Back Light Question

[MrVik]

I have a dumpster Dell E151FPb that recapping recently brought back to life. It has a great looking display, nice and bright. I discovered that the brightness control does not change the brightness of the screen. The OSD looks like it is working but the brightness does not change. The contrast works ok. My question is "Do the backlights control the brightness of the display?" If so, how. If not, the how is the brightness controlled? Thanks, Vik.

[PlainBill]

Re: Back Light Question

I have a dumpster Dell E151FPb that recapping recently brought back to life. It has a great looking display, nice and bright. I discovered that the brightness control does not change the brightness of the screen. The OSD looks like it is working but the brightness does not change. The contrast works ok. My question is "Do the backlights control the brightness of the display?" If so, how. If not, the how is the brightness controlled? Thanks, Vik.

The backlights do control the brightness of the display, although this is often not done well. If the connection to the inverter (or the connection between the inverter / power supply and the logic board) is labeled you should see something like Bri, brightness, etc. The voltage on this line controls width of the inverter's output pulse, and thus the brightness of the CCFLs. A quick test - measure the voltage on the control line as you change the brightness setting. If the voltage doesn't change, the problem is with the logic board. If it does, the problem could be with the inverter or the CCFLs are not properly matched to the inverter.

PlainBill

[MrVik]

Re: Back Light Question

Thanks Bill for the really fast reply. There are two CCFLs and it looks like they are controlled by a LT1451ACN Pulse Width Modulator. Is this what actually controls the CCFLs? I am attempting to hook everything back up and check the voltages on this chip while pressing the brightness button. Nothing I can find is marked bright, brite, etc. so I am flying blind.

I did take apart an old laptop display to see for myself what a back light was. If anyone is interested, I will make and post the pictures later.

[kc8adu]

Re: Back Light Question

there are 2 mosfets that often die when the c5706's short.
the number starts with fu.

[EGuevarae]

Re: Back Light Question

there are 2 mosfets that often die when the c5706's short.
the number starts with fu.

Yep. You can find kits on eBay that have the 4 c5706/07, the 2 FU MOSFETS and a fuse.

[MrVik]

Re: Back Light Question

Thanks for all the great replies! I think we are going to solve this problem.