As I understand it when CCFL's age they draw more current. It seems like
some of the inverter problems discussed in this forum might be the result of CCFL's that have aged enough that the current they draw eventually damages the attached inverter. In this situation, one can swap caps and transistors in the inverter to affect a "repair", but since the high current draw remains, the inverter will eventually fail again.
So how to diagnose this situation?
It is easy enough to tell when a CCFL is blown by hooking it to a known good inverter. However, doing that with a high current CCFL will most likely not reveal anything out of the ordinary: the bulb would light "normally" and the test would not last long enough to destroy the inverter. My digital multimeter cannot even measure AC current, and most likely even if it had that setting, wiring it in series with the CCFL would blow up the meter.
Seems like some sort of dedicated circuit is required, one that could plug in between a good inverter and the bulb being tested. Googled for this and found some good/bad type testers like this one:
http://www.lcdparts.net/LST01.aspx
which I don't think would diagnose a low resistance CCFL. Also one analytic CCFL tester, which almost certainly would do the trick, but I couldn't find a price for it, and it looks really expensive:
http://www.nfcorp.co.jp/english/pro/...fications.html
Surely we can come up with a relatively simple/cheap circuit one could place in series with the CCFL which would emit a DC voltage that could be easily measured with a multimeter. For instance, placing in one of the CCFL power leads a small resistor in parallel with a series (diode + capacitor). Set the capacitor value fairly large, and the resistance such that the voltage drop across it is small compared to across the CCFL, but more than 0.7V, and the peak voltage on the resistor should eventually show up as a DC voltage on the capacitor (-.7V), which could be measured with a multimeter. This is simple and cheap, maybe not too accurate, and definitely not very safe, since both sides of that capacitor are swinging up and down by hundreds of volts, so there is plenty of room for blowing oneself up by touching a lead or the test instrument. To be useful we would also need to know what sorts of voltages to expect on good and not so good bulbs.
Anybody have a better idea?
some of the inverter problems discussed in this forum might be the result of CCFL's that have aged enough that the current they draw eventually damages the attached inverter. In this situation, one can swap caps and transistors in the inverter to affect a "repair", but since the high current draw remains, the inverter will eventually fail again.
So how to diagnose this situation?
It is easy enough to tell when a CCFL is blown by hooking it to a known good inverter. However, doing that with a high current CCFL will most likely not reveal anything out of the ordinary: the bulb would light "normally" and the test would not last long enough to destroy the inverter. My digital multimeter cannot even measure AC current, and most likely even if it had that setting, wiring it in series with the CCFL would blow up the meter.
Seems like some sort of dedicated circuit is required, one that could plug in between a good inverter and the bulb being tested. Googled for this and found some good/bad type testers like this one:
http://www.lcdparts.net/LST01.aspx
which I don't think would diagnose a low resistance CCFL. Also one analytic CCFL tester, which almost certainly would do the trick, but I couldn't find a price for it, and it looks really expensive:
http://www.nfcorp.co.jp/english/pro/...fications.html
Surely we can come up with a relatively simple/cheap circuit one could place in series with the CCFL which would emit a DC voltage that could be easily measured with a multimeter. For instance, placing in one of the CCFL power leads a small resistor in parallel with a series (diode + capacitor). Set the capacitor value fairly large, and the resistance such that the voltage drop across it is small compared to across the CCFL, but more than 0.7V, and the peak voltage on the resistor should eventually show up as a DC voltage on the capacitor (-.7V), which could be measured with a multimeter. This is simple and cheap, maybe not too accurate, and definitely not very safe, since both sides of that capacitor are swinging up and down by hundreds of volts, so there is plenty of room for blowing oneself up by touching a lead or the test instrument. To be useful we would also need to know what sorts of voltages to expect on good and not so good bulbs.
Anybody have a better idea?
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