Fully Controlled Rectifier Firing Mode

Hello guys

I have a Miller Big Blue engine driven welder that has a three phase fully controlled bridge with six thyristors. The scr firing module is not working, there is ac voltage of 50v at the input but no output. Looking online I found a universal three phase firing board (model FC36M by United Automation), so I'm thinking of using this board but it has too many setting, I figured everything out but I'm struggling with the firing mode. There are two modes, phase angle and bust fire. I did a little research and I understand what those modes are, but I couldn't find anywhere what mode is used for simple ac rectification. The modes depends on the type of the load, so what kind of load is welding? Resistive? What type of firing mode should I choose?

I am doing this work for a client so I want to be sure that the board is suitable before ordering or else I pay for it, if anyone have the knowledge and willing to help in deciding if it is suitable or not, I can provide more information.

thanks.