Chapter 7 Service Notes - Compaq 133756-004 - Deskpro EN - 6550 Model 6400 Maintenance & Service Manual

7
chapter
S N
ERVICE OTES
CAUTION: Use safety glasses equipped with side shields before attempting to clean debris from
under the keys.
1. The processor chip is mounted upside down on a board. The heatsink mounts directly to
the back of the chip. The chip is in the center of the processor package, but the
processor is offset in the system board socket because of the hinge for the lever arm.
The heatsink and clip must be properly aligned so that the clip pushes the heatsink flat
against the chip.
If the heatsink is mounted improperly, the processor runs at a higher-than-normal
temperature and the computer posts an immediate processor failure message (before
the computer completes Power-On Self Test [POST]). If the Compaq DMI software is
installed, the user receives a warning about any elevated temperature in the processor.
2. Unplug the power cord before installing or removing any PCI boards since the PCI slots
have auxiliary power applied. If the power cord is not unplugged, damage to the boards
can occur.
3. Each time the system starts, the system ROM saves a copy of NVRAM (including
CMOS, passwords, and other system variables) in the flash ROM. Should the system
become unstable, the last known good copy of NVRAM can be restored using a feature
called "power button override." To restore NVRAM, do the following:
!
With the unit powered down, press and release the power button.
!
Immediately after pressing the power button (during POST), press and hold the
power button until the unit powers down (about 4 seconds).
At the next startup, the ROM detects this "power button override" event and the backup
copy of NVRAM is restored.
Because of this feature, users cannot power off the computer immediately after powering
up. The video display must be active before the computer can be powered off.
4. The following setup is required for system memory to run at 133 MHz:
!
A 133-MHz front-side bus processor must be installed
!
All installed DIMMs must be PC133
!
No more than four loads on the data lines (four sides of SDRAM)
In all other cases, the system BIOS downshifts the memory to 100 MHz.
Compaq Deskpro EN Series of Personal Computers 7-1