3M1

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The Tektronix 3M1 (first designated the 067-050, then the 067-0050-00) is a calibration fixture for adjusting the normalizing capacitor behind the plug-in connector in 560-Series scopes.

It consists of a Schmitt trigger that is driven from a single-ended input coming from a BNC connector on the front panel. The Schmitt trigger produces balanced output signals with controlled source impedance. The normalizing capacitor in the scope mainframe is adjusted using a procedure similar to adjusting probe compensation. When adjusted correctly, the voltage division ratio formed by the plug-in's output impedance and the mainframe's input impedance should be a real value which does not change across the specified frequency range of the scope. After the scope is normalized using the 3M1, other plug-ins can be adjusted to produce clean transient response in the normalized scope.

Note that C131 and C136, on the printed circuit board, were set at the factory and should never be touched.

Each of these plugins requires 50 to 100 V square wave pulses to drive the Schmidt trigger, but only the earliest members of the 560-Series scopes have a calibrator output that will go that high. The 3M1 pictured below has been modified to work with 40 V pulses. See the Repair tab for details.

067-050

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  067-500 Front

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  067-500
  Inside Left

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  067-500
  Inside Right

067-0050-00

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  067-0500-00 Front

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  067-0500-00 Schematic

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  067-0500-00 PCB

3M1

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  3M1 Front

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  3M1 Circuit Board
  (note added resistor)

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  3M1 Schematic
  (added resistor on the left)