I have two things:
- PSU with 4.6 - 5.1 Volts on it’s 5V Line
- WD Green 5000AADS
So… is is okay for 5000AADS to be powered from unusual 5V line?
Hello,
Take a look at this link. Hope it helps.
http://wdc.custhelp.com/app/answers/detail/search/1/a_id/1679#
If yours is a PC PSU, then I would replace it, or examine the capacitors on its DC outputs. I would also measure its +12V supply rail. Typical PC PSUs regulate by sensing a weighted average of the +5V and +12V supplies. This means that, if the +5V rail drops, then the +12V rail will be correspondly high. In your case I would expect that when the +5V rail dips to 4.6V, the +12V rail may rise as high as 13V.
That said, I have been unable to find any useful technical document from WD. However, my understanding of WD’s drives is that the +5V rail powers the motor controller IC (eg “SMOOTH”) and the preamp on the headstack. All the other chips are powered from voltages which are generated onboard (Vcore, Vio, V- for preamp), and these voltages can tolerate a wide variation in the +5V supply.
FWIW, the datasheet for one of the original SMOOTH controllers (L7250) states that this IC has voltage monitoring logic which produces an NPOR (Power On Reset) signal when the supply rails are at an acceptable level.
L7250, STMicroelectronics, 5V AND 12V SPINDLE AND VCM MOTORS DRIVER:
http://pdf.datasheetcatalog.com/datasheet/SGSThomsonMicroelectronics/mXyuswx.pdf
The chip’s VCC5 threshold is 4.175V +/- 0.175V and the VCC12 threshold is 9.5V +/- 0.5V.
As for the preamp, I expect that it may also have some voltage monitoring logic that prevents it from writing on the platters if its voltages are not within an acceptable range.
Preamp Block Diagrams:
http://malthus.zapto.org/viewtopic.php?f=59&t=229
For example, here is a preamp with a “fault processor” section that has “low supply detection” logic:
