Since VT oscillation frequency within the audio range, if heard by the strong oscillation sounds gradually weakened, indicating DC inverter is not working. Usually insufficient battery capacity, K1 bad, K2 is not disconnected, R1, L1, L2 open welding, C1, VT open circuit failure or breakdown caused by leakage. VT available β = 100 ~ 120 of 2SD2060, 2SD1162, 2SC2500, etc. replaced. T1 can use the original core diameter and turns the original rewound, can also be used ordinary small transistor radio output transformer winding: L1 around 20 turns with ∮ 0.3mm wire, L2 15 turns, L3 wire around with ∮ 0.08 1500 turns.xVqservice manual download site