52.

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Across
  1. 2. Mad - with small pieces of coal (5)
  2. 6. No top for opening pack reduced with old herb (7)
  3. 9. Rips when one locks with the instrument used for opening? (7)
  4. 12. The preliminary, opening moves put one in jeopardy (7)
  5. 14. Pointless game show host, _ Armstrong (9)
  6. 15. TIE Pointless game?
  7. 16. Choral composition with very small piece for tenor (5)
  8. 20. Children's game with small coloured balls (7)
Down
  1. 1. Compose small pieces for quintets
  2. 3. Colourful little pieces for festive occasions
  3. 4. Game with small insects
  4. 5. BETWEEN Intermediary's game gamble with small gain, ultimately (2-7)
  5. 7. Pointless game, with small pieces for opening moves (7)
  6. 8. Manages to cover up with small pieces of moulding (5)
  7. 10. Cut into small pieces for cubes used by gamblers (4)
  8. 11. Small piece for testing (6)
  9. 13. Good scope for opening moves (6)
  10. 17. TUNE New York opera house with a French piece for opening? (5,4)
  11. 18. Children's game with small labels (4)
  12. 19. Design made with small pieces of coloured stone or glass (6)