The Scooter is from Taiwan, not particularly common but a dig on the web bought some useful information.
Workshop manual here :
Parts list here
And a nice snippet about speedo calibration lifted from a forum:
"Switch to TDO on the LCD and hold down on the right Handlebar button. Change the 4-digit number to 1840"
Adjusting this number adjusts the cal....
I was hoping to find that this had reset to zero but alas that was not the case, readign was set to 1840.
The electrical diagram showed the speed sensor was two wires into the main brain.
A quick look on the bike showed speed signal is derived from the front wheel, there is a magnet mounted on the front disk. This passes a sensor. Spinning the wheel gave no reading. Rapidly moving a magnet past the sensor briefly on one occasion gave a speedo reading ! This tended to indicate a faulty sensor.
The parts diagram showed you could unplug it before the brain. I had assumed this would be a magnetic reed switch so split the connector here and measure ohms of the reed.
I thought I would check the dash by rapidly shorting the cable leading to the brain (to simulate a good sensor being made and broken by the magnet). This gave no reading still and showed something didnt add up. I decided to measure at the brain to check the signal was getting there. Removed the speedo cowling, lifted the clocks (this is what Im calling the brain) went to check the cable leading to it and it just pulled away from the clocks !
I didnt take a pic but the connector to the clocks is the same as a motherboard ATX power connector.If you have ever fitted / removed one of those you will know it has a very strong latching mechanism and shouldnt just fall off !
So success, a loose connector the the brain all along, but interesting to trace it from the wrong end !
Now, rapidly shorting out the lead to the brain with a piece of wire registers a speed reading on the dash.
.. however, removing the sensor we managed to damage it. Should be simple enough to repair without getting a new original part (hard to see but the reed is embedded in some kind of resin and is cracked).
The bike doesnt seem so well supported (not sure if it still imported to the UK) but as per other comments I was finding on the web it looks good, is nicely made, components largely seem of good quality.
here is the new reed fitted. I sealed it back in the housing with silicon sealant.