Repair of Electronic choke for 4'tube light

I tried to repair two electronic chokes for 4' fluorescent tubes but cdn't succeed. If any one kindly help me by providing a step by step guide with the test voltages etc. at important points in the circuit, I will be ever grateful. The following things have been already done/checked. Physical checking of any defect/damage/burning marks etc., DC voltage after rectification is OK, Filter capacitor (DC voltage  after rectification ) is checked OK, Other electrolytic capacitors chked to be OK, one of the 13005 transistors was found defective - changed with a new one, but no result. Voltages at the transistor terminals seem to be OK.. May pls write to me directly.


Sorry, but my crystal seems to have problems getting me an image of the affected electronics.....