Users have identified the problem as faulty sensors however the problem is not faulty sensors but rather faulty filters. It appears that poor quality control has resulted in residue in the filters which causes them to become opaque. The solution is not too difficult but is a little tricky. The fix requires disassembling the device and cleaning the crud off the filters. This is a slightly hazardous operation and could potentially break the device if not done carefully but without it the device is useless so what have we got to lose!

To disassemble the device requires placing a small flat headed screwdriver into the hole just above the USB cable entry. Lifting the screwdriver carefully separates the top and bottom. Be careful as it is easy to break the clips. However the device can be held together with tape or glue after the fix if the worst comes to the worst. Next set the top aside and remove the clear plastic fascia. Next gently pry the board from the base. Note that the clips break easily and that the board may have adhered to the base near the top end (the sensor end). Now check there is no glue over the 3 sensor pin-holes in the black tape on the underside of the board. Then set the board aside.

The fix involves removing the 3 filters from the base one by one and cleaning all the parts and reassembling. To clean the parts I used a toothbrush, some tissue paper and wax polish. (Don't use an alcohol based solvent or you may destroy the filters!). The filters consist of five parts. The black 'O' shaped retaining sticker, a small square block of coloured perspex, and 3 square pieces of coloured perspex filter paper. These pieces are small (approx 3-4mm square) and easily lost so take care not to sneeze!

Start by removing the top black 'O' sticker. Use a pin or needle to lift the sticker then pry off with a pair of needle nosed tweezers. Set to one side. Carefully remove the perspex block and the 3 filters. The filters may be stuck together and to the bottom of the block. Carefully ply them apart and set aside. Clean each filter component by holding with the tweezers and carefully brushing with a clean toothbrush. Finally spray some wax polish on the tissue and rub the piece until it is clean and dry. Repeat for each element. Clean the hole in the base and reassemble the filter by placing the odd coloured filter in first and then the two same coloured filter pieces and finally the block. Then cover with the black sticker with the hole central to the base. Clean off any excess glue.

Now repeat the procedure for the other two filters. After completion you should be able to see through the each filter as if you were looking through coloured glass. Now the light will be able to get to the sensor and the device should work. Reassemble the device by placing the board back on the base. Note that the sensor pin-holes on the board should line up with the holes in the filter stickers on the base. Next place the fascia on the board. At this point (before full reassembly) you may wish to test the device. Place the top on the device but do not push in the clips and hold in place with tape or blu-tack. Run a test and see the calibration results. If all is ok carefully push the top on the device and you are finished. If not you may need to check your cleaning and repeat the cleaning procedure.