I know it's tough sometimes when you're trying to get the rig up and running, but try to be methodical when doing troubleshooting on this transmitter. What I mean is to check voltages, currents, forward and reflected power from one end to the other. Start with exciter drive, making sure you have drive going to your IPA, then that your IPA isn't folded back with reflected power from the grid. If the IPA does have excessive reflected power or lack of drive then look to your tube, socket assembly, externally mounted caps, ect.
Generally a screen cap that blows through the Capton is caused by excessive screen voltage, a tube with a screen to plate short, really bad tuning, or dirt. The challenge is that once it arcs through the capton film, a carbon trail has been created in the copper. Just replacing the capton usually won't work because chances are good it will arc right at the carbon points. Unless you can completely eliminate the burned spots, this problem will keep happening, even at lower voltages.
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