Rory said:
I purchased an eMachines W2040 for $10. As it turns out it won't
display video. I can boot it up (I think) but the monitor receives no
signal. I tried a different monitor and still no signal. Then I
noticed that the original eMachines monitor has the #9 pin missing. I
am wondering if this broke off in the connector on the motherboard and
was then forced into the slot by my trying a different monitor with a
# 9 pin in place. Could there be another easily solved answer to this
problem? If I have to replace the motherboard what would be a
compatible one? The video is integrated if that helps. Any help would
be greatly appreciated.
I wasn't able to find a nice tutorial, and only found scraps.
The history of VGA is kinda recorded here. It looks like originally,
resolution info was signaled by static ID pins. At some point, the VESA DDC
added the ability for the host to read the monitor's characteristics,
via a serial interface. Inside a modern monitor, there is a serial EEPROM,
with an I2C interface (serial clock and data). Pin 9 is supposed to be
a source of +5V, flowing from the host to the monitor, giving one
milliamp to read the serial EEPROM.
http://www.epanorama.net/documents/pc/vga_bd15.html
So, when a video cable is missing pin 9, the cable would be from
another era, before DDC/EDID. It means the host cannot determine
the resolution options of the monitor, at startup, if the monitor
is turned off. Presumably, once the monitor is turned on, it
could supply its own +5V. And of course, if the monitor does not
support DDC, the computer can send all the clock signals it wants
on the DDC interface, and there would be no answer.
The computer could try to put out 640x480, assuming it has detected
that a cable is connected to the RGBHV (red, green, blue,
horizontal_sync, vertical_sync) signals. So I would not necessarily
conclude, that because pin 9 (key) is missing, that it is a broken
pin. It could mean the monitor is pre-DDC, and does not support the
DDC function. But computer systems still have to support such
monitors, and missing pin 9 should not prevent the setup from
working.
My old CRT (Sony Trinitron) had an RGBHV coaxial interface, and
an RGBHV to VGA adapter cable. So that monitor would not have had
any fancy DDC on it, and it still worked with the computers I plugged
it into. I believe I've even used that monitor on the computer I'm
typing on, when I built this computer.
This would be the modern definiton of the pins:
http://www.hardwarebook.info/VGA_(VESA_DDC)
This pinout is a mix of the old and new. Here is an example
of mention of pin 9 being "missing" and used as a key. (I.e. Not
likely to have just broken off, but done on purpose.)
http://www.cabletechguide.com/Technical Articles/VGA Pinouts.htm
This is a standards body for computer display output -
http://www.vesa.org/FAQ/standardsFAQ.htm#DDC1
Hope that helps somewhat,
Paul
