The picture:-
You can see the pads with labels like "K7", "K8", "K9" e.t.c. So two related questions are:-
What is the black stuff (it's loosely conductive)?
Can I solder through it (one of the pads is cracked)?
Note. I've seen PCB Crack Repair
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1 Answer
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It's carbon. The buttons should also have some on them, when the button is pressed the carbon on the button contacts the carbon on the circuit board creating a path for current to flow and that's how the switches work. If you damage the carbon the buttons won't work anymore, don't wipe them, try to clean them, get them wet, or try soldering to them. If a trace is cracked you could try soldering in a thin jumper wire to some parts of the trace away from the carbon contacts, but even that will probably be a problem as you don't want the wire going across the top of the board where it would interfere with the buttons.
