Is working in the assembly and disassembly of equipment for a venue used for various occasions, such as musical concerts that may involve singing and drinking, considered a sin, even though my work is limited to assisting with preparations only?

It is not permissible to work in the installation and dismantling of equipment in a place prepared for forbidden acts, such as drinking alcohol and lewd parties, because it involves cooperation in sin. However, if the place is prepared for permissible acts, then working in it is permissible, and if incidental forbidden acts occur that you were not aware of, then there is no sin upon you. "And whoever fears Allah - He will make for him a way out and will provide for him from where he does not expect."