Also have a dead box [ WAS: Re: OT: dead box ]

[Michael Powell]

Corey John Bukolt wrote:

> On Sun, 21 Mar 2010 11:23:34 +0000 (06:23 CDT) Chris Whitehouse wrote:
>> When you press the power button does the cpu fan or the power supply fan
>> spin for a moment then stop? That's a sign that something on or plugged
>> in to the motherboard has blown. Unplug things and test again.
>> 
>> Chris
> 
> Just a few days ago, I was helping a friend build a system (with all
> brand new components, I might add) and we had this very problem.  After
> sticking in the CPU and RAM and hooking up and turning on the PSU, the
> green LED on the motherboard turns on.  However, the second the power
> button is pressed, everything flashes for a second, then turns back off.
> The green LED on the motherboard also remains on.  The only way to get
> it to flash again is to turn off the PSU, wait, then turn it back on.
> We tried re-seating everything, to no avail.
> 
> Reading this thread, someone else mentioned beep codes and that if there
> were none, it's most likely a fried motherboard.
> 
> Can anyone else confirm this?
> 
Beep codes may be available, but the nature will depend upon the 
manufacturer and the BIOS. Different manufacturers will produce different 
products. In the bad old days the most common beep codes were designed to 
indicate a video BIOS did not initialize, and then the main area of codes 
indicated something wrong in the memory subsystem. Pretty much if they made 
it past these two points the board would boot. And, of course, you need a 
speaker hooked up which I commonly don't because I don't want any beeps.  

One thing to be aware of with regard to modern day motherboards and power 
supplies. I don't recall the exact standards nomenclature, but they are 
spelled out in a spec. Modern day motherboards will have a main power 
connector with either 20 or 24 pins. Some are wired so that a 20 pin power 
supply cable can only go into some of the pins of a 24 pin connector, 
leaving 4 open. Some power supplies have a split cable which has a 20 pin 
and a 4 pin that can be hooked together and will occupy all 24 pins of a 24 
pin connector.

In either case, there is also another second power connector which is 
usually fairly close nearby to the CPU socket. With slightly older boards 
this will be a 4 pin and newer boards it will be an 8 pin. On older power 
supplies there may be only one 4 pin cable designed to plug into this 
connector. Newer models will usually have a cable that splits into two 4 pin 
plugs, so as to be able to plug both into an 8 pin socket while retaining 
backwards compatibility with the older 4 pin boards.

This second connector goes to a high current 12volt rail within the power 
supply and drives all those 'multi-phase' regulators near the CPU. One thing 
that is consistent is motherboards will not even attempt to boot if this 
second power cable is not connected or cannot supply sufficient amps. Some 
power supplies may even beep or have an LED that flashes red. Overlook this 
and the board will never boot.

-Mike