When I try to switch on the phone I get a white screen(back-light on). To switch it off I need to take out the battery. I've found some repair guides saying 'apply this jumper' but I don't know exactly what it is.

I know it's an old phone but I'm just trying to repair it.
Thanks in advance

It's not worth the trouble to fix. FWIW, I am a senior Nokia systems engineer. You can get a Lumia 900 for about $50 USD these days. I'm using one for my primary phone, and it isn't bad (very good, actually). I also have a Google Nexus One running Gingerbread, a Nokia N8 running Symbian, and a Nokia C3-00 feature phone. The 900 is the best of the lot. I used the Nexus One almost exclusively for 2 years and thought it would be hard to find a better phone, but the Lumia 900 has a lot going for it, including the ability to handle my personal gmail account and contacts lists seamlessly. That was important to me as I have a lot of gmail contact lists for things like the IEEE consulting group that I am an officer (past president) of.

If you want to wait a couple of months, you can get the new Lumia 920 with inductive charging and multi-tasking Windows 8. Unfortunately, the company probably won't be giving me one until sometime next year! :-)

Now Nokia is looking good

May be because of battery problem or you are trying to switch it on when it is in charging mode.

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