Failure To Complete Post Sequence - Sony VAIO PCG-V505 Series Training Manual

Failure to Complete POST Sequence

Unlike desktop computers, Sony notebooks do not produce a series of diagnostic "beeps" to aid in the POST
sequence. The only indication of a successful POST is the appearance of the Sony logo on the screen followed
by the operating system splash screen. Certain device failures will prevent the Sony logo from appearing while
others may allow the display of the logo but prevent the unit from beginning the OS loading. Figure 1-3 illustrates
a flowchart to guide you through a POST failure diagnosis.
SONY Logo Does Not Appear:
It is important to verify that a problem does not exist with the LCD display panel. If the hard drive activity LED is
active, the unit has passed the POST stage and is loading the operating system. The problem is likely a failure in
the LCD panel since a defective video driver would keep the POST routine from completing. This is important to
remember because the LCD backlight will not turn on until the end of POST. If is it verified the unit is truly hanging
up at POST with no logo appearing, the following items should be checked:
• RAM: Defective RAM IC's or sockets are the most common cause of POST failures in any computer.
If the unit has dual RAM IC's, remove one of them and see if the unit completes POST. If not, re-insert
the first IC and remove the other. If the unit passes POST, the defective RAM has been located. NOTE:
If either RAM IC is able to complete the POST routine, be certain to try starting the computer with the
functioning RAM by putting it into the other socket. This will eliminate the possibility of a defective socket
having caused the POST hang up. If the unit has only one RAM IC, a known, good IC will need to be
inserted.
• CPU: This is the next likely suspect. Check the CPU to be certain it has not come loose. The only way
to isolate the CPU is to replace it. Be certain to install a new heat transfer pad whenever the heat sink is
removed from the CPU.
• Motherboard: Replacement of the motherboard should be attempted next. Check the Sony ESI website
for the correct board part number based on the model you are repairing. This number will contain a
B prefix instead of an A prefix like most Sony boards. A motherboard with a B prefix will contain the
necessary DMI information for that model. NOTE: Based on previous repair history, motherboards
tend to have a low failure rate. Be certain to double-check any other causes before ordering such
an expensive part only to find that the problem still exists.
• Hard Drive: Although the hard drive is technically not part of the POST, it can hang up the routine,
especially if it is loading the power supply excessively. The unit will complete the POST with the hard
drive removed and will display "Operating System Not Found".
• Video Driver: In many cases the video driver is integrated with the motherboard. In cases where the video
driver is contained on a separate board, it can be difficult to discern whether the driver or motherboard is
the cause. For units that are under warranty, authorization should be requested for both boards.
• Any Other Devices: Modems, LAN cards, Memory Stick®, and any other removable devices should be
disengaged to see if the POST completes.
Service Tip: For units with separate video driver circuits, defective drivers can usually be detected by using
an external power supply, instead of the AC adapter, to power the unit up. The driver board will usually draw
excessive current if defective. A power supply with an amp meter capable of reading up to 8 amps is required due
to the higher power consumption of the newer and faster microprocessors and display panels. The procedure
below is generic and can be applied to virtually any laptop or notebook computer.
Apply power with the external supply set to the normal operating voltage of the AC adapter. Note the amount
of current being drawn at turn on. Turn the unit off and remove the video driver board. Re-apply power, turn
the unit on and note the current draw. If current draw is significantly lower (250ma or more), the video driver is
1. PCG-V505 Series Troubleshooting
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