"Damo" said:
Hi,
My friend has just bought the above Tyan Radeon graphics card and the card
will not work at all on the system. The RED warning light on the motherboard
is illuminated which is meant to be for 3.3v card's (SiS chipset ones). He's
tried adjusting the dip switchs on the Tyan to force it from x8 AGP to x4
AGP and updated the motherboards BIOS but it still won't work.
Any ideas?
Is the motherboard not that compatible with graphics cards?
Thanks in advance,
Damian
Note - Everything that follows is information that an engineer could
experiment with, to prove or disprove a theory. If you are unfamiliar
with electronics or would be economically impacted by destroying a part
of your computer - stop here.
----------------
There is a circuit next to the AGP slot - the AGP burnout circuit. It
consists of a couple of transistors, some resistors, and the red LED.
What I don't know is what it is actually monitoring.
One form of potential problem, is video cards that have connected VDD
to VDDQ. The VDDQ supply is used for I/O only, and it is a dynamic
supply. The voltage it operates at is determined by the speed the bus will
be running at. A VDDQ of 1.5V is used for 4X and 8X. 3.3V I/O is used
for 1X and 2X (although you can also do 2X at 1.5V, as when a 4X card is
asked to run slower than normal). Even in the AGP 1.0 spec, video card
designers are warned to keep the supplies separate, so I find it hard
to believe that this kind of design error exists. (Certainly, your
9600 won't have this problem.)
There is a pin called TYPEDET#, which is pin A2 on
the AGP edge connector. That signal is set to a logic 0 or a logic 1. A
logic 0 indicates that the card would like 1.5V. Now, the AGP 2.0 spec
says the TYPEDET# signal should be connected directly to ground, but
the typical manufacturing test engineers at the video card factory will
force the video card designer to place a resistor in the circuit as well.
+------------+
| |
| GROUND |
----- |
--- \ Resistor to
- / keep test engineering
\ happy...
/
|
|
A2 (Typedet#)
So, when a video card is designed this way, the test engineers can
"lift" the TYPEDET (A2) signal to a non-zero voltage, for testing purposes.
The problem comes, when the card is connected to a real motherboard.
If a motherboard pumps current into the A2 pin, in an effort to detect
whether TYPEDET# is logic 0 or logic 1, the presence of the resistor
gives a non-zero voltage. If the intermediate voltage is high
enough, the signal will look like a logic 1.
In the case of a certain Matrox video card, this problem causes the
motherboard to deliver somewhere between 2 and 3.3 volts to the VDDQ
supply. This is not good if the motherboard is not intended to have
more than 1.5V on the AGP I/O.
On an Asus motherboard equipped with the burnout prevention circuit,
the question is exactly what the two transistor circuit is monitoring.
Either it monitors VDDQ (which wouldn't prevent burnout, because by the
time the circuit detected a too-high VDDQ, it would be too late) or
it monitors TYPEDET#. If it detects TYPEDET# sitting higher than GND,
that might be enough to trigger it and turn on the red LED.
ftp://download.intel.com/technology/agp/downloads/agp20.pdf (pg.231)
Here is what I'd do if it was my video card and it didn't work, as
you describe:
1) Lay the video card on a table. Visually examine pin A2 on the
connector. See if A2 is connected to a resistor, and the other
end of the resistor goes to ground. This can be verified with
an ohmmeter. Note - this is a critical step - the signal must NOT
run anywhere else. If it does, then all bets are off (i.e. you
cannot try the mod). The signal is supposed to be a status only
signal, not driven by any logic. Since the plan is to short it,
then it is essential that the circuit be exactly as drawn in the
figure above.
2) Measure the resistance of the resistor. If it is in the range of
say 50 to 100 ohms, it was probably placed there by test engineering.
What we need to do is short out the resistor, so it is zero ohms.
If you look at the pinout table in the AGP20 spec above, pin A2 is
TYPEDET# and pin A5 is GND. Using a bare piece of wire, plug a wire
from pin A2 to pin A5, using the holes you can see along the edge
of the AGP slot (visible even when the video card is plugged in).
A picture of how to do one of these is shown here:
http://tipperlinne.com/p2b-ds.htm
Note that you are doing a similar mod, except that the width of the
U shaped piece of wire has to span from A2 to A5, without touching
A3 or A4.
With the shorting wire in place and the video card installed, apply
power to the system, and see if the AGP warning light stays off,
and the PC POSTS.
Other than this procedure, the answer is to find a 9600PRO card from
another vendor, who has properly grounded pin A2 as the spec tells them
to.
Whatever you decide to do, BE CAREFUL. Shorting the wrong thing could
cause smoke or fire - your motherboard could be easily burned. You've
been warned... The only reason I'm posting this is so someone who has
figured out what the problem is with the AGP burnout circuit can either
confirm or deny this theory.
Some of the people who have the problem you describe, seem to have the
problem no matter what is plugged into the board. That implies that the
AGP burnout circuit itself is defective, and in that case, my proposed
(untested) mod is not going to work. If you can find a video card that
will POST in the computer, at that point it would be reasonable to
try the A2-A5 mod using the video card that doesn't work.
Good luck,
Paul
