i was confused about ChIP result - i need help (May/17/2008 )

sorry for no pic

i use two pairs of primer to run pcr after DNA extraction, the positive primer 's product was good ,that is Ab got band ,wAB no band ,and input got band . but the result for the other primer was not satisfying, cause ab and input got bands,but wab got band too(thinner), why ?
i used the same template
i'm studying the transcription factor-promoter reaction? is it possible that the same TF binds differently for different promoter?

what is the most possible reason?

any help would be appreciated

First, there is some nonspecific pulldown of DNA in your sample that can only be amplified by your 2nd pair of primers becuase it is more efficient than the first pair.