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Q: AsusTech : agp 8x video issues

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Old December 10th 04, 10:26 AM
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Default Q: AsusTech : agp 8x video issues

In article , wrote:

Asus P4P800 Deluxe -

Within 1 year I have "RMA'd" 2 brand new retail "8X" video cards, one
nvidia and one ati...both developed boot display annomylies and video
coruption in windows...

A third agp "8X" nvidia card will not run properly on this board,
locks, lags etc...but it runs flawlessly on my "P4PE" agp "4X" board.

I am running an agp "4X" card now and so far things are fine

Q: Is there any record of problems with "AGP 8X" slots on any of these
Asus products ? Possibly some bad circuit, capasitor or the slot
itself which may be specific to the "AGP 8X" feature ?

My new "RMA" replacement card is here, but I will not install it
untill I get some info or you get your board back...


-retail Antec PSU
-retail APC UPS
-tested with all periferals disconnected
-tested full load with agp "4X", OK so far...(3rd week)

Thanks for any response

There is a power circuit on the motherboard that makes
1.5V for the AGP 4X/8X slot. The circuit remains at 1.5V
nominal, whether the slot runs at 4X or 8X. Both the I/O
pads on the GPU (video card chip) and the Northbridge
AGP pads, are powered by this supply.

You've probably read references to AGP using 0.8V . The way
that works, is when operating in 8X mode, the AGP lines are
terminated with load resistors. The resistors cause the
signal voltage to drop to 0.8V, while the I/O pads driving
them are still actually powered by 0.8V. In a sense, this
is still powering by 1.5V, but you'll still see references
to 0.8V, even though the circuit is not fed by 0.8V.

The power consumed by the I/O circuits increases, when you
are running 8X. If the motherboard had a defect in the power
circuit, and could not handle the load of running at the
8X setting, that could cause flaky operation.

You could go into "Advanced" in the BIOS, and somewhere down
there, you'll find "AGP VDDQ Voltage". It varies from 1.5V
to 1.8V, in 0.1V steps. If you put your AGP 8X card back
in there, you could try adjusting the voltage, and see
if a higher voltage makes things more stable. (Don't be
deceived by the BIOS settings - sometimes circuits like
this really only have a high and a low setting. They may
not in fact have four voltages values in actual hardware.
One Asus motherboard is like that on DIMM voltage - there
are really only two DIMM voltages.) Try 1.8V and see if
the 8X card you've got now becomes more stable. It shouldn't
really need a voltage boost like this, but the improvement
in stability could mean that when set to 1.8V, it might
just be barely making 1.5V or something.

There are two supply voltages that could be shared by the
video card and the motherboard - Vagp and +3.3V. And, either
the +3.3V could be coming direct from the power supply, or
the +3.3V could be made on the motherboard itself. Generally,
the other voltages, like +5V or 12V, are converted by
switching circuits on the video card, into voltages that
can be used by the chips, like, for example, the memory
chips for the GPU. As such, an out of spec +5V or +12V is
not likely to fry the video card, as the conversion circuit
on the video card will have some tolerance to voltage error.
But a Vagp error, like if the Vagp was producing more voltage
on the motherboard than it was supposed to, could lead to
the premature death of either the motherboard Northbridge or
the video card GPU.

Does your Northbridge run hot ? That might be a sign of
an over-voltage problem.

I'd recommend measuring some of the voltages on the board,
but am embarrassed to say that I haven't been able to positively
identify many of the power circuits on my P4C800-E (I really
need an oscilloscope for this work, but don't own one). In any
case, to do such measurements, you'd have to pull the motherboard
out of the case, and sit it on the bench.

Considering the problems you've had so far, you should consider
either taking the motherboard to a repair place, and have them
see if they can find Vagp and measure it. Or RMA the motherboard
and take your chances with another one. I hope Asus will believe
you, if you report the cause for returning the board is
"fries video cards" :-)

Old December 11th 04, 11:45 AM
external usenet poster
Posts: n/a

In article , wrote:

On Fri, 10 Dec 2004 05:26:44 -0500,
(Paul) wrote:

In article ,

Asus P4P800 Deluxe -


Wow, thanks for all the tech info paul, I can definately use much of
that information for further annalysis.

I have monitored the 1.5V load thru the bios and with Asus probe, both
seem to indicate similar readings. I cannot be assurred which one is
more accurate, however.
But...both indicate a drop of only .12V without load and of course
this fluctuates to minor positive incriments as well. I wish I would
have tried the voltage adjustment in the bios when the working
replacement card #1 was running so bad in this board... I have seen
this setting. I probably will try it anyways...

Now, just to add the monkey wrench, the northbridge does seem warm. In
fact, during my trouble shooting, I could feel the warmth, not
neccessarily heat, comming from my open chassis. This was pinpointed
to the northbridge chip. Incidently, I ordered 2 stock P4 intel boards
for back up measures and the northbridge heatsinks are twice the size
of the Asus heatsink.

But in relation to:

The way
that works, is when operating in 8X mode, the AGP lines are
terminated with load resistors. The resistors cause the
signal voltage to drop to 0.8V, while the I/O pads driving
them are still actually powered by 0.8V. In a sense, this
is still powering by 1.5V, but you'll still see references
to 0.8V, even though the circuit is not fed by 0.8V.

This point may be the clue, but...

Is this feature done on mobo or on the card ?
If it is done on mobo, then if the load resistors are in fact not
dropping the voltage to .8V, what would that mean ? Unless I am miss
interpreting, this would definatly shorten the life of any AGP 8X card
in this board running at 8X...

I must also say that there is no AGP setting in this bios which allows
me to set the AGP "_X" feature, so it is automatic and sets at the
optimum...I guess.

Thanks so much for the feedback.
I am attempting to RMA the board and the new warranty video card is
going in the intel board. I just like to take these hardware issues as
far as I can, technically speaking...



I didn't think AGP voltage registered on the monitor chip.
Would that be Vcore you are looking at ?

The terminators could be inside the GPU. I cannot really be
sure, as the AGP standard does not address how the AGP
I/O is actually built by companies like ATI and Nvidia.

The termination resistors are there to make a clean looking
trapezoidal signal. The fact that the signal swing is reduced,
does a couple of things. It can reduce the emissions caused
by the switching noise, and a reduced swing signal switches
faster. The termination scheme, in fact, speeds up the signals
two ways. The amplitude is reduced, so the signals don't have
to go as far. And, a parallel termination type, also removes
the RC delay associated with series damping type terminations.
But that is a tiny number, like 250pS or so. (And with the 8X
rate, the clocking methodology is probably such, that delay is
immaterial anyway. I haven't read up on how the clocking works.)

To try to detect the heat, you would need to run the motherboard
first in 4X mode, measure the Northbridge temperature, then
run it in 8X mode. Otherwise, it will be tough to tell the
difference between the two standards.

If I was looking at this, I would need to get out a
multimeter, and find a place to monitor the AGP voltage
on the motherboard. I would get a copy of the AGP standard
and find out which pins on the socket have the AGP I/O voltage
on them. Then, when the motherboard is powered up, probe the
holes along the edge of the motherboard connector, for the pin(s)
in question. But, you have to be very careful when doing
stuff like that, as one slip could short the conversion circuit
for the AGP, and burn it out. (It may not be protected, in the
interest of saving money for Asus.) You should only try this
with the motherboard sitting on the test bench. Clip the multimeter
ground onto a connector lug on the I/O connectors, so the
ground probe doesn't get in the way.

As the AGP standard is no longer on the Intel download site,
I use this one. Page 50 has the pinout, and the AGP voltage
is on the pins labelled Vddq1.5


Page 63 shows a picture of the signal amplitude (0.8V)
compared to the voltage used to power the I/O pad (vddq1.5).

On page 64, you can see a FET being used on the receiving
chip, as a resistor to ground. That FET, is how the chip
is able to digitally control the terminator. The terminator
is not always enabled, and would be disabled when the card
is set to 4X mode. In that case, the signal swings to 1.5V,
and the power for the I/O pad is still 1.5V. (If the AGP
I/O is bidirectional, there are probably terminators in
both the Northbridge and the GPU - two instances of the
circuit, pointing in different directions.)

As far as the Northbridge temperature, other things that
affect it, are running the DDR RAM at DDR500. Or boosting
the DDR voltage, as the voltage used to run the memory,
also runs the Northbridge. The Northbridge and memory
DIMMs share common I/O signals, and generally that means
the I/O power for the two devices will be common as well.

Even dual channel versus single channel, makes a marked
difference in the operating temperature.

Looking at the AGP I/O signals themselves, would be
pretty hard without some fancy test equipment. The AGP
I/O runs at 533Mb/sec in 8X mode, and that means a
5GHz digital sampling scope would be needed, for single
shot capture. You would probably end up capturing an
eye diagram for the I/O, rather than trying to track
the 1's and 0's. Ah, the good ole days...

Old December 14th 04, 06:31 AM
external usenet poster
Posts: n/a

In article , wrote:

On Sat, 11 Dec 2004 06:45:31 -0500,
(Paul) wrote:

In article ,

On Fri, 10 Dec 2004 05:26:44 -0500,
(Paul) wrote:

In article ,

Asus P4P800 Deluxe -



Ya, so the monitors I am reading are what is supplied to the
slot...and I am running in dual channel mode as well.

Even if I did get a reading off of the slot, what would be an
exceptable votage drop? But even if there was a voltage drop, I guess
it would explain the one card choking. Which still leaves the question
as to why the cards are failing after an average of...4.5 months ? If
this were the case, than the tolerance's on the GPU to reduce the
voltage are not able to handle the possible fluctuations of the power
supply, which maybe over the threshold allowed anyway...yes ? Hmmm...

If time allows it, I will try to monitor the voltages as you described
and I am going to purchase a new psu for safe measure.

Your explanations seem very technical, which would indicate to me you
are in a field of electronics. I certain appreciate the challenge of
deciphering through your replies...



There are multiple VDDQ_1.5 pins, so there really shouldn't
be a measureable drop caused by the connector. What you see
on the card side should be the same as the copper on the
motherboard that carries the 1.5V power.

Chips are intolerant to too high a voltage. Too low a voltage
should just result in the board crashing or applications
erroring out (like a 3D game quitting unexpectedly). With
too high a voltage, the circuit will still function properly,
but it will be under a life shortening stress.

I still think you aren't going to know for sure what is going
on, without measuring at the socket, as at least there, you've
got a pinout in the AGP30 spec to work with. A supply problem
is certainly the easiest to visualize as the source of the
trouble, but even one messed up signal on the interface could
do it. That is why, at some point, an RMA might be the only
way to solve the dilemma, and give you some peace of mind.


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