I tried a few things with my 2nd hand S1.
Simplest fix, which will get you 2/3 boards mining, is to
- switch it all off
- disconnect 12V lines from the faulty board
- check that there are no loose live ends in a bad place
- power it up
- mine with the remaining 'good' ASIC boards

Antminer products appear to be safe to run with less than all boards powered.  Think of all that electricity which you are saving by mining at 2/3 speed.
You might also want to look at the "overclocking" method to decrease (rather than increase) clock rates.  There can be times when decreasing the clock rate by about 10% does restore operation of the bad board.