After one year of successful firewire miniDV capture, new problem with severe artifacts, checkered blocks, strobing several times per second.

Uninstalled new upgrade VIA Hyperion 4 in 1 version 4.51, and reset bios to default. This forced a reinstall of Nvidia drivers also. DV capture problem solved.

Conclusion: capture problem due to VIA upgrade, or BIOs tweaking. However VIA upgrade solved original problem of no DMA on IDE channels. Now, it's back to PIO only mode.