Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
Paul wrote:
> In article <%x5Jc.6998$sV2.3750@newsread2.news.atl.earthlink.net>, "Lil'
> Dave" <spamyourself@virus.net> wrote:
>
>
>>You need a video card, ram, a PC speaker connected, and a keyboard. If you
>>receive any kind of beep from the PC speaker, the bios exists.
Delete the RAM - if the BIOS is alive, it will complain with long,
repeated beeps.
>><eric@egypt.net> wrote in message
>>news:vrh9f0pnav2kvd9s2q6p1memko90g2jc4i@4ax.com...
>>
>>>This is about an Asus p2b rev 1.10 which I have on my work table at
>>>the moment. No POST. Using a bare minimum of hardware, I've swapped
>>>out everything: memory sticks, cpu's, video cards and hard drives ad
>>>finitum. All the hardware works fine on other boards. The FSB jumpers
>>>are set for 66Mhz which should boot anything I throw at it. (I have
>>>altered these to 100Mhz just for variety, every now and then)
>>>
>>>On this mobo in particular what I get is a whir of fans from the HSF
>>>and the PSU, the hard drive makes noise as if going to boot and then
>>>stops, nothing but a black screen and no further activity. Oh yeah, it
>>>also starts immediately upon being pluged in.
>>>
>>>Does this sound like a dead bios? I could hot swap to find out, but
>>>first looking for opinions.
>>>
>>>thanks, eric.
>
>
> "Oh yeah, it also starts immediately upon being pluged in."
>
> That is not a good sign. On my P2B-S, this happened once when an IDE
> cable was only half installed (I bumped it out of place during
> assembly). Some voltage is being upset when that happens, but I
> doubt I could describe an exact mechanism. In any case, the problem
> you have is more primitive than a BIOS problem.
IME there are any number of problems which can cause "starts
immediately", including improperly seated CPUs, PCI cards, drive cables
etc. - even P2B systems with no problems have been known to do this on
occasion. However, I agree the problem is almost certainly a hardware
failure on the mainboard, especially given the amount of swapping done
with no change in symptoms. (I am assuming PSU was swapped or known
good, although the OP didn't mention it).
> If it wasn't for the "starts immediately" problem, I'd be looking
> for one of the onboard regulated supplies failing, like Vcore or
> some termination voltage etc. These are all tied together into a
> status signal called "Power_Good" or the like. If any supply isn't
> within spec, the processor is never given a chance to come out
> of reset. Debugging a problem like that, isn't easy, as on some
> 440BX boards, four regulated supplies come from the same chip,
> and the status signals are not separately available for each
> voltage. In a properly equipped lab, I would use a four channel
> storage scope, to figure out what is going on.
The fact the CPU fan continues to spin means onboard supplies are
*probably* OK, but a DMM or (preferably) a scope would be needed to
confirm. Electrolytic filter capacitors are rarely a problem on P2Bs,
but they do fail occasionally which is the reason a scope is preferred
for checking voltages - ripple tells the story.
You really need a POST card, DMM, and scope to debug these symptoms.
First look for BIOS activity with the POST card (none expected given the
symptoms, but worth doing anyway). Then check onboard voltages which
don't have corresponding LEDs on the POST card (typically Vcore, Vtt,
and the 2.5v clock chip supply), then FSB and PCI clock signals with the
scope. Finally, verify that Vcc is present at the appropriate pins on
all the major chips - several are protected by zener crowbars close by.
IME ~60% of dead P2Bs pass all the above tests with no problem found, at
which point I conclude the BX northbridge is dead and stick it in the
parts bin - I don't have a storage scope to confirm the diagnosis, but
on the one occasion I had access to a full lab, the storage scope
confirmed it on 6 of 7 boards tested. The other one had a dead hardware
monitoring chip and was fixed, but I'm not sure it was worth the effort
The other ~40% are usually easily repaired - the most common failure
modes are blown FETs (sometimes with colateral damage), tripped
crowbars, and shorted decoupling capacitors.
HTH
P2B
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