Michael, soldering approaches being an art form. To do it correctly w/o making the damage you're trying to fix worse, requires a lot of patience. The coating is there to seal the pc board traces from moisture and corrosion. There are a couple of ways to remove this coating. Least destructive is to use q-tips dipped in acetone or laquer thinner and rub the areas you want to wwork with. The least desirable way is to sure a sharp object and scrape the coating off. But,, on a cruise amp board, you will be doing a lot of scraping. Don't overheat the traces, or they will lift off of the fiberglass substrate. Be careful and you will be able to get this job done..

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.