When a sample and hold circuit fails to hold the sampled value over a period of time. The output of a drooping sample and hold will gradually decrease towards 0V when it is supposed to remain constant. Often this is caused by contamination on the circuit board; dirt, oil, or solder flux residue on the board can create leakage paths between traces that allow the charge on the sample and hold circuit's holding capacitor to slowly dissipate. The other common cause of drooping is a faulty capacitor.