If you see any "x" or "-" under the Asic Status on the Miner Status page you may have bad chips.
If you have an S3 and not a S3+ you should check and make sure your frequency is set correctly under the Miner Configuration tab.
If you have a regular S3 and the frequency is set to 225M you should change it to 218.75M
Then click "Save and Apply"
You can test each side of the miner individually to determine which board is faulty. First you should remove the top cover from the miner, there are 5 screws on each side that you will need to take off.
Once the cover is removed you should see a control card with a cable going to each side of the miner. You can run a single blade of the miner without the other, however you must always use the left cable as the right one doesn't allow power to reach the control card by itself.
You can either cross the left cable over to the right as shown here.
Or you can unscrew the 4 screws holding the control board.
And flip the control board around.
You should then be able to login to the miner and view the status page. If one of the boards hashes low then it may need to be replaced.