I've just put in a new AT power supply all went well until I powered on. The hard drive started making a contnuous scratching sound. It's a WD Caviar 15.3. I checked the connections and I discovered that it was on the same lead as the CPU fan. I gave the harddrive its own lead and it's been running fine ever since.

When the drive shared the lead with the 12V case fan, while using the old power supply, there was no problem.
Does the 12V CPU fan draw that much power or is it the lead I should be worried about? Is this a common occurrence?

I don't think it would cause this problem. At least I've never encounter it after assembling and modifying quite a few systems.

If you don't have one already, you might get a hardware monitoring utility and watch the voltages. Motherboard Monitor -- http://mbm.livewiredev.com/ -- is excellent (and free), but I don't know if it will work with your system. You'll have to check.

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sleddog (http://www.sleddog.f2s.com)
Pulling for a SmartLabrador (http://www.labradorit.nf.ca/smartlabrador/)

The fans do not draw much power. It is more likely a loose connection of one or more pins on a power connector. I have had to replace a few poor quality "power splitters" that were attached to CPU fan leads.

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reido@my-deja.com