IBM 3270 Maintenance Manual page 226

Check for an increase in voltage (approximately
0.2 V dc) at the respective points below:
• For a Type 1 diskette drive, check point TP-5
of the diskette-drive logic board while the
LED is on during POST.
• For a Type 2 diskette drive, check point U6-!
of the diskette-drive logic board while the
LED is on during POST.
Type 1
Type 2
DOES THE VOLTAGE INCREASE WHEN
THE LED IS ON?
NO
Replace the diskette drive (see Section 5,
"Removal/Replacement and Adjustments").
YES Go to page 3-600-34.
October 1984 3-600-27