"non-polar" capacitor?

Since I acquired a Coco Orchestra 90 unit awhile back, and I am trying to find the source of some humming in my system when the Orch 90 unit is operational, I looked at the schematic: http://www.colorcomputerarchive.com/coco/Documents/Manuals/Hardware/Orchest… (page 109 of the PDF) I understand the ROM, the resistor ladders, and the latches, but analog is not my strong suit. I made my way through the op-amp design, but I am stumped on one component (actually three)? C7,C9, and C10 They look like electrolytic polarized caps, but are NP (non polarized), with no '+' on the schematic. Can someone shed light on what these are and where you would find them (or if they can safely be replaced with another kind of capacitor)? I will admit I've never seen mention of these before now. Are they "bipolar"? http://www.digikey.com/product-detail/en/nichicon/UVP1H010MDD/UVP1H010MDD-N… Or, are they called something else now? Jim -- Jim Brain brain at jbrain.com www.jbrain.com