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VGA output hardware testing device

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New Member
Continuing from a previous thread: Sceadwian, i am just looking for a normal screen output. That is a "suspect VGA card" in a test PC. PC is booted and i look for an output (at the moment i look at a connected LCD monitor). But its not the best option, to carry a monitor everywhere as if my monitor were a briefcase - LOL !

So these H and V sync pulses - do they carry positive DC volts ??? If that be the case, does that not come close to the answer ? Have a look at my crude ansi diagram below:

G+++++++++++++++ LED3
B++++++++++ LED2 -
LED1 - -
LED4 -
H++++++++++++ LED5

If all LEDs light up, the VGA output should be okay ?

For other persons reading - i am trying to create a simple VGA output test device that hooks up to a VGA adapter port (Omit VGA monitor). It just looks for live signals necessary for a normal VGA operation. So far Sceadwian has been kind to offer some advice.


New Member
Sorry, my ansi diagram got messed up after i submitted it.
It is only depicting that all 5 lines - R,G,B,H,V are run through LEDs and connect to a common ground. So if all LEDs light then VGA signal should
(in theory) be good, i assume.

BTW, i am NOT a electronics person, I only understand basic, elementary
stuff in that area.

Thanks, for any additional input.


I don't think a VGA port can source enough current to light an LED directly like that, and if it's not already broken it could damage the VGA card hooking an LED up to it like that. You would also need a screen that was almost completely covered in one particular color to show it. Feel free to try to connect an LED to ground via a 100ohm resistor to one of the RGB lines and see what happens but I wouldn't. You'll get nothing out of the H and V lines the pulses are too short.
If you need this for common testing buy a tester, or hook up a monitor. I have been around computers my entire life, I have never seen a monitor that was damaged from an improperly functioning video card, I'm not even sure it's possible with modern hardware, the monitors shut off the sync signals are out of range.


New Member
Thanks SW:

I am beginning to see where this would not work. As i had mentioned before,
about the "carry-over" of damage, i have seen it happen to other techs and
even myself -with something as simple as a keyboard, damaging a motherboards, etc. So i just wanted to point out my reason for an isolated test VGA tool. LCD monitors are too expensive for me to carry everywhere
and test other peoples' damaged PC. CRTs are even worse, they are too heavy.

I guess i'll work out something.

Thanks again.
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