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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Need more advice on backlight inverter
Hi again, Some time ago I asked for schematics on my Samsung Syncmaster 531T monitor as the backlight had gone out. I have now pinpointed the fault to one side of the dual inverter. I changed two faulty transistors that drove the output transformer. Then the backlight worked for about 5 minutes, when it started flickering and went off again. The worrying thing this time was that there was a distinct smell of burned electronics around the transformer this time.... Now the transistors are OK, but the backlight goes on for about 1 second, then turns off, probably some protection circuitry switching off. It seems like only the backlight of the part of the inverter that originally was OK lights up. One of my questions now is: Can the CCFL tube fail in a mode that burns the output circuitry. The inverter consists of two identical "channels" of which one seems OK, so I can compare the readings when measuring it, but I cannot really find any differences. I have also tried to connect the CCFL:s to the other tubes channel and then that part turns on for the 1 second period. This seems to indicate that the CCFL i OK ? Any hints on where to start looking. I would buy a new AMBIT inverter, but there seems to be no way of getting them and I am also worried about the possibly faulty CCFL destroying the new one too. -- Dag Nygren email: Oy Espoon NewTech Ab phone: +358 9 8024910 Träsktorpet 3 fax: +358 9 8024916 02360 ESBO Mobile: +358 400 426312 FINLAND |
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Need more advice on backlight inverter
Dag Nygren wrote:
Hi again, Some time ago I asked for schematics on my Samsung Syncmaster 531T monitor as the backlight had gone out. I have now pinpointed the fault to one side of the dual inverter. I changed two faulty transistors that drove the output transformer. Then the backlight worked for about 5 minutes, when it started flickering and went off again. The worrying thing this time was that there was a distinct smell of burned electronics around the transformer this time.... I'm betting on a shorted turn /insulation failure on the transformer secondary. -- http://inquisitor.i.am/ | | Ian Stirling. ---------------------------+-------------------------+-------------------------- Tad Williams has an interesting new fantasy: http://www.shadowmarch.com/ |
#3
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Need more advice on backlight inverter
Dag Nygren wrote in message ...
Ian Stirling wrote: I'm betting on a shorted turn /insulation failure on the transformer secondary. I tried measuring this, and comparing it with the other, but some shorted turns cannot really be detected with a multimeter... Sounds like a reasonable explanation, anyone knows where I can get a CDT239b transformer ? May be possible to use a generic replacement CCFL inverter and rewire the transformer if it has the same primary/feedback layout ? -A |
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Need more advice on backlight inverter
Most likely the transformer is defective. This is common when the
transistors are defective in many of these inverters. You cannot measure this with an ohm meter. Normally these are changed as a complete module when defective. The lamps should be changed along with it, because defective lamps can cause problems as well. Most service departments will change both the lamps and inverter units together, to prevent future problems, and to have peak performance back again. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm ========================================= "Dag Nygren" wrote in message ... Hi again, Some time ago I asked for schematics on my Samsung Syncmaster 531T monitor as the backlight had gone out. I have now pinpointed the fault to one side of the dual inverter. I changed two faulty transistors that drove the output transformer. Then the backlight worked for about 5 minutes, when it started flickering and went off again. The worrying thing this time was that there was a distinct smell of burned electronics around the transformer this time.... Now the transistors are OK, but the backlight goes on for about 1 second, then turns off, probably some protection circuitry switching off. It seems like only the backlight of the part of the inverter that originally was OK lights up. One of my questions now is: Can the CCFL tube fail in a mode that burns the output circuitry. The inverter consists of two identical "channels" of which one seems OK, so I can compare the readings when measuring it, but I cannot really find any differences. I have also tried to connect the CCFL:s to the other tubes channel and then that part turns on for the 1 second period. This seems to indicate that the CCFL i OK ? Any hints on where to start looking. I would buy a new AMBIT inverter, but there seems to be no way of getting them and I am also worried about the possibly faulty CCFL destroying the new one too. -- Dag Nygren email: Oy Espoon NewTech Ab phone: +358 9 8024910 Träsktorpet 3 fax: +358 9 8024916 02360 ESBO Mobile: +358 400 426312 FINLAND |
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