Editing IBM PC XT Troubleshooting Guide (section)

== MFM Hard Drive Diagnostics ==

The XT's standard 10 MB Seagate ST-412 / Xebec 1210 controller combination, and later 20 MB Seagate ST-225, have well-known age-related faults.

=== Stiction ===

After years of storage, the heads can stick to the platter and prevent the spindle motor starting. Symptom: the spindle hums briefly then stops on power-up.

# Power off.
# Remove the drive from the chassis.
# With the drive vertical and not connected, gently tap the side of the drive (a few millimetres of movement against your other hand) to free the heads.
# Power the drive on its own to confirm it spins up.

=== "1701" at POST ===

The [[IBM Fixed Disk Adapter|Fixed Disk Adapter]] cannot communicate with the drive. Causes in order of probability:

# Loose ribbon cables. Reseat the 34-pin control and 20-pin data ribbons at both ends.
# Drive failure (head crash, electronics failure, spindle motor).
# Failed controller card.
# Insufficient +12 V supply to the drive's spindle motor.

=== "C800 ROM" message at POST ===

The HDD controller's BIOS expansion ROM at address C8000 has a checksum error (or is corrupt past the first two bytes). On the 11/08/82 5160 BIOS this is displayed as "C800 ROM" on-screen and the boot continues. On the 1986-dated BIOSes, the same condition produces a "1 long + 2 short" beep that looks like a video failure — see [[#Known Problems and Issues|Known Problems]] below.