Power supply failures

A procedure to identify and troubleshoot the power supply failure based on the most common symptoms:

• Uncommanded hard drive recalibrations
• Windows Event Log data (Event ID 9 from "atapi")
• Low overall performance

The hard drive may shut down and restart on its own with a typical spin-down-click-spin-up sound (readily identifiable once you hear it). The machine will freeze for a short while (about up to ten seconds until the disk restarts). Once the drive is back online, normal operation will be resumed in most cases (barring possible network communication loss and reconnection caused by the timeout).

The analysis of the System Event Log may yield some additional information. The Event Viewer is available via "Start" -- "Control Panel" -- "Administrative Tools" -- "Event Viewer"; once there, open the "System" log. The log may contain multiple entries similar to the following example

Type	Error
Source	atapi
Event ID	9
Description	The device, \Ide\IdePort0, did not respond within the timeout period

Note that port numbers depend on the system configuration.

The hard drives may fall back to the legacy PIO (Programmed Input/Output) access mode. PIO mode is fairly slow and imposes an excessive processor load. Evident symptoms include

• Overall performance low.
• System response "jerky", even for a simplistic tasks.
• Video playback is not possible (frame rates low, down to less than one frame per second in extreme cases)

To verify the drive mode,

1. Open the Device Manager (right click "My Computer", select "Manage", then navigate to "Device Manager").
2. On the right-hand panel, double click "Primary IDE channel" under "IDE ATA/ATAPI controllers".
3. In the window appeared, switch to the "Advanced Settings" tab. This yields a window similar to the screenshot below.
4. Make sure "Transfer Mode" is set to "DMA if available" on both devices.
5. "Current Transfer Mode" should read "Ultra DMA Mode X" for all the installed devices. Hard drives are typically running in UDMA 4 or UDMA 5, CD and DVD drives typically use UDMA 2.
6. Repeat steps 2-5 for the "Secondary IDE channel" if available.

IDE drives in PIO mode

"PIO Mode" readout (as illustrated above) indicates that drives cannot reliably communicate with the controller using DMA modes. The system detects communication problem and degrades drives to PIO mode.

• If one of the above symptoms exists, check the other two.
• If positive on all three, consider replacing the power supply unit (PSU). You may want to temporarily install a known-working PSU from the other system to see if it rectifies the problem.
• Once the power supply unit is replaced, open the Device Manager and uninstall all the disk drives and IDE controllers, then reboot. Windows does not switch back to UDMA mode unless the affected devices are re-detected and re-installed.
• Run CHKDSK on the affected volumes to take care of any possible problems caused by transient drive failures.