I got a x86-based firewall, produced by Stonesoft. It has serial interface, but it would be easier to install new operating system if I would get VGA output from the device. I discovered promising looking header on the PCB, labeled "J11 VGA".

It's 10-pin header. I discovered the ground and 5V-lines with multimeter and measured resistance from the other pins against the ground pin. Then I took an oscilloscope and measured every pin. Now I need your help to reverse-engineer these measurements into pin-out of VGA-cable. Any advice is very welcome. If any additional measurement is needed, please write a comment to this question.

Attached image show the results. I marked the pin number on upper left corner. The voltages marked there are peak to peak. I was able to find one pin with video-like signal (pin 9, ~120mV peak to peak). Pin 10 looks like sync, but I'm not sure, and I have no idea what the pin 8 is for..


Cable used for measurements



  • 3
    \$\begingroup\$ pin 8 and pin 10 may be sync (the faster one is HSYNC and the other VSYNC). The "video-like" signal may be "green", it's fairly common for the green channel to include composite sync signals. Given that you don't see any activity on the other pins, maybe monochrome VGA. If driving an older CRT monitor (instead of an LCD), using incorrect sync signals can cause damage. Hopefully you're using a modern LCD display. Without the optional VESA DDC monitor ID signals or the SCL/SDA, the VGA adapter can't know what the monitor's capabilities are, so the display format may not be optimal. \$\endgroup\$
    – MarkU
    Commented Mar 10, 2015 at 9:27
  • \$\begingroup\$ For some simple test hookup the "VGA" may very well be the old original 640x480 style video. You could certainly start with that. \$\endgroup\$ Commented Mar 10, 2015 at 14:41

1 Answer 1


How did you find the ground pin? You should measure resistance against the chassis (when you measure resistance, do it without power to the board). The pin which receives ~0 resistance is the ground pin. The reason I'm asking is that that the resistance you get is weird. I'd expect 3 pins (R,G,B) to have 75 Ohm termination resistance against the ground.

BTW, those pins (3,4,6) that you have not detected any signals in, suggest that there is no video output (if you measured correctly). It may be required to first enable video output somehow, before you go on any further.


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