Hi,
Got a KOGI L4BX monitor with a picture and no backlight. Can I simply use a VOM to test the output from the inverter? Is it typically worth replacing the bulbs? The inverters seem to be about half the cost of the unit so replacement of that part isn't really financially purdent (or is it?).
Thanks for any help!
Kirk S.
No, you cannot simply use a VOM, you need an oscilloscope to check the output. Also be aware that the high frequency and relatively high backlight voltage will require some additional care and safety when measuring.
The inverters are usually very easy to repair for a well experienced technician with lots of smps type of knowledge.
Not really, you'd probably just blow the DMM. You can get CCFL lamps very cheaply and just wire one of them to the inverter for testing, otherwise the inverters can often be repaired or replaced with something cheap and generic.
You wil be suprised by how many CCFL inverters I have repaired by simply replacing the marginal ESR capacitors that caused excessive start up current that blew one of the surface mount fuses.
Very rarely do I see one with any output device damage unless the fuse had been replaced without fixing the capacitor problems first.
Thanks for the information...
I do have a scope however I'm not very experienced using it. Can I simply use the 1000x probe on the output and check for a waveform? It isn't like checking the chopper on the hot side of a SMPS.
Everything is surface mount on the inverter. Do the ceramic caps go bad?
Not all inverters have electrolytic capacitors on them, but most do have some square capacitors that are not unmarked ceramic surface mounts but usually tantalum or electrolytic surface mounts.
Usually the scope probe does not even need connected, just place it near the inverter transformer and if it is running it will be clearly visible by a waveform that is not the usualy 60Hz noise waveform. I use this to confirm flybacks and sometimes horizontal coils to see if something is running or not. It does not tell me if it is running correctly though.
Start by checking the fuses, should be a main power in fuse and probably one on each output transformer and transistor feed. If any of the fuses are open, check for obvious shorted components. If no shorts are found, you can chance replacing the fuse, but there still may be a problem. Without a full schematic or lots of experience, it will be difficult to determine what caused the fuse to blow before replacing it.
If it seems to work with the new fuse, replace the lamps, they might be causing some excessive current draw due to age.
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