Close tray

    • Remove screws for front

    • Remove front

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  4. Remove screws
    • Remove screws

    • Remove PCB from front

  5. 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. 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. Remove ribbon cable
    • 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.

    • 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.

    • Remove ribbon cable

    • Measure resistance to ground at this point. Should be OL (open)

    • If not, measure resistance across pushbuttons. Search for lowest resistance. This is the place you want to replace the pushbutton

    • The resistances (in the circles) from left to right are 1k, 1k2, 1k8, 1k8, 2k7, 4k7

  6. Remove pushbutton and either clean it, or replace it.
    • Remove pushbutton and either clean it, or replace it.

    • I did not find a way to open and reseal a button, so instead ordered replacement buttons. They are very cheap.

Conclusion

To reassemble your device, follow these instructions in reverse order.

Thomas Widmaier

Member since: 03/05/2013

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