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Hi Arnold,



Hope this gets to you.



This is not the schematic, however it is the service manual [very slim
version].

From the picture, you have ONLY one 50 ohm resistor in series with the
INPUT; that looks like an SMT resistor with a very low pulse power spec., or
low voltage rating.

If the scope was used with probe and AC INPUT, only high voltage or pulse
power would have opened the resistor, not DC voltage.

Do you know what type of equipment your friend was troubleshooting?

I have only used crowbar circuits on High Energy circuits, so that the
voltage, current, or energy is disabled BEFORE any damage can happen to
components or circuitry.



//John KC1GJE