Buttons all do the wrong thing- ever seen this?

[Skippy]

I'm trying to fix a CD player/amplifier combo. The problem I've got is that there are a series of buttons on the front, but all of the buttons do the wrong thing. The CD eject button doesn't eject the CD, but the skip track buttons do, and so on.

The board the switches are on has several switches, but only 3 wires coming out of it attaching to the main board. and the switches are attached using a series of resistors, so I guess the board works out which button is being pressed by the total resistance on the two wires.

I've replaced the board with another one that I know is good in another identical model, but it still has the same problem.

Has anyone ever seen anything like this?

[Simon]

seems to be a problem in the unit then that is misinterpreting the button signals. What is the button board connected to ? could be that some parts on the mainboard have failed and it's mis interpreting the buttons, or you can work out the new sequence and try and sort out the buttons - have fun

[firewalker]

I had a similar problem with an LG monitor. It was using a method for many button but a minimum I/O usage. On the button pcb there was couple diodes and resistors. One of the diodes and a resistor was bad and causing similar problem to yours.

Alexander.

[ivan747]

If it decodes buttons by reading an analog voltage, you can check the voltage on the ADC's voltage reference.

[David_AVD]

Normally a fault like this is the buttons being worn out and having a higher than normal ON resistance.  Since you substituted another (known good) board it sounds like you can rule the button board out.

Look for dry joints on the main board or perhaps glue that has gone conductive.  Perhaps even a leaky capacitor around the key scan inputs of the micro.

[poptones]

I had a VCR that did this after a nearby lightning strike. It still appeared to "work" it just went insane.

[Jad.z]

I'd say it's the voltage that is feeding the resistive divider that went off. You might want to check it and compare it with that of a working unit.