Black screen, led 4th and 5th off

Hi, on this imac i have black screen with audio. The second display with a thunderbolt adapter doesn't work, but i don't know if it is a problem of the adapter. On the capacitor near the lvdc cable and on the connector i've the 12v. Where can I search the problem? Thx

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 0
crwdns2934285:0crwdne2934285:0