Many of the keys on the Beetel Sigma Basic keypad had stopped working. I had some free time and I figured I might as well open it up, give it a clean up job and see if that makes any difference. I found loads of dust on the membrane below the keys and it was a bloody pain putting all them back into the slots. The circuit behind the membrane was glued to the red 'in-use' LED. When everything was put back the way it used to be I was pleasantly surprised to find the 'supposedly dead' keys working again!