Hello to you all,

I am new to this forum, hopefully I can help some of you guys in the future with my electronics knowledge.

I am looking for a solution to a testing problem that I hope some of you could help on:

How do you test a VGA port on a computer motherboard or VGA card without a monitor ?

 

With the ease of obtaining a monitor, why would you want to test without one? I would suspect the setup required to do what you propose would cost more than a cheap monitor.

 

I am looking for a solution for some automation during pc testing, so I don't need someone looking at the color bar test on the screen.

 

Ok,that makes sense. To bad you don't know anyone who works for NVIDIA. I have no knowledge in that field, so I have no suggestions. That is not to say, someone else might

 

A simple frequency counter should work. Just feed the horizontal and vertical refresh lines into separate counters and you can tell what resolution and refresh rate the monitor is in. I can't think of any practical away of testing the actual image coming out but if you just want an 'alive/dead doing something' If you need something more sophisticated than that you need to tell us exactly what you're testing the output for.

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Thanks, I will give it a try.

Not sure how it will tell me the screen resolution just from the hsync/vsync frequency, can you tell me more ?

Cheers
Cell

 

If you count the number of hsync pulses that come in between each vsync pulse you have the number of horizontal lines at least, on most PCs this can easily lead to the vertical resolution as well. I think they're both ramp voltages (triangle waves) You could possible test R/G/B lines using a test pattern diplayed on the monitor and setting up addition counters on the R/G/B lines that are reset on each horizontal/vertical pulse.

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No the Hsync and Vsync are not ramps.Ramps are put in the coils on the tube.

The Hsync will just pulse on every end of the line and Vsync on the end of the last line. I agree if you used a counter it could verify correct operation. Since in most cases evrythyng works or there is no signal at all.

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Il give you shocking experience.

 

Out of curiosity how does the monitor generate the ramps from the sync pulses?

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It all figures it out from the timings.Because each resolution has its own timing. If your curious how the VGA signal works just try Google it should find some explanations..

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Il give you shocking experience.

 

Just a guess, but I would think the rising edge of the pulse starts a ramp generator.

 

Well its a bit more complicated than that, the higher the resolution the "steeper" must the ramp be because the horizontal scan must go faster for higher resolutions.

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Il give you shocking experience.