Get a $5 desoldering pump. Heat solder for battery terminals with new solder to get flowing. Use pump to draw old solder out. Repeat for all 6 terminal contact points. When clean, carefully but firmly start juggling the battery holder loose making sure there is no residual solder connecting to the trace. Install new $3 battery holder, install batteries. No more adjust failure. If you want a ghetto fix, a clean penny placed on the battery terminal for the broken terminal can work temporarily.