i noticed that just the audio lanes have 1 scratch
I´m wondering if these scratches are too deep?
The board will be covered with a thin layer of resin providing a protective coating over the board. This resin coating is there to protect from scratches, moisture, dirt and other contaminants but also to keep oxygen out to prevent oxidation/corrosion. This layer of resin is actually pretty tough and when the resin is scratched, can look pretty bad, but still be doing its job. I'm just saying, scratches in the resin coating tend to look worse than they really are.
If the scratch does go through the resin and then through the trace it obviously, is too deep.
If you have a decent multimeter, you can measure the resistance through the scratch. It should read a "short" or 0Ω. You may have to dig with the sharp meter probes a little to poke through that coating. I recommend trying two component lead points on either side of the scratch, if possible. The lead's conductor underneath is of harder material making the layer of resin easier to poke through with no risk of poking through a trace, creating more problems.
If the meter measures high resistance (indicating an "open") the trace has been cut. It can be repaired, but I recommend having a qualified tech do it. Soldering is a skill and like all skills, needs to be regularly practiced and honed to be consistently good at it. A qualified tech would (should) have such honed skills - not to mention the proper tools.
When done poking holes through the resin coating, and to repair the scratched area, a dab of clear fingernail polish works great to seal the scratch and where you poked through. Just carefully clean the area first with an alcohol pad to remove any skin oils and other contaminants ensuring the polish adheres and seals completely.
Having said all that, I do not believe this scratch is the problem. If the trace was cut, it is more likely the problem would be seen (heard) consistently, not once every few weeks.
