I find that I need to reply to the "coil whine" issue. In my experiences as an electronics technician (for a western Canada electronics control manufacturer), I have found the coil whine can be attributed to many things.
I would assume these PSU under review are designed to the ATX form factor (http://www.formfactors.org/developer/sp ... atx2_1.pdf
) and/or are ATX P4-rated.
A breif PSU design overview:
The PSU design is, as I mentioned in another article (Thermistors for Fans), a switching power supply. Such a switcher operates at around 40,000 Hertz. This frequency is above the human hearing range and should be inaudible.
This means the transformers inside the PSU operate at this high frequency. However, the coils are designed to store the energy from the PSU outputs, should be 'seeing' pulsed DC from the PSU outputs and not reacting to the high frequency. Any noise eminating from the PSU (other than the fan) would be heard as a whine (high-pitched vibration).
Therfore having said all this, the possibilities for coil whine could include:
1) Inefficient PSU design.
2) Defective coils or transformers. The whine could be caused by loose or damaged ferrite cores, or loose wire windings around the ferrite cores.
3) The PSU does not have the required capacity for intended loads.
One sure way to isolate where the noise is coming from, is to use a trick I learned during automotive classes in high school (more than 30-years ago). Take a metal screwdriver (any blade), carefully place the blade on the suspect noise maker and place the handle next to your ear. The noise will travel up the screwdriver and can be easily heard in the handle. This is an easy diagnostic tool to determine which part is making the most noise.
Of course, the PSU is fully operational and the cover is removed. Extreme caution needs to be exercised as there are very high voltages and currents in the PSU. If you use the screwdriver trick, I would highly recomend wrapping the exposed metal shank with electrical tape.
If the whine is caused by the transfomers, nothing can be done (except to replace PSU). However, most coils have some form of glue or epoxy on the outside of the wire windings. The intent of the glue or epoxy is to reduce or eliminate the vibrations within the coils. If the coils do not have the glue or epoxy, you could try that.
Be wary when applying glue or epoxy: too much could cause the coil to overheat, too little will not reult in any effect. A tight balancing act!
Failing all this, you might consider contacting the PSU vendor for a resolution.
Two other topics:
A) When a manufacturer or vendor sends (the company I work for) components for evaluation, I always ask for at leats 5 devices, from various manufacturing batches to fairly evaluate the products. Albeit, the components that are sent can be small components, such as switches, LED's, power supplies (linear & switchers) and larger devices such as LCD modules, input & output modules, etc.
I can appreciate that computer PSU manufacturers will be inundated with requests to supply sample products from all kinds of testing organizations. In the industry that I have worked in (over 25-years), the company I am employed by is an industry leader in innovative products.
Our vendors are ALWAYS inundating us with TONS of sample parts and is in the vendors best interests for keeping companies like (the one I work for) up-to-date with technolgy. These components or assemblies are write-offs from a sales perspective, but could lead to future sales and industry acceptance.
In the long and short of it: the PSU manufacturers / vendors should be providing adequate samples to make reasonable assesments. In all honesty, I doubt if I could evaluate a component based upon one sample.
B) Has anyone seen a PSU manufactured with the optional 6-pin wiring connector (per the ATX specifications version 2.1)? On pages 22 & 23 of this specification, pin 2 (FanC) can control the PSU fan. It would be easy to develope a small switch with resistors to attach to this connector.
Good luck and good computing.