Leroy,
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It would be helpful to get some information to help you.? Is this symptom occurring with the plug-in installed or without?? Do you see the trace when depress the beam finder???
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If you still have the plug-in installed (whether that be an SA or oscilloscope), I would remove it.? Confirm that the 141T is good.? Check your LV and HV voltage rails - make sure they are inspect.? You'll have to confirm all that first anyway before troubleshooting the blanking circuit.
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Let us know what you find.
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-Frank
Frank Mashockie