qPCR assays that previously worked perfectly are not working any more and the results are, in a word, baffling (see picture). The amplification appears to work fine until cycle 30 or 35 and then the fluorescence signal crashes. Anyone have any explanation? I'm using an old BioRad iQ5 that worked fine until about a week ago. Is the obvious explanation that there is something wrong with the machine? Or could there be something wrong with the chemistry?
Any help will be appreciated!