I have a mk.1 Nexus 7 that is now stuck on full brightness
I can go into settings and adjust the slider and flick it on and off auto brightness but that makes no difference

I cracked the screen a while back and a colleague replaced that for me, however I also updated the OS to 4.4 at the same time he fixed it so i’ve no idea if my problem stems from a software or hardware fault

any ideas folks?

it may be the light sensor that’s broken. You can download an app to test how it’s working.

I fixed mine on my phone by using a vacuum cleaner to remove some dust that had got stuck covering the sensor.

Just read this which may help you:

Fix auto-brightness problems – Android 4.2 has an auto-brightness setting, but it doesn’t work very well. You should download Lux Auto Brightness to fix this problem. Lux automatically adjusts the brightness of your display based on your environment. When you go into a dark room, Lux will automatically lower the brightness of your display after you unlock your screen to make reading more enjoyable.
To setup Lux you need to go through their setup wizard. I suggest you leave the factory default settings as is. After you do that, you’ll need to go back and launch the app again and touch ‘Press to enable Lux.’ Lux will adjust every time you unlock your screen. Although there is a dynamic setting, it doesn’t work as well, because it’s possible for your finger to occasionally block the light sensor when you hold the tablet in Portrait mode. If you sometimes use your tablet in a totally dark room, I suggest you go to the settings page and set ‘Night Mode’ alpha to 10.

From http://mostly-tech.com/2012/11/28/more-great-tips-tricks-for-the-nexus-10-and-other-android-devices/

Ok i’ve run one of the diagnostic apps and it’s showing that the brightness sensor is working fine (within the same sort of scale of my galaxy s4 running the same app)

looks like it’s a software issue so i’m going to force a reinstall of the android operating system as a factory reset did nowt