I purchased 1 month ago 2 second hand S9. One work perfectly but on the second, the chain #7 is not displayed in the interface:
https://i.imgur.com/a5uuHfC.png.
It's not displayed on the miner status because it's powred off by miner.
driver-btm-c5.c:13421:bitmain_c5_init: Chain[J7] has 0 asic
In plain English, this is a dead hashboard, the S9 you bought could be 4 years old and has not rested expected for the shipping duration to your address, it's perfectly normal for it to lose a board or two, and 90% of the time it starts with the middle board exactly like how your miner did, the middle board doesn't have the best air-flow due to the fan motor, that's why some people like phill use a spacer to allow more cooling.
You could try the basic PSU / ribbon cables switching but chances are, it's a dead hashboard just leave it there and mine with the other 2 boards.
