Ok, I'll come clean. My latest project is to try and get my car charger which worked with my old Nokia to work with my new one. It seems that the newer Nokias are very fussy about what you plug into the power socket. Also I can't find the specs for what voltage/amperage it needs.
I have done a little research on usenet and found details of someone who had succesfully modified one of these units, but he was dealing with 2 units one of which worked and had a mod and one which didn't he applied the mod (extra resistor) and all was well.
This unit is based around a MC34063A DC-DC converter.
I have put the thing on the bench and found it is putting out a little over 5V and is certainly capable of supplying 500mA.
I have just put a genuine Nokia mains charger (which I know will charge the phone) on the bench and checked it's output. It was marked as 3+ volts at approx 300mA it actualy gave 4.5V at 300mA.
On this face of it, this doesn't seem that different.
Does anyone know what these modern Nokias actualy need?
Could it be that it doesn't like getting more than 4.5V?
Have just read the back of another mains charger (the one which came with this phone and it says it puts out 8.5V at 800mA).