Now the LED is lit and the amp works fine. it does look like the D1 LED on the B board illuminates more from the bottom than the top, so maybe i missed it initially in a room with more light?
I guess i'll monitor the amp and see if the left channel drops out again. Both times(left channel not working/amp working) the amp had just been turned on so it doesn't seem like a bad solder joint heating up and failing or filling properly and working.
voltages
1: 73.7
2: 182.6
3: 0
4: 182
5: 71.5
6: 0
7: 104.2
8: 0
9: 103.2
10: 0
11: 0
12: 0
13: 181
14: 0
15: 201
20: 0
21: 220