Dell E196FPf all white after recap

[0r3n]

Hi,

i have a Dell E196FPf monitor that showed a very "low light" picture.
i mean that i had to turn off all the lights in my room to hardly see what's on the screen.
so i opened it and saw 2 220uF 25V bad cap's, i replaced them with 2 330uF 25V caps (this is what i had and i understood that i can replace the 220uF caps with up to 440uF caps with same Voltage).
after that, i turned it on and all the screen is white, the light is ok, but white screen is all what i got.

what should i check more?

here's some pictures of the board:











thank you,
Oren.

[Rtech]

Re: Dell E196FPf all white after recap

Again,ensure that the cable from the Board to the LCD Screen is in correctly.Also use the 'manage attachments' facility for the photos.ALSO as this is hapening on 2 of your Screens, suggest you look at the input cable fom the PC and if necessary the Graphics card.

[PCBONEZ]

Re: Dell E196FPf all white after recap

Changing uF that far is not a good idea.
And you need low ESR caps. - Not the junk Radioshack caps.
.

[0r3n]

Re: Dell E196FPf all white after recap

uploaded the pictures to this post.

Rtech,
i just checked the D-Sub cable again, and working fine on a good monitor.

PCBONEZ,
i understood that i can put up to double of the original caps, so i took those caps from an old MoBo, thought they will be fine. should i order new caps from ebay? i read here that it's not that good to recap a lot of times... afraid to damage the PCB...

[Rtech]

Re: Dell E196FPf all white after recap

Assuming the caps you changed were C1 and C9, these would not effect the video out, as those are part of the Inverter/Backlight circuit.
Your first port of call is to measure the voltages on U801 and U802,which are located just to the right of the Large Cap.Put the negative probe of your meter(I assume you have one !!) into the VGA Screw hole, and then measure the DC Voltage on each of the pins of the 2 voltage regulators, and advise the readings you get.

[alexanna]

Re: Dell E196FPf all white after recap

i just checked the D-Sub cable again, and working fine on a good monitor.

The D- sub cable is not the correct cable,you need to check the flat cable from the logic board to the LCD panel

[PlainBill]

Re: Dell E196FPf all white after recap

uploaded the pictures to this post.

Rtech,
i just checked the D-Sub cable again, and working fine on a good monitor.

PCBONEZ,
i understood that i can put up to double of the original caps, so i took those caps from an old MoBo, thought they will be fine. should i order new caps from ebay? i read here that it's not that good to recap a lot of times... afraid to damage the PCB...

I'm not sure who told you that, but as a general rule, changes in capacitor value should be made only if you understand the function of the capacitor. Many capacitors perform some timing function. Change them and the circuit may not work. Sometimes filter caps are selected to establish power rise times. Again, a significant change in value can upset that.

If memory serves, a year or more ago someone substituted a higher value cap in the power supply of his signal card and discovered it wouldn't work at the higher resolutions. Installing the proper value corrected that.

As to the specific problem you are now seeing, the most common cause of 'white screen' is an improperly seated ribbon cable from the signal card to the LCD panel, just like alexanna suggested.

PlainBill

[Rtech]

Re: Dell E196FPf all white after recap

Post #2 was his reason for checking the cable, as it was a simple thing to do,and you never know,and was asked to do the logic to LCD one as well,as yet he has not confirmed that he did so.

[retiredcaps]

Re: Dell E196FPf all white after recap

i understood that i can put up to double of the original caps, so i took those caps from an old MoBo, thought they will be fine.

Re-using old caps without testing them for capacitance and ESR and making sure they are within spec is not recommended. It is like taking a 9V battery out of 5 year old toy and putting it in a smoke detector and living with a smoker who smokes in bed.

Caps are relatively inexpensive and new ones should be purchased from reputable sources like digikey, mouser, badcaps.net store.

[PCBONEZ]

Re: Dell E196FPf all white after recap

If you are in the US then buy from Digikey, Mouser, Bdent, or Badcaps.net.
If outside the US try RS.

There are WAY too many fakes on ebay. [Crap brands remarked as good brands.]
If you really REALLY know what you are looking at you can do okay on ebay sometimes but even then once in a while you'll get burned.
.

[PCBONEZ]

Re: Dell E196FPf all white after recap

There is another problem with reusing electrolytics.

The voltage rating is based mostly on the thickness of the dielectric.

In Aluminum Electrolytic caps the dielectric is an oxide layer on the aluminum that is chemically active with the electrolyte.
It changes thickness [and hence, effectively, the voltage rating] based on the applied voltage.
If you take a 35v cap and use it on a 12v circuit after about an hour it is really only a 12v cap despite what it says on the sleeve markings.
If you then stick that cap on 25v [or something more than 12v] there's a fair chance it will short internally due to excessive leakage currents through the dielectric.
.
I've seen 16v and 25v caps on motherboards that were actually on 1.5v.
.