Fixing S9 hash boards is not something that someone can tell you how to do from scratch, it's a long process , unless you have a certain a problem or stuck in one specific part then your question will go unanswered.
For the board shows only a given number of asics, it indicates that one or more chips have gone bad and must be changed, for that, you need to follow the process which is not simple and in many cases you better of just throwing away that board, follow this topic >
https://bitcointalksearch.org/topic/has-anyone-mafe-their-own-probes-to-test-s9-hasboards-how-to-test-5191162I put a link to a YouTube video there, make sure you watch it to get a better understanding, and if you are not good in dealing with electronics, your chances are slim to nothing.
As for the boards that show 0 asics, in many cases it could be a firmware related issue and can easily go away by flashing a different firmware , that one I had the most luck was this version:
Antminer-S9-all-201711171757-autofreq-user-Update2UBI-NF.tar.gz
You can read more about it here >
https://bitcointalksearch.org/topic/m.46000519also , a board that shows 0 asics could be due to one of the following reasons.
1- A failling PSU
2- Bad data cable (hash board to controller)
so make sure you test those as well.