I take it your monitor's power cord and video cable do not come with built in RFI filters? They do sell RFI filters and, if your video cable doesn't have one, there are ones you can buy with them built in. For the power cord, there are several ways to RFI proof it. There are large RFI toroids you could wrap the ac cord around and there are some RFI iso-transformers. First you need to determine if the RFI is being radiated from either or both cables or from the monitor itself.
AM is open to just too much interference. Maybe see if you can place the AM radio on a separate power circuit and it cuts the interference. If so, it's coming through the power lines. If not, try orientating the AM radio and its internal antenna to see if RFI increase/decreases with certain orientations. If it does, then it is being radiated by either the cables or directly from the monitor itself.
Not sure it would be worth the effort of trying a different horizontal scan rate. Maybe a large sheet of aluminum may help you pinpoint the source if it is used as a shield. Once the actual source is found, you'll know if you need to buy a RFI filter or new video cable with filter or not. Of course, if the RFI is being radiated directly from the monitor itself, it will be hard to filter.
Edited by Major Payne, 07 July 2008 - 02:25 AM.