I suspect for whatever reason you're not getting the more than 5V to light the green indicator. The red indicates you're getting 4V P-P or less, that's not what a good Legacy base should be doing.
Just for yucks, disconnect the track signal from the buffer and see what the signal indicator does with the base connected to the buffer. It shouldn't have an effect, but who knows.
The red light is strictly checking the base output, it doesn't have any connection on the output side of the buffer. Since the buffer could be driving any kind of load, it was pretty hard to pick a number for what voltage you should see out. I figured it was more important to know if the base was having an issue as that's far more likely, the buffer is a pretty simple circuit and should be very robust. There's also nothing to adjust, it just does it's job.
