POST question

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hi all

got a question here with ppl giving various answers

can a mobo with the cpu completely removed produce beep codes?

all info appreciated

 

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just a guess, but thats about the only thing it would do.

It would produce a beep code to indicate that the cpu wasnt found - after all, it doesnt know if you removed it on purpose, or if its lost contact for some other reason.

 

apparently not

 

Damn - I was just about to post the exact same link Ferg - great minds think alike they say

 

Agree - no cpu will just give a code to say there is no CPU.

If you are trying to test for anything else, the use of a POST card such as http://www.lindy.co.uk/pci-32-bit-post-code-diagnostic-card/51250.html may also diagnose other problems.

If you're trying to test the actual cpu then use something like PC-Check : http://www.eurosoft-uk.com/pc_check.htm which can test the cpu from it's own boot disk (i.e. you don't need to have a hard drive or o/s installed).

 

cheers guys

just as i thought but i have "experts" arguing with me that beeps will still be produced

in all my years as tech and running my pc shop i have never heard of beep codes with the cpu missing

thanx again

 

It will depend on the board and the BIOS it's running

For details see :

http://www.pchell.com/hardware/beepcodes.shtml

Hope it helps

 

hi there

cheers bud but i still cannot see any concrete evidence on there that states if the cpu is removed there will be a beep code

maybe ive misread the document

cheers

 

It really will depend on which BIOS it has.

e.g., AMI says :

7 Short Beeps Your CPU broke overnight. Its no good. Either replace the CPU, or buy another motherboard. (will give this more than likely if no cpu too)

But also note :

Unfortunately there are many versions of the Award BIOS, and they are supported not by one company, but by the motherboard maker. Award's website states "Award Software software products are sold to a board or system manufacturer ("hardware vendor"), who customizes them further before selling the system. Award Software cannot supply upgrades for a BIOS that has been subsequently modified by hardware vendors."

So, the mb manufacturer may well customise the BIOS. In that case, you may get a beep if no cpu (I think QDI mb's used to but I'm going back a few years !)

In other words, there is no definitive answer, It will depend on which specific motherboard and the version of the BIOS installed

 

The beeps are normally produced by toggling a port line up and down - the speaker is connected almost directly to that port.

This means that the processor has to be running to do the toggle.

If the processor is missing (or dead) then the BIOS will not be run (nothing to run it) so you will not get a beep.

In all the years I've been dealing with PCs I have *never* had beeps with a faulty/missing processor, and, unless the design of the speaker system is changed, I don't see how it could happen.

Harry.

 

I agree with Harry.. without a CPU there will be no POST, so effectively you have a computer without a brain.. ie it wont function at all, dead as the proverbial dodo.

And in practice, i haven't heard a beep from a PC that doesn't have a CPU. you get a single beep usually as the processor starts up.

 

I've *never* had a system POST a beep code with a missing or gakked CPU. Never. In fact, this is the primary symptom of a dead CPU when you're troubleshooting a boxen that won't boot. There may be some mobos that will, in fact, beep with a dead or missing CPU, but I've never run across one.

 

I disagree I'm afraid.

I have definitely worked with m/b where a beep code will occur for a missing cpu. As stated, QDI m/b from memory (prob early 440LX and BX boards)

 

I have used a motherboard that has a beep code for no cpu.

It's probably some extra logic on the board that tests this not the BIOS.

Andi

 

Ok well then the general consensus is thats it's highly unlikely but in rare circumstances it may be possible with some motherboards, if they have been specifically designed to function to a small degree without a CPU.

 

I think the last time I saw a QDI mobo was around '97.

 

datarunner,

To answer your question, you need to understand the overall sequence of events prior to POST. I'm talking about the power supply and how it turns on in the first place.

Back in the day, the AT power supply and power switch were integrated into the same unit. It was a mechanical switch that closed or opened the circuit for the 110 V or 220 V power coming from the wall outlet through the power cord and into the in to the power supply. Here's a diagram of an AT power supply.




So when you turned an AT power supply on, you closed the circuit permitting the high voltage from the wall outlet to enter the transformer that reduced the voltage of the electricity. So the power switch had complete control of the energy entering the power supply and then the motherboard. Which means the motherboard received whatever power the power supply gave it. Here's a circuit diagram:

Code:

[Wall Outlet]--------o/ o--[33]---[Motherboard]

Legend:
--o/ o-- = Switch
[33] = Transformer

Then, in 1995 Intel introduced the ATX form factor. This form factor applied to both motherboard and power supply. One of the major differences between an AT power supply and an ATX power supply is that the AT power supply had a hard switch and ATX has a soft switch. In an AT power supply, the power control was through the power switch and the motherboard received whatever power it got from the power supply. For an ATX power supply, power control shifted from the power supply to the motherboard. Although probably for safety, there is a hard power switch on ATX power supplies as shown above the power cord connector and the red voltage selector switch and to the right of the fan in the following picture.



Let's assume that the hard switch on the ATX power supply is currently (pun intended) in the ON position. So the only things are the ATX motherboard and the ATX power supply. As previously mentioned, with an AT power supply, the on/off switch controlled the 110V/220V flowing into the power supply. However, the ATX power supply has a secondary circuit that works in conjunction with the motherboard for it's power on/off control. That's where the, relatively safer, low voltage on/off soft switch for most ATX cases are for. So far, we've got a circuit in the power supply waiting for the "power on" signal from the motherboard. So, the question is, what happens when you push the power button on an ATX case? The power button activates the "power on" signal generating circuit of the motherboard to send the "power on" signal to the ATX power supply. However, this "power on" signal generating circuit works in conjunction with the motherboard and CPU. So no CPU, no "power on" signal generation circuit activation, so the power supply is still waiting for the "power on" signal from the motherboard. Since the power supply is still waiting for the "power on" signal, it is currently (pun intended again) in the "off" state. So since the power supply is in it's "off" state, the motherboard isn't receiving full power. Since the motherboard isn't receiving full power, POST won't be run. Since POST won't be run, where would POST beep codes come from?

So in summary (networking pun intended), it depends. For an AT power supply system, since the power supply is providing power to the motherboard and the motherboard is receiving whatever power it is given by the power supply, if the BIOS' POST system is hard coded to emit a POST beep code for "missing CPU" then yes, a "missing CPU" POST beep code would probably be heard. However, with an ATX power supply system, with a missing CPU, the ATX motherboard with the absent CPU wouldn't be able to send the "power on" signal to the ATX power supply, therefore the motherboard wouldn't receive full power, therefore POST wouldn't be run, therefore POST beep codes may not be given. Unless there's a separate non-POST circuit that runs off the ATX power supply's standby power provided to the motherboard that would give some sort of beep code or indication that the CPU is missing. So to answer your question, "it depends."

Source:

1. PCGuide - Ref - Power Supply - Form Factors - http://www.pcguide.com/ref/power/sup/form_AT.htm
2. "ATX" from Wikipedia, the free encyclopedia - http://en.wikipedia.org/wiki/ATX
3. "New Power Supply" webpage at the Ask Bob Rankin website - http://askbobrankin.com/new_power_supply.html