WinTV KB - DVB-T stutters on nForce2 motherboard whilst typing

Symptoms

When a PCI TV tuner is used with an nVidia nForce2 motherboard, stuttering of DVB-T reception may be seen whilst typing with a PS/2 keyboard. The problem does not occur when using a USB keyboard or when using a USB TV tuner. Popping or crackling sounds may also be apparent from the sound card output.

↑ Back to top

Cause

Some nForce2 motherboards with the MCP2 and MCP-T south-bridge experience delayed interrupts when operating in APIC (not ACPI) mode when Spread Spectrum is enabled. In this configuration, interrupts might be delayed or they might be missed completely.

nVidia have confirmed that this affects the MCP2 and MCP-T south-bridge and has been fixed in the MCP-S and MCP-RAID used on later nForce2 motherboards. This problem does not affect the nForce3 or later.

↑ Back to top

Resolution

Solution 1 - Disable AGP/PCI/FSB Spread Spectrum via motherboard BIOS

If your motherboard's BIOS gives an option to disable Spread Spectrum, set all options to Disabled. On some motherboard BIOS (e.g. Biostar M7NCD) it is not possible to disable Spread Spectrum directly but it can be set by changing the FSB to +1MHz higher than default and then back to normal FSB setting. For example on an Athlon XP Barton core with a 166MHz FSB, increase the speed to 167MHz and back to 166MHz.

Solution 2 - Disable APIC and reinstall Windows

If you want to reinstall Windows, you can disable APIC in the BIOS. If you attempt to disable APIC without reinstalling Windows, your system will not boot.

Solution 3 - Disable APIC by changing HAL

This solution might not work if you have the nVidia SW IDE driver installed, and there is a risk that Windows may become un-bootable after changing the HAL. If you want to proceed, follow these steps:

Go into Device Manager
Expand Computers and double click on ACPI Uniprocessor PC
Select the Driver tab and then click on Update Driver
If you get a message asking whether to check online at Windows Update, select No, not this time
Select Install from a list or specific location (Advanced)
Select Don't search. I will choose the driver to install
Select Advanced Configuration and Power Interface (ACPI) PC
Reboot when prompted
Once Windows has successfully rebooted, you can go into the motherboard BIOS and set APIC to Disabled.

Note: APIC and ACPI are NOT the same thing. ACPI is related to Power Management. APIC is related to Interrupts.

Note: If you have the nVidia SW IDE driver installed (particularly version 2.6) you may have an unbootable system if you make this change, although it hasn't been confirmed by nVidia. Due to numerous problems with this particular version of the SW IDE driver (included with nForce drivers 5.10) I'd recommend avoiding installing it altogether and sticking with the standard Microsoft IDE drivers.

Solution 4 - Use USB Keyboard

A workaround for the problem is to use a USB keyboard rather than PS/2. This not resolve the problem with APIC, it simply prevents the problem trigger.

↑ Back to top