dell P3 电源

Dell proprietary (non-standard) ATX design

If you currently own or are considering purchasing a desktop system from Dell you will definitely want to pay attention to this section. There is a potential booby-trap waiting to nail the unsuspecting Dell owner who decides to upgrade either the motherboard or power supply in their system. This hidden trap can cause the destruction of the motherboard, power supply or both! OK, now that I have your attention, read on

As those of you who have attended my seminars or read previous editions of this book will know, I have long been a promoter of industry standard PCs and components, and wouldn't think of purchasing a desktop PC that didn't have what I considered an industry standard form factor motherboard, power supply and chassis (ATX for example). I've been down the proprietary road before with systems from Packard Bell, Compaq, IBM and other companies that used custom, unique or proprietary components. For example during a momentary lapse of reason in the early-'90s I had purchased a Packard Bell system. I quickly outgrew the capabilities of the system so I thought I'd upgrade it with a new motherboard along with a faster processor. It was then to my horror that I discovered that LPX systems were non-standard and due to riser card differences, there was virtually no interchangeability of motherboards, riser cards, chassis and power supplies. I had what I now refer to as a "disposable PC". The kind you can't upgrade, but have to throw away instead. Suddenly the money I thought I had saved when initially purchasing the system paled in comparison to what I'd now have to spend to completely replace it. Lesson learned.

In a similar experience, I remember paying over $950 to IBM parts for a replacement 114W power supply to fit my PS/2 P75 luggable which had a power supply failure out of warranty. The supply had a totally unique shape and a weird connector I had never seen before, and there were no alternative choices available from any other companies. The system wasn't even worth that much at the time, but I was using it for work and had no choice but to pay the price to get it replaced. And of course the replacement was the same relatively low output 114W unit, as there were simply no other versions available that would fit. Another lesson learned.

After several upgrade and repair experiences like that I decided never again would I be trapped by systems using proprietary or non-standard components. By purchasing only systems built from industry standard parts, I could easily and inexpensively upgrade, maintain, or repair the system for many years into the future. I have been preaching the gospel of industry standard components in my seminars and in this book ever since.

Of course building your own system from scratch is one way to avoid proprietary components, but often that route is more costly in both time and money than purchasing a pre-built system. And what systems should I recommend for people who want an inexpensive pre-built system, but one that uses industry standard parts so it can be inexpensively upgraded and repaired later? While there are many system vendors and assemblers out there, I settled on companies like Gateway, Micron and Dell. In fact those are really the three largest system vendors that deal direct, and they mostly sell systems that use industry standard ATX form factor components in all their main desktop system product lines. Or so I thought.

It seems that starting after September of 1998 Dell defected from the cause of industry standardization and began using specially modified Intel supplied ATX motherboards with custom wired power connectors. Of course they also had custom power supplies made that duplicated the non-standard pinout of the motherboard power connectors.

An even bigger crime than simply using non-standard power connectors is that only the pinout is non-standard, the connectors look like and are keyed the same as is dictated by true ATX. There is nothing to prevent you from plugging the Dell non-standard power supply into a new industry standard ATX motherboard you installed in your Dell case as an upgrade, or even plugging a new upgraded industry standard ATX power supply into your existing Dell motherboard. But mixing either a new ATX board with the Dell supply or a new ATX supply with the existing Dell board is a recipe for silicon toast. How do you like your fried chips, medium or well done?

Frankly I'm amazed I haven't heard more about this, since Dell is second only to Compaq in worldwide PC sales. I can only imagine that it is because they started using these non-standard boards and power supplies in late 1998, and most of those systems haven't yet come due for motherboard upgrades. However they are now passing 2 years old, which is about the time that many consider motherboard upgrades. That is why after discovering this information I wanted to make it well known, I figure by getting this information out as soon as possible I can save thousands of innocent motherboards and power supplies from instant death upon installation.

If you've already fallen victim to this nasty circumstance, believe me, I feel your pain. I discovered this the hard way as well; by frying parts. At first I thought the upgraded power supply I installed in one of my Dell systems was bad, especially considering the dramatic way it smoked when I turned the system on, I actually saw fire through the vents! Good thing I decided to check the color codes on the connectors and verify the pinout on another Dell system by using a voltmeter before I installed and fried a second supply. I was lucky in that the smoked supply didn't take the motherboard with it, I can only surmise that the supply fried so quickly it sacrificed itself and saved the motherboard. You may not be so lucky, and in most cases I'd expect you'd fry the board and supply together.

Call me a fool but I didn't think I'd have to check the color coding or get out my voltmeter to verify the Dell "pseudo-ATX" power connector pinouts before I installed a new ATX supply or motherboard. You'll also find that motherboard and power supply manufacturers don't like to replace these items under warranty when they are fried in this manner due to non-standard connector wiring.

I spoke with one of the engineers at a major power supply manufacturer, and asked if there was a valid technical reason (maybe some problem in the ATX specification) that would require Dell to use unique connector pinouts. Of course the answer was that, no, the only reason we could imagine they did this is to lock people into purchasing replacement motherboards or power supplies from Dell. In fact what makes this worse is that Dell uses virtually all Intel boards in their systems. One I have uses an Intel D815EEA motherboard, which is the same board used by many of the other major system builders, including Gateway, Micron and others. The same except for the power connectors that is. The difference is that Dell has Intel custom make the boards for Dell with the non-standard connectors. Everybody else gets virtually the same Intel boards, but with industry standard connectors.

Table 21.7 and 21.8 show the non-standard Dell Main and Auxiliary power supply connections. This non-standard wiring is used on Dell systems dating from after September 1998 to the present.

Table 21.7 - Dell proprietary (non-standard) ATX Main Power Connector pinout (wire side view)

Color	Signal	Pin	Pin	Signal	Color
Gray	PS_On	11	1	+5V	Red
Black	GND	12	2	GND	Black
Black	GND	13	3	+5V	Red
Black	GND	14	4	GND	Black
White	-5V	15	5	Power_Good	Orange
Red	+5V	16	6	+5VSB (standby)	Purple
Red	+5V	17	7	+12V	Yellow
Red	+5V	18	8	-12V	Blue
KEY (blank)	-	19	9	GND	Black
Red	+5V	20	10	GND	Black

Table 21.8 - Dell proprietary (non-standard) ATX Auxiliary Power Connector Pinout

Pin	Signal	Color
1	Gnd	Black
2	Gnd	Black
3	Gnd	Black
4	+3.3V	Blue/White
5	+3.3V	Blue/White
6	+3.3V	Blue/White

At first I thought that if all they did was switch some of the terminals around, then I could use a terminal pick to remove the terminals from the connectors (with the wires attached) and merely reinsert them into the proper connector positions, allowing me to use the Dell power supply with an upgraded ATX motherboard in the future. Unfortunately if you study the Dell main and auxiliary connector pinouts I've listed here and compare them to the industry standard ATX pinouts listed earlier, you'll see that not only are the voltage and signal positions changed, but the number of terminals carrying specific voltages and grounds has changed as well. It would be possible to modify a Dell supply to work with a standard ATX board, or to modify a standard ATX supply to work with a Dell board, but you'd have to do some cutting and splicing in addition to swapping some terminals around. Usually it wouldn't be worth the time and effort.

If you do decide to upgrade the motherboard in your Dell system (purchased on or after 09/98)_then there is a simple solution, just make sure you replace both the motherboard AND power supply with industry standard ATX components at the same time. That way nothing gets fried, and you'll be back to having a true industry standard ATX system. If you want to replace just the Dell motherboard, you're out of luck unless you get your replacement board from Dell. On the other hand if you want to replace just the power supply, you do have one alternative. PC Power and Cooling now makes a version of their high performance 300W ATX power supply with the modified Dell wiring for about $110. Note that the internals are identical to their industry standard high performance 300W ATX supply (approximately $84), only the number and arrangement of wires has changed.

For the time being, I'm suspending any Dell purchase recommendations until they move back into the fold of true industry standardization. Fortunately others like Gateway and Micron have remained true to the industry standard.

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