iPod docking station strange issue: auto switching modes

[nobtiba]

Hi all,

My iPod docking station

There is a peculiar issue: the mode switches automatically. Typically, pressing the mode selection button is required to change modes (iPod, FM, etc.). However, the mode changes on its own, even without pressing the button or after removing the entire control unit. It behaves as if I'm pressing the switch button, which still functions properly.

I have tried the following:
1) Connect everything and press the mode selection button: Each click allows me to change the mode, yet it also changes automatically at the same time.
2) Disconnecting the control unit: the mode continues to change automatically. In the image, you'll notice that the connection slot on the motherboard is empty because I have disconnected the control board from it:
View attachment 335435

3) Connect the control unit: However, within the control unit, if you remove either the capacitor 104, the IR receiver, or both, you can still press the button to change the mode. This leaves me unsure about the actual purpose of these components. Additionally, the mode continues to change automatically at the same time.

I suspect there may be an issue with the motherboard. I've checked the pin connections and used a knife to carefully separate them, ensuring no particles or debris are inadvertently bridging the pins where they shouldn't be connected.

More photos of the mother boards:

Does anyone know how to identify and resolve this issue?

 

[Bill_Bright]

Note your 3rd picture above. Can you operate the device while leaving the tops of those membrane switches off as seen in your image?

My thinking is, "maybe" the tension in those membrane switches has become so weak over time, there is not enough tension to fully open the switch immediately after it has been pressed. With it wide open like that, there is no chance it is still making contact. If it does not change modes this way, those membrane switches may be the problem.

And while the contacts look clean, I would take a "clean" pencil eraser to them to ensure no corrosion and contaminants are on them. Then use a soft brush to ensure no eraser crumbs are left behind before reassembly. Using some good electrical contact cleaner on the contacts may help, as well as spraying each connector contact. I recommend using CRC QD Electronic Cleaner or WD-40 Electrical Contact Cleaner. Just ensure every connector is securely fastened when done.

If you still have the problem and you see no other physical evidence of damage (burnt marks, signs of excessive heat, loose/broken connectors) then it is likely another component has failed and without a schematic diagram and proper test equipment, there would be no way to troubleshoot to the affected component. And unless properly labeled (and it looks like some of the ICs are not ) replacement parts might be hard, or impossible to find anyway.

At least the problem appears to be in the docking station and not the player itself.

 

[nobtiba]

Hi Bill_Bright,

Yes, even with the tops of the membrane switches removed, as shown in my image, the device can still operate, and the mode automatically switches by itself. Even when I disconnect this board from the main board, rendering the switches completely useless, the mode switching remains active on the main board. However, I am unsure where and how this occurs.

 

[Bill_Bright]

In that case, assuming you cannot see physical damage to a component, I suspect one of the ICs has failed internally and the firmware code within has become corrupt. And again, without a schematic with test points and part numbers (assuming replacement parts are available), I don't see how you could repair it. IMO, it is time to shop for a new docking station - or at least a nice set of headphones. Sorry.

 

[nobtiba]

Yes, I've already acquired a new docking station that's working very well. However, with the old docking station still around, I'm keen to debug it to understand the issue and identify the problem. Today, I examined the boards again to trace where the two pins connecting to the mode switch lead. I discovered they connect to pin 10 and pin 20 of a 24-pin IC. This IC is unlabeled, so I can only speculate that it's some type of codec IC.

Next to it is a CD3313EO Wuxi I-core SOP-28 Audio Interface IC. Datasheet:

Wuxi I-core Elec CD3313EO Datasheet

CD3313EO Wuxi I-core Elec $0.3225 - SOP-28 Audio Interface ICs ROHS datasheet, price, inventory C3151976

www.lcsc.com

I inspected all the pins of both ICs, ensuring none are accidentally connected to each other. However, I noticed something unusual. When I touch a specific pin, either with a wire or a multimeter test probe, it triggers a mode change as if the switching button is being pressed. If I attach a wire with an open end to this pin, it continuously changes the mode without any further action. I suspect the wire might be acting as an antenna, receiving signals that the IC interprets as a button press. This suggests the IC is overly sensitive to signal changes and lacks a sufficiently high threshold to distinguish between actual signals and noise. Please refer to the video below for more details:

 

[nobtiba]

Does anyone have any suggestions? It's strange that connection point is too sensitive to any wire plug-in, how to prevent it from happening?