Step 1: Place parboiled chicken bones in a pot, with the yam, carrot and ginger. Add water, enough to just immerse the chicken.
Step 2: Turn on heat and boil. When boiling, turn to lower heat and simmer for about 20-30 minutes till yam and carrots turn tender.
Step 3: Can add some mushrooms at this point. Salt to taste, then turn off heat, cover the pot.