I recently dugout my Tascam 414 MkII from my closet that I got years ago and never properly learned to use. Now that I want to learn to use it I discover that track 4 won't pass any signal, both pre-recorded on tape or live from the mic/line/guitar in. All the other channels seem work fine, but when attempting to record or even just pass signal into the headphones/monitor outs track 4 is dead silent. Recorded something on track 1 to flip the cassette and see if it would play in reverse on track 4 and again, dead silent. When turning up effect 1 while playing the cassette I noticed a 'white noise' present in all but track 4 when the knob was turned up all the way. It also cant have tracks bounced down to it. I have absolutely no knowledge of how to go about fixing this but do have a soldering iron and I would really appreciate some advice on how to go about fixing this. If this is something out of my realm of abilities would I appreciate being pointed to someone who would be able to fix it.