2-There is a capacitor connected to the filament, in many cases the capacitor was short CCT this was the only fault. Replace the capacitor removed fault Voila, CFL is back to life.
3-CFLs with blown fuse, It was mainly caused by a fault in DC bridge cct., I simply replaced all the rectifying diodes (I have tons of them in my lab) and voila, rebirth of another CFL.
4-Another common fault in the CFLs was Short 400V capacitor that I assume had caused damaged to the transistors and resistors connected to them. There was no sign of resistor color codes as they were to dark ( I assume caused by overheat) but I had plenty of similar CFLs in hand and I checked the one with good resistors, Their value of the first resistor was around 2 ohms and the other around 20 ohms. I also had to change the transistors as well. Another CFL brought back to life.
5-Diac and its 500Kohm resistor at fault .In a few cases, I found the 500Kohm resistor to be open cct. ,And in some cases changing the diac itself resolved the fault.
Hi Mayer,Below is my experience.Not sure if it helps.
HI oldturkey03,In case this can help anyone.Just a modest simple effort to save our Planet.
'''Caution, There is a 400V capacitor in the cct, THIS NEEDS TO BE DISCHARGED PRIOR TO YOUR WORK,I DISCHARGE IT BY CONNECTING THE SOLDERIN IRON’S POWER PLUG ACCROSS IT. Make sure you take the measures to discharge it too.
Here is a summary of what I experienced so far, just to remind you that I had tons of faulty CFLs and that helped me a lot to exchange parts to find the faulty one. It would have been impossible to succeed without so many in hand.
1-One thing I learnt was that to check the bulb filament first because this part is not repairable and I could not found a replacement part in the local market. This will save your time and efforts greatly.