Troubleshooting PCR contamination - (May/01/2006 )
Hi there
Negative bands!!!!!!!!!Arggggghhh!!!! I share the same problem with you. I was delayed at least 2 months worj due to contamination. I changed everything including the PCR chamber. But i still got the negative band. But nowadays im getting a clean gel. Im not sure what was the reason but no problem yet. But im so sure it will be back after few weeks or months.
I doubt my primers, im using 16S rDNA universal primers mayb the cross contamination was picked u by my primers. Im not sure. I really hope you problem will disolve away as its really o frustrating to get this negative band. 
Not worth the hassle of diagnosing false positives. I always make 100uL aliquots of buffer, NTPs, primers from a clean stock tube. When things start going wrong, just chuck em out and start again.
Pipetting will always aerosolize DNA - pipette barrels seem to be filled with the stuff.
my gell os temporarily clean now, our lab is using diluted bleech to wipe down the benches and clean other things. But we'll probably die before the DNA contamination. 
Negative bands!!!!!!!!!Arggggghhh!!!! I share the same problem with you. I was delayed at least 2 months worj due to contamination. I changed everything including the PCR chamber. But i still got the negative band. But nowadays im getting a clean gel. Im not sure what was the reason but no problem yet. But im so sure it will be back after few weeks or months.
I doubt my primers, im using 16S rDNA universal primers mayb the cross contamination was picked u by my primers. Im not sure. I really hope you problem will disolve away as its really o frustrating to get this negative band.
Try preparing your samples in a hood.