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how to prevent vga port damage?

Last response: in Graphics & Displays
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February 7, 2007 8:23:49 PM

I recently fried the vga output on my laptop by unplugging my monitor then plugging it back it while both were powered on.

I'm not sure exactly which action fried the vga port. What are the official recommendations to avoid damage to vga components?
(i.e. is it worse to plug or unplug the cable from the vga port?)
a b U Graphics card
February 7, 2007 8:40:21 PM

I've never experienced that nor read about it before.

I've hot swapped a ton of them.
Likely static discharge being the culprit because there's not much juice running on the DB-15 connection, but there's a good deal on the power plug, and a ton inside the monitor itself. Sounds like either static or something faulty.

The only issue I've had even close was when I was 10 taking off my sweater after coming from outside and touching the power plug at the back of an original PC caused a static dicharge that blew the CGA card, but that had nothing to do with the connector itself.
February 7, 2007 11:17:31 PM

was the laptop plugged into the AC?
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February 7, 2007 11:37:43 PM

yes it was.
February 7, 2007 11:45:40 PM

Then the most probable cause was a difference in grounds. That happens when your laptop is on one 'zone' and the monitor is on another, where the AC plugs together? or where they on different walls, far apart or something like that?
a b U Graphics card
February 8, 2007 12:32:57 AM

As an electronics engineer I have encountered this problem before. The reason that the VGA port gets fried is due to the capacitance of the mains transformer in the monitor, as there is no earth to the monitor the metal work floats at half mains voltage with a charge determined by the capacitance of the mains transformer, connecting it to the computer (which is earthed) discharges the charge to ground. The very large pulse of current causes the ground rail to rise above the maximum supply voltage of the DAC chip for a few nano- seconds thus destroying it (the DAC chip is sensitive to over voltage). If you don’t believe me try touching the metal plug from the monitor unconnected from the computer and the computer case and see how high you jump.
Always make sure that the monitor is switched off before connecting it to the computer.
February 8, 2007 8:02:55 PM

A very good explanation there.

I guess the reason the chassis is not grounded thru its own ground is that the chassis is supposed to ground out through the computer? That must be a big risk in using hardware kvm switches then?

I wonder if just powering off the monitor is sufficient to be safe, since the potential may not drop to zero right away after turning it off (due to capacitance in the monitor)?
February 8, 2007 8:23:22 PM

The monitor chassis MUST be grounded and the HT transformer must be grounded as weel it's a security rule in all countries!
If it's not grounded of course there are discharges when you connect the monitor to the PC, but this happens only if you have a poor earth connection on your plug or mains cord or if the monitor is damaged.
This is very dangerous for your health and life, not only for your PC!
February 8, 2007 9:03:52 PM

I just noticed that my laptop is connected to a portable power supply with a 2 prong plug so the laptop isn't grounded.

My LCD monitor has a ground plug though.

At any rate.... turn off the monitor first and I'll be safe?
a b U Graphics card
February 9, 2007 12:22:28 AM

Although the Monitor power supply is grounded on the primary side, the secondary side is isolated and not connected to ground, If you were to ground the secondary side you could get an earth loop which shows up on the monitor as a hum bar moving up and down the screen.
At any rate.... turn off the monitor first and you’ll be safe.
April 14, 2013 10:24:25 PM

redss said:
I just noticed that my laptop is connected to a portable power supply with a 2 prong plug so the laptop isn't grounded.

My LCD monitor has a ground plug though.

At any rate.... turn off the monitor first and I'll be safe?

The above is not viable if it is a laptop and nowadays laptops automatically detect the vga cable which goes to the LCD projector. Now if the problem lies with the cable then you may still destroy your VGA card and if it is integrated with the mother board - you have to replace the whole mother board ... sob sob sob - it happened to my laptop - thank God it is still under warranty

a c 85 U Graphics card
April 14, 2013 10:49:05 PM

It was probably a ground loop where the ground on the monitor is different then the ground on the computer.
I have seen sparks when plugging or unplugging monitors but luckily never fried a port.

Laptops usually have the AC line ground connected to the DC- either directly or through a resistor or capacitor.
!