Dell 2407wfp backlight problem

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  • GoNz0
    replied
    Re: Dell 2407wfp backlight problem

    Originally posted by GoNz0
    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...

    Leave a comment:


  • GoNz0
    replied
    Re: Dell 2407wfp backlight problem

    Originally posted by leapius
    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.

    Leave a comment:


  • leapius
    replied
    Re: Dell 2407wfp backlight problem

    Originally posted by sebr
    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?

    Leave a comment:


  • sebr
    replied
    Re: Dell 2407wfp backlight problem

    Any progress lately?

    Leave a comment:


  • budm
    replied
    Re: Dell 2407wfp backlight problem

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

    Leave a comment:


  • leapius
    replied
    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.

    Leave a comment:


  • budm
    replied
    Re: Dell 2407wfp backlight problem

    I will see how much my fluctuates tonight.

    Leave a comment:


  • leapius
    replied
    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.

    Leave a comment:


  • budm
    replied
    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.

    Leave a comment:


  • leapius
    replied
    Re: Dell 2407wfp backlight problem

    ok I rubbered up and found:

    340v - stand by
    465v - powered on

    Leave a comment:


  • budm
    replied
    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.

    Leave a comment:


  • leapius
    replied
    Re: Dell 2407wfp backlight problem

    Originally posted by budm
    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?
    Last edited by leapius; 09-14-2012, 10:19 AM.

    Leave a comment:


  • budm
    replied
    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?

    Leave a comment:


  • leapius
    replied
    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

    Leave a comment:


  • leapius
    replied
    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!

    Leave a comment:


  • jetadm123
    replied
    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.

    Leave a comment:


  • budm
    replied
    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.

    Leave a comment:


  • leapius
    replied
    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?

    Leave a comment:


  • tom66
    replied
    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?

    Leave a comment:


  • leapius
    replied
    Re: Dell 2407wfp backlight problem

    Originally posted by budm
    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.
    Last edited by leapius; 09-12-2012, 10:05 AM.

    Leave a comment:

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