Shows the working led lamps working. There are 200 LED's in parallel with a power supply rated at 3.5V 1.5W, which was confirmed as approximately correct (3.4V off-load).

In the non working state, the on-load voltage was 1.8v, and using 1W, explaining why the LED's were not illuminating (They need a threshold of about 3v). This suggested there was a slight short somewhere, but nothing was obvious.

The short was easily found in a string of 200 LED's with a thermal imaging camera. (You don't need one, it just explains how I found the location of fault )