After many hours desoldering my MPguino and prying it apart (I caused some repairable damage in the process) I finally found the reason why my green display was not working as shown in the construction notes when connected to the USB cable. Simply the USB connection does not supply sufficient voltage to power the screen. I checked the input from the computer USB connection with a multimeter, it reads 4.85V. The output from the 5V regulator was dropped further to 4.12V. I had been reading the lecture notes provided by SparkFun electronics website which states that the 5V regulator needs at least 6.5V to give a 5V output. So at this stage my MPguino was in pieces. Soldering it all together required some patience as I had to use individual wires rather than the pin connectors supplied with the kit (those I trashed in my attempts to desolder and pry apart).
Now that the MPguino was together again - this time it was a mess of connection wires (used a few different colours to make it easier to trace the connections) I connected the board to an independent power supply supplying 9V through the telephone cable and plug. Voila! it works as described - seems obvious now - however I had read a post earlier stating that the USB should be all one needs to power the unit up (clearly for uploading the software yes). What I learnt- read the SparkFun electronics website posted lectures explaining what each component does and how to wire a board up and how to load the software - great easy to read notes highly recommended. I would suggest any newbie to electonics like myself reads these lecture notes first. I hope this note helps others.
Thanks to all those that provided tips. Now to install the unit on my 1995 Mercedes E320 (M104 six cylinder engine).
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