It sounds like your problem may be different if you are reading 12V at the big connectors. Do you have any orange lights on your power supply? I suggest swapping power supplies to rule that out as a possibility. If you take the retaining screws out from the back of the terraminer and depress the release clip they slide right out. Just switch the 2 you have and see what happens. If it follows the power supply then that's bad. If not then you have a board problem. I still suggest trying the car battery approach to rule that out as well but it's likely something else failing on the board. Usually catastrophic failures can be spotted visually. Remove the board and carefully inspect all hardware. It's also possible that the board is not detecting the water pumps. You can try swapping the pump cables from the board that works just to see if it will run. DO NOT start mining like this because you will overheat it almost instantly but it will at least help you narrow down the issue.
Let me know how all that works and we'll move on from there.
If you read back a couple of pages to my original post about my TerraMiners, I had already tried all of those things that you mentioned prior to first posting. I read through this thread and tried some of the "quick fixes" first to see if I could narrow down the problem. Both power supplies work fine and are supplying good power to the boards. I tried swapping the power supplies and the problem stayed with the board closest to the power supplies not turning on. I have two solid green lights on the back of each power supply. I tried swapping the pump connectors and couldn't get the board to start up that way either.
Now, on to what I have NOT tried yet since my first post about this due to lack of time: I have not yet tried physically switching the locations of the two boards. I have not even tried removing the bad board to check out underneath it yet. The top of the board looks good though and I can't see anything out of the ordinary. The tops of both boards look identical and nothing seems blown. I haven't tried removing all of the Arctic Silver 5 thermal paste that I slathered on all of the chips yet either. I THOUGHT that stuff was supposed to be non-conductive, but is it possible that the thermal compound could be shorting out one of the chips or something?
For now, I have it running on the one "good" board. The Arctic Silver 5 compound SUCKS @$$ though and I have to run the board at power stepping 7 and I'm only getting about 200-260 GH/s out of it right now. Even if I can't get the bad board to start running again, if I redo the thermal compound on the chips with the Liquid Pro and get it running on one board at 812 GH/s, I'll be happy with that for now, I guess. It's better than nothing and better than what I'm getting out of it now, lol.
Even my other "Miner formerly known as the good TerraMiner" has gone down the drain and I haven't even touched that one. It was running at the full 1,622 GH/s when I first got it and set it up to mine. In less than a month (and dozens of reboots to try to get it to start mining better, which only seemed to result in losing more hashing power each time, which is annoying...) it is now down to barely 1,000 GH/s! (It is currently running at 1,035 GH/s at the time of writing this.) It looks like CTA0 is still running at max capacity as I am getting 811 GH/s out of it, but CTA1 is the problem. It is throttled WAY back to only 220-225 GH/s and it is still running temperatures around 60-75 degrees Celsius. Looks like it is time to redo all of the thermal compound on that machine as well.
I actually just found this post from ck on the matter .. I may give this a shot and see if it does anything. Easy to fall back if needed. I have a node running CKpool on a server in the same rack with these miners so I can easily test it out.
Haha, small world, right? I've been mining on CKPool as well with my miners. It has been pretty decent for me, but the guy who sold me the AntMiner S5 told me to switch to the AntPool for better payouts. He said they don't charge any pool fees, as opposed to CKPool's 0.9% pool fee. IDK, for some reason I still like mining on a smaller pool to help distribute the hashing power of the network more so everyone isn't just mining on the same big pool, but the no fees is definitely a big lure for me...