@jeff: You mean that the wire to the lamp is bad or lamp is worn out with blackened ends?
It has a bad CCFL lamp, that will not light at all. The inverter goes into shut down once it knows it will not come on (over voltage on transformer secondary).
I did find parts relativity cheap. But I've always wanted to do my own DIY LED conversion. So I think I'm going to use this as an opportunity to do just that.
I have this exact same monitor with the same inverter that just went bad.
It started making a whining noise one day and the screen got very dim, then went out completely. When powering up now, I get the squeal from the inverter for a few seconds, then it shuts down.
It's been a good monitor and I hate to trash it, so I'm having a look to see if there is any practical fix. I've taken it apart and have the inverter board accessible. The oscilloscope shows approx 24V DC and a flyback waveform (momentarily) on the primary of the CFL transformer. The high side secondaries are covered in glue and I haven't tried to probe them yet. The text on the topside of the board says those outputs are about 1KV.
I don't have spare CFL tubes to swap out. Is there any way to measure the signal at the bottom end of the CFL tube (across the sense resistor) and determine if the problem is the tube or the inverter?
I have gathered that I can't just unplug 3 of the 4 tubes and test them individually since there is an open-tube protection circuit.
See budms signature files above - you can make a test bulb from a cfl.
First test is usually the secondary resistance on the inverter transformer?
If they are ok then it is on to bulbs and wiring.
I did some investigating with the oscilloscope, and found that the power supply to the inverter (around 24-28 VDC) looked really bad when the inverter tried to start up:
(Note - probe type is not recognized by scope - multiply voltages by 10)
There shouldn't be that type of waveform on a power supply, so after considering the name of this forum, I inspected the capacitors (these were 220uF 35V - effectively in parallel because the inductor shown on the silkscreen was replaced with a jumper). They were a bit swollen, so I replaced them.
The originals were CapXon - I replaced them with Nichicon.
After that the DC going into the inverter was clean and the whining noise was gone, but the backlight still doesn't work.
Probing on the high side of the drive transistor going to the inverter transformer (collector? drain? ... don't know - I have not been able to find a schematic for the Darfon supply), I see a waveform run for a couple seconds and stop. This repeats 3 times, then stops and a yellow LED comes on in the switch panel.
Waveform at inverter drive (20uS/Div)
Waveform at inverter drive (50mS/Div)
So there is still something wrong that is shutting down the inverter after 3 tries starting up.
The inverter IC/Transistor (5 pin DPAK on back of board) is labeled:
NIKOS P2804ND56
U145J009B
The other IC in the inverter area (SOP package) is labeled B113715 FC27G P0810
Check the high voltage windings of the inverter transformers as suggested, DARFON is known for having bad inverter transformers, I replaced many of them.
After looking at previous posts, the inverter IC is BIT3715, and the FET driver is P2804ND5G. The text on the parts was somewhat unreadable on my board, but based on previous posts, I'm pretty sure they are the same.
Next step is to test the transformer windings, but I'll have to get back to it in a few days.
You should make a couple of test lamps to help you narrow down the problem so you will not waste lots of time trying to fix the board if the board is not bad like this example here: https://www.badcaps.net/forum/showth...t=33720&page=3
buenas tardes mi nombre es marcos soy de venezuela... y estoy en este foro para ver si me pueden ayudar con un problema q tengo con mi monitor especificamente la fuente de poder modelo DARFON B092-XXX Quiere camiarlos con condensadorles y los retire para los estravie y quiera saber quien me puede ayudar con decir los voltales y uf q cada uno de ellos se los agradeceria....
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