Resolved Screen Problem after Replacing HD

[Colonel Panik]

Hi,
I've replaced HDs in iMacs before, but this time I've done something wrong and the screen now looks washed-out. All the colours display properly, its just like it's over-exposed. I can change brightness and the screen gets dimmer or brighter, but it has no effect on the washed-out appearance.

I've checked that the display power cable is seated properly. I can't see this being an issue with the screen's thermal sensors, which weren't detached.
If it was a backlight problem, I'm sure that the screen would get very hot, and this isn't happening.
I'm 100% sure it's not a software issue. I've checked Sys Prefs > Display contrast and everything is as it should be.

iMac Early 2009 24"
As you can see from the photo, some shades of grey are appearing as red pixels.
Any ideas?

 

[_Kiki_]

Which model of iMac?

 

[Colonel Panik]

Sorry, forgot to add that. I've updated the original post. Thanks.

 

[DeltaMac]

Did you try reseating both ends of the LVDS cable and the inverter cables? The LVDS is the larger, ribbon cable, held in place by 2 screws to the logic board. The OTHER end of that cable (attached to the back of the display) can get disturbed during repairs, even though it would not usually be touched during that process. If that careful reseating does not help, then most likely you need a replacement LVDS cable.
You may also try an external display, connected to the mini DisplayPort, to see if you have a general video card problem where you have a similar appearance on the external display.
If the external shows the same problem, then video card, then logic board.
Hopefully, a cable reseat will fix...

 

[Colonel Panik]

Did you try reseating both ends of the LVDS cable and the inverter cables? The LVDS is the larger, ribbon cable, held in place by 2 screws to the logic board. The OTHER end of that cable (attached to the back of the display) can get disturbed during repairs, even though it would not usually be touched during that process. If that careful reseating does not help, then most likely you need a replacement LVDS cable.
You may also try an external display, connected to the mini DisplayPort, to see if you have a general video card problem where you have a similar appearance on the external display.
If the external shows the same problem, then video card, then logic board.
Hopefully, a cable reseat will fix...

I reseated the 2-screw LVDS cable a number of times, it's possible I disturbed it by pushing it in too hard. I poked at the other end of the cable, but it's so wrapped in tape that I can't see how it would get unseated.
I'll get an external display and see if that works. If it works fine I'll rip the tape and have a look at the other end of the LVDS cable.
I can understand the backlight getting disturbed, but I haven't found any pale/low-contrast screen issues on google...
[doublepost=1502994543][/doublepost]So I hooked up an external monitor and the image on that is fine... so I guess the LVDS cable is the main suspect...
(I didn't think the iMac would drive the external monitor as it's huge, but it worked a treat.)

I'll check the cable in the morning.
Cheers.

 

[Colonel Panik]

Update.
I tried reseating cables many times, checked for other loose cables... Nothing.
Then I decided to reset the PRAM and... perfect monitor once more.
Crazy.