Because the VT oscillation frequency in the audio range, if not to hear from strong gradually oscillation sounds weak, the DC inverter does not work. Usually battery capacity lack, bad K1, K2 is not open, R1, L1, L2 welding, C1, VT open circuit failure or breakdown of leakage. VT available beta = 100 ~ 120 2SD2060, 2SD1162, 2SC2500 replacement. T1 can use the original core according to the original wire diameter and number of turns rewind, also available to ordinary transistor radios and small output transformer winding: L1, 0.3mm enameled wire winding 20 turns, L2 around 15 turns, L3 ¡Ó 0.08 enameled wire winding 1500 turns.36uservice manual download site