Specifications

Page 12 Installation Instructions: SCSI Disk Drives
Checking Individual Peripherals for Shorts to Chassis Ground
1.To determine if a peripheral is shorted to chassis ground, disconnect the
peripheral’s power and interface cables, but do not loosen or remove any
of the peripheral’s mounting hardware. Use an ohm meter to measure
between chassis ground and either of the two middle pins on the
peripheral’s power connector. The power connector has four pins; the two
outside pins are power; the two inside pins are ground.
+5V GND GND +12V
PERIPHERAL DC
POWER CONNECTOR
MAC785
2.If you measure less than 100k ohms between chassis ground and one of
the ground pins on the peripheral’s power connector, you have located a
problem that needs to be corrected. Here are a couple of things to check
for:
a.The four screws attaching the peripheral to its mounting brackets
may be too long. If the screws extend too far into the peripheral they
can come in contact with the peripheral’s signal ground, creating a
direct path to chassis ground.
b.In AM-1400 and AM-1600 computers, if the disk drive mounting
brackets do not have adhesive lexan insulating strips
(DWF-20526-00), it is possible for the drive’s signal ground to be
shorted to the metal mounting brackets.
c.The rotating disks and read/write heads inside your disk drive are
encased in a metal enclosure called the HDA (Head Disk Assembly).
The HDA assembly is tied to the drive’s signal ground. If the HDA
assembly makes metal to metal contact with the drive mounting
brackets in your computer, an AC to DC ground loop may result in
applications where the mounting brackets are directly attached to the
computer’s metal chassis.
d.Review all the mounting procedures discussed in sections 8.X.
There is a separate section for each type of applicable Alpha Micro
computer model.
PDI-00436-20, Rev. A15