Presario C500 display problem

Hi There, I just got a Presario C500 with broken left hinge and display prob. Display is grey with thin red pink, sometimes green and thick white lines top to bottom (one of each). Top third of screen has changing white horizontal lines. Replaced hinge and screen cable, still the same, looked at plug pins with a magnifying glass, all pins OK. Works fine on external screeen, I guess it's LCD or GPU. How can I be sure?

Yes and no. The Compaq LCD does seem to be faulty. But when I substitute a known working screen it shows pink with many white lines down it. I reckon the GPU is faulty (i.e needs reballing) as is a known fault on Compaqs, what I thought was a faulty ribbon cable was probably the GPU being tweaked when the screen hinges moved. Incidentally when the Compaq screen is put in another laptop I get the same 3 or 4 coloured lines as before with various backgrounds but no detail image. I've had laptops before that power to external screen but won't display on the lid screen, maybe it's not the GPU itself, strictly speaking but it sure can be the connections on it.

I am sure of the replacement screen, it works 100% on a Fuji and it's a listed replacement (LG Philips) LP 154W01 (TL) (D2), which as far as I can see is the LP 154W01 (TL) (D1) from the Compaq but without the brackets. I have already changed the ribbon cable. I have brightness to the screen and therefore the inverter works, image data is nothing to do with the inverter. I'm 90% sure there is discontinuity betweem the GPU internal circuits and the motherboard lid screen output plug. Just to recap, Good (Fuji) screen shows brightness and colours but no details e.g. bios/ Windows text on the Compaq. Faulty Compaq screen shows 3 or 4 coloured lines T to B and (sometimes) flickering white lines at the top of the screen on the Compag and the same T to B lines on the Fuji but no text or flickering. The symptoms do alter from time to time on the Compaq. I might try another (Compaq) ribbon cable but it's unlikely I have 2 bad ones. Moving the cable about and pinching it (on the Compaq) does nothing but (sometimes) moving the screen on it's hinges or flexing the hinge mounting does make a flicker. I can't be certain that the motherboard doesn't have a crack or break since the laptop may have been dropped (L/H hinge was broken). Thanks for your help!

I didn't try another ribbon cable as the supplier 100% guaranteed the one I bought. I did however check all connections from the 30pin LCD connector to the MB connector with a meter at the same time flexing the cable (I had 4 hands, wife helped me)- was unable to find any fault with the cable continuity. I then removed MB and checked all visible solder joints, the ones on the MB output looked grey so I resoldered them nice and shiny. Still no improvement, will have to try a 'new' MB. By the way the onboard display has stopped showing any horizontal lines now but the inverter is still altering the brightness up and down according to image (as displayed on the external monitor) and the 3 or 4 coloured vertical lines still come on when an image should be showing. I WILL SOLVE THIS!!!!

The problem is resolved!!! I put in another motherboard and the fault cleared. I reckon the solder joints under the GPU were not good. Since it'll cost me £60 to find out for sure (GPU reball) I didn't go there. I guess I could have heat gunned the GPU, but better not to, I think! The onboard LCD was faulty also, as I think I said in a previous post (won't show an image). Thanks to all of you who put your brainpower into helping me. Two things come out of this:

1. There can be 2 faults (or more) at the same time in the same area

2. Just because the external screen works, doesn't mean the GPU is outputting to the onboard screen.