Dell 2407wfp backlight problem

[GoNz0]

Re: Dell 2407wfp backlight problem

super necro post but could you guide me to the offenders please?
I have a working one to try and figure out what parts I need so I may be able to take a reading from them when I know ones they are.
Thanks.

I got this out again today and can't for the life of me figure out what parts bad

Did the 3 caps and the suspect on the power board last year get the same results as the OP...

[GoNz0]

Re: Dell 2407wfp backlight problem

Well, yes actually. I worked out it was the cermic capacitors on the other side of the transformers on the inverter that were at fault. Unable to replace these due to lack of equipment to identify the capacitor types and resolder such small components I ordered a new inverter from aliexpress, which worked fine. The bulbs light up fully.

The one problem that remains is that after a while the bulbs will go fully bright and are not affected by reducing the the brightness using the controls. This might point to why the original inverter broke down in the first place?

super necro post but could you guide me to the offenders please?
I have a working one to try and figure out what parts I need so I may be able to take a reading from them when I know ones they are.
Thanks.

[leapius]

Re: Dell 2407wfp backlight problem

Any progress lately?

Well, yes actually. I worked out it was the cermic capacitors on the other side of the transformers on the inverter that were at fault. Unable to replace these due to lack of equipment to identify the capacitor types and resolder such small components I ordered a new inverter from aliexpress, which worked fine. The bulbs light up fully.

The one problem that remains is that after a while the bulbs will go fully bright and are not affected by reducing the the brightness using the controls. This might point to why the original inverter broke down in the first place?

[sebr]

Re: Dell 2407wfp backlight problem

Any progress lately?

[budm]

Re: Dell 2407wfp backlight problem

Your conclusion is right, some how the inverter just cannot handle all the lamps.

[leapius]

Re: Dell 2407wfp backlight problem

Thanks budm, so a recap:

- solid voltages to inverter board.
- inverter capacitors changed.
- with 3 of the 6 bulbs connected they will come on fully bright (for 2 secs obviously).
- the more bulbs I add in the worse the problem gets.

It seems like when there is more load on the inverter board it just can't strike the bulbs fully and they are dim on the far side. Any ideas what can cause a CCFL bulb to only half light in this situation?

Thanks.

[budm]

Re: Dell 2407wfp backlight problem

I will see how much my fluctuates tonight.

[leapius]

Re: Dell 2407wfp backlight problem

Sorry my bad I just check again:

~ 335v - stand by
~ 370v - powered on

They seem to fluctuate maybe +-5v with my tester.

[budm]

Re: Dell 2407wfp backlight problem

465V! That is way too high, the cap is rated at 450V (in my 2407). Are you sure? The symptom you are having is very strange is that the 19V power supply is OK, the voltage is correct.

[leapius]

Re: Dell 2407wfp backlight problem

ok I rubbered up and found:

340v - stand by
465v - powered on

[budm]

Re: Dell 2407wfp backlight problem

Yes, Red probe on the positive leg, black probe on the neagtive leg, be real careful because you will be working on the Hot (LINE) side of the circuits.

[leapius]

Re: Dell 2407wfp backlight problem

Can you monitor the DC voltage on that 450V cap when the monitor is off and when the monitor is on?

Can you tell me how to do that? red wire onto positive side and black wire to negative side and turn it on with multimeter set to volts?

[budm]

Re: Dell 2407wfp backlight problem

Can you monitor the DC voltage on that 450V cap when the monitor is off and when the monitor is on?

[leapius]

Re: Dell 2407wfp backlight problem

Well I have now installed all new nichicon capacitors on the inverter and sadly there is no change in the backlight. It exhibits the exact same symptoms as before. Any ideas anyone? Would it be worth trying to source a whole new inverter board?

Thanks

[leapius]

Re: Dell 2407wfp backlight problem

Right, I'm going to order some new capacitors and replace them. Thanks for the advice guys. I will report back my findings when I've changed them!

[jetadm123]

Re: Dell 2407wfp backlight problem

Agree with budm that you should replace the 3 caps on the inverter board, as TDK had a bad habit of using poor quality caps in their inverter boards.


Also, if you have the same power supply I mentioned a few posts above, then you might also consider replacing the large 450V cap as it has given other members problems.

[budm]

Re: Dell 2407wfp backlight problem

They are not driven fully, I would try those three caps on the inverter board first. I have seen this symptom on inverter board with bad transformer and bad caps but since ALL the lamps are acting the same then not likely to be the transformers. Those 3 caps are connected in parallel.

[leapius]

Re: Dell 2407wfp backlight problem

The picture is fine - obviously just dimmer on one side as can be seen in the photographs. I'm not sure whether it suddenly went like that or if it was a gradual deteoration - it was just presented to me like that.

What could possibly cause the CCFLs not to light up fully in this way?

[tom66]

Re: Dell 2407wfp backlight problem

So, otherwise, the picture is good, but obviously going to be dim on one side? Did it get worse progressively or suddenly?

[leapius]

Re: Dell 2407wfp backlight problem

Do the lamps stay on like that or they shutdown after a few seconds?

The lights all stay on like that permanently (just dim and flickering on the far side). If I unplug 3 of the 6 bulbs the remaining 3 will come on fully bright (but only for 2 seconds because of the feedback loop obviously). The more bulbs I add back in the progressively worse the problem gets. It doesn't matter which bulbs I unplug just the number. They will all stay on if I plug at least 4 bulbs in.