This is where to connect the wires on a RD54/Maxtor XT2190. The XT-1140 schematic from Bitsavers is a close match to this drive. U14 pin 13 is the injection point and I used a 10k series resistor. U14 pin 11 is ground. The schematic calls out a LM324 but the part is a LF347. I used limits of 3.5V and 6V around the nominal value of 5V. The MFM reader is not connected in this picture.
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