Aiwa CSD-ED37 boombox

[The Robman]

So my wife picked up a used Aiwa CSD-ED37 boombox (vintage 1999) a while back where one of the CD buttons was broken, so being the engineering sort that I am, I decided to take the thing apart to see if I could fix it. There was one small plastic part that had broken, so I super glued it and now the button works perfectly, except...

The button in question is the Track Down/Tuning Down button, and now it works just fine, but the corresponding Track Up/Tuning Up button also performs the "down" function (rather than the "up" function).

This has me puzzled as to what could cause such a thing. If I remember correctly, it did this before I did the button fix, so I didn't cause it.

Apart from bad programming in the MCU chip, does any body have any idea what might be causing this, and whether it's fixable.

This is what the unit looks like...



I found a schematic here.

I found another schematic here. (The file is a DJVU file, so you'll need this reader to view it).

If you have a paid membership at nodevice.com (which I don't), there is a service manual here.

You can download the regular user manual here.

I notice in the manual that the higher end versions of this boombox come with a remote control, so I wonder if it's possible to hook up an IR receiver to make my unit remote control-able.

[zaphod7501]

The switches are all in a "ladder" arrangement and the CPU is actually measuring the resistance to ground when a button is pressed. It will detect a function command within a small range of resistance readings. If any switch has some leakage, then it can affect all of the others. If any one of the ladder resistors is off value or shorted then it may produce the wrong command.

The schematic shows switches from s601 through s613 but doesn't label them by function. If the problem switch (up) is electrically next to the (down) switch, then the resistor between them could be shorted. The most common failure is a leaky switch, however. (assuming they are physical switches and not contact pads like remote controls use.

You should make sure that all of the switches are free to "click" and you don't have one stuck or jammed down.

My next suggestion would be to get a drop of isopropyl alcohol into each switch and work them several times. A contact cleaner could be used also but the alcohol should be able to just clean them up a bit. Note that any switch could be leaking a bit, just enough to alter the total resistance to ground when another button is pressed.

Trying to measure the resistance is usually futile. The troubleshooting method is generally to start removing switches from the board until the problem clears. Any leaky switch can alter any function. A lower numbered switch can override any higher number. (per the schematic) A higher numbered switch will "generally" not be able to affect a lower number, since it is effectively out of the circuit when the lower numbered switch is pressed.

[The Robman]

Thanks for the feedback Steve, I'll try opening it up again this weekend and either spraying some cleaner into the switches or dropping some alcohol onto them. I'll also see if the PCB is marked so we can see which switches these are.

Just FYI, they are the little self-contained switches rather than the sort of contacts that we have in remote controls.