2.6.8.1 - intermittent unblanking problem on Radeon Mobility 7500

I have an intermittent unblanking problem with a Compaq Evo N800v laptop, running 2.6.8.1 with xorg x11 6.7.0-2 (Fedora Core 2). This occurs from just blanking the screen, I am not shutting the lid.

The screen and backlight correctly turn off after a few minutes. Most of the time pressing any key will bring the display back. On rare occasions, the backlight comes on but there is no data displayed, just a blank screen. Switching back to a text console makes no difference, nothing is displayed. Shutting down X and restarting it makes no difference. Once the display is gone, the only fix is to reboot the laptop.

What diagnostics are worth getting for this intermittent problem? Any useful card registers that can be dumped?

lspci -v

01:00.0 VGA compatible controller: ATI Technologies Inc Radeon Mobility M7 LW [Radeon Mobility 7500] (prog-if 00 [VGA])
Subsystem: Compaq Computer Corporation: Unknown device 004a
Flags: bus master, stepping, 66Mhz, medium devsel, latency 66, IRQ 11
Memory at 88000000 (32-bit, prefetchable)
I/O ports at 3000 [size=256]
Memory at 80380000 (32-bit, non-prefetchable) [size=64K]
Capabilities: [58] AGP version 2.0
Capabilities: [50] Power Management version 2

.config extract. ACPI but no APM. radeon and agpgart modules are loaded but have a use count of 0.

CONFIG_ACPI=y
CONFIG_ACPI_BOOT=y
CONFIG_ACPI_INTERPRETER=y
CONFIG_ACPI_AC=m
CONFIG_ACPI_BATTERY=m
CONFIG_ACPI_BUTTON=m
CONFIG_ACPI_FAN=m
CONFIG_ACPI_PROCESSOR=m
CONFIG_ACPI_THERMAL=m
CONFIG_ACPI_ASUS=m
CONFIG_ACPI_TOSHIBA=m
CONFIG_ACPI_BUS=y
CONFIG_ACPI_EC=y
CONFIG_ACPI_POWER=y
CONFIG_ACPI_PCI=y
CONFIG_ACPI_SYSTEM=y
CONFIG_X86_ACPI_CPUFREQ=m
CONFIG_AGP=m
CONFIG_AGP_INTEL=m
CONFIG_DRM=y
CONFIG_DRM_RADEON=m