FILENAMES:

motorcontroller.jpg

DESCRIPTION:

This is a schematic for the motor speed control from a 
Hardinge HLVH lathe.

Posted by Jim Rozen <jrr0@us.ibm.com>. 

The following description was provided:

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Here is the schematic for the solid state feed module for an
HLVH.  This is the most recent version that replaces both the
original variac and variable resistor, and also the potted
version.   This circuit comes on two circuit boards, one
with the active devices and one with the three power resistors,
and are interconnected with the numbered terminals shown.

At on time some of these boards were stuffed incorrectly so
the 330K ohm resistor was a much lower value and would smoke
on power-up.

I think the MOT C122D1 is a standard SCR, and the NTE6404 is
a device called a "silicon universal switch" which is basically
a diac where the trigger voltage can be set via a third terminal.

Terminals 7 and 8 go to 120 volts (fed from a control transformer)
and the 1 megohm pot is the front panel speed control.