Free Dynamo From Tixa is a side quest in Jagged Alliance 2.
Dynamo is kept locked in a cell in the western side of the prison. The challenge here will of course be reaching him at all, as there is resistance on the upper levels of the prison is heavy.
More info on conquering Tixa see: Tixa
Dynamo is wounded when you see him, and will implore you for first aid. Once it is given, speak to him again and listen to what he has to say, and the quest will be complete.
A mercenary with at least a modest leadership statistic can persuade him to join the squad for $50/day or for free if the first offer is refused.