Studio Beam Fuse problem

I have 2 studio beam pc in show currently. Yesterday, one of them blew out a fuse. It was F1 on the filter board. The fuse looked old and was showing corrosion, so I hoped the fuse was just old and replaced it. The unit came back to life and no problem. Today was tech and so the fixtures were on for about 6 hours when the fixtures died again. I opened it up and the same fuse was blown. What would be causing this? I did notice some blackness at the bottom of the fuse holder. (it looks mildly like corrosion and/or melted plastic... although,I cannot find where the source would be if its plastic).

Any suggestions?
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