OK, I'm over being mad at AK for eating a post, and will replace my rant with more or less what was eaten. I'll save a copy BEFORE hitting save, that's for sure!
My next suggestions are somewhat riskier in that they will involve shorting together L & R signal points in the interior of the tuner board. It's still completely safe as long as all goes well, it's just easier to make a slip when working in the interior.
First, short together the terminals of R46 and R47 that are nearest to the low-pass filter (F4, a large-ish rectangular block). These are the output points of the LPF, so if you now get sound in both channels, it means the problem is in the LPF or before it. If you DON'T get sound in both channels at this point, don't proceed with the next suggestion.
Next, short together the terminals of R33 and R34 that are nearest to Q6, the PA1001 chip. These are the input points of the LPF, so if you now get sound in both channels, the problem is before the LPF, perhaps something wrong with the PA1001. My hunch is that you'll only get sound in one channel at this step, which would tell us that the LPF is bad. That would not be good news, since I'm not sure how you could fix that, but better to know than not know.
chazix