The only alternative to changing the whole strip is component level troubleshooting and repair. In a situation where you would be paying someone to fix it, likely it would be cheaper to swap the whole card.
Still, it might be worth looking for:
* Bad electrolytic capacitors. These are the component most likely to fail since they degrade with age/use. Sometimes they bulge or leak when they fail, but not always.
* A cracked or otherwise bad solder joint. Visually inspect the bad channel and compare with one of the good ones. If you find a cracked solder joint then someone with basic soldering skills could fix that.
If the picture you posted is the actual circuit card, and the bad channel is channel 1, then you might want to look at what the black speck is between R73 and R80.