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???
03/02/04 23:08
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#65849 - That is not caused by a normal ESD!
Responding to: ???'s previous message
In most cases the VGA chip gets exploded with big crack in the middle like an earthquake has hit it. some times the pins of the vga chip get melted as if a lightning had struck it

Bloody hell, Mahmood, this is not caused by a normal ESD event!! Be very careful, there's something really wrong!!!

Now, I know, why you asked:

Shouldn't there be some sort of fuse in case the BAT54 got fried?

Well, with normal ESD events such a fuse would not be necessary. But what you observe is something much more powerful than a simple ESD event, looks like a surge.

If I added the BAT protectors, would this solve the problem?

I don't think so. BAT54 can very well be used as ESD protection, as you can see in the following link, which contains specifications about BAT54 in ESD tests:

http://www.chrontel.com/pdf/an38.pdf

After you told, that each monitor has its own driver chip, we must think into a totally other direction:
Ok, you stated, that chips are really exploding. Looks like if there's applied a heavy overvoltage to some pin of driver chip. This, in combination with enough energy could indeed cause this heavy damage. But if the only path this overvoltage can hit the vga chip is the monitor cable, then something must be wrong with the monitors.
Assume following situation: You connect one vga driver to one monitor through a cable. If a heavy surge current is flowing from the monitor side to the driver side along cable shield, then voltage drop across cable shield can force a voltage rise of monitor cable ground. If monitor has a protection circuit at its input, this overvoltage is directly injected into the driver output! I mean something like that:



In the schematic I have assumed a voltage drop of arbitrarily 20V. But even voltage drops of about 10V can cause serious damage at vga driver. Transzorb at monitor input subtracts about 1V from this overvoltage if finally a surge current is flowing into the vga driver. As in any case transzorb is much more robust than eventual vga internal 'protection' diodes, most of the overvoltage will drop across the vga chip, but not across transzorb!

Now, where can such a surge current causing this dangerous overvoltage across the cable screen result from? From a loss of protection earth at monitor!
If there are some parts connected from mains voltage terminals to protection earth of monitor, think of filter capacitors from mains voltage filter or even varistors and such stuff, then during the occurence of voltage spikes on mains voltage such parts become charged and a spike current is caused through protection earth connection. But if this connection is lost, then the current will flow over the cable screen to the vga driver!
At power-on moments of monitor, these parts are also charged suddenly and will also cause these dangerous current spikes.

Are there any motors or high inductive loads at your bowling 'application' which could cause heavy overvoltages on mains? Is there a reliable protection earth routing? Have the monitors a good connection to protection earth?
Open a monitor and look what manufacturer has connected from mains terminals to protection earth. This can be very surprising...

Do you see any other possible reason for eroneously applying heavy overvoltages to vga driver pins?

Kai

List of 38 messages in thread
TopicAuthorDate
vga signals isolation problem ( I think)            01/01/70 00:00      
   RE: vga signals isolation problem ( I th            01/01/70 00:00      
      RE: vga signals isolation problem ( I th            01/01/70 00:00      
         RE: vga signals isolation problem ( I th            01/01/70 00:00      
            RE: vga signals isolation problem ( I th            01/01/70 00:00      
            RE: vga signals isolation problem ( I th            01/01/70 00:00      
   RE: vga signals isolation problem ( I th            01/01/70 00:00      
      RE: vga signals isolation problem ( I th            01/01/70 00:00      
         Capacitance - not cable length!            01/01/70 00:00      
            RE: Capacitance - not cable length!            01/01/70 00:00      
               RE: Capacitance - not cable length!            01/01/70 00:00      
               VGA Video            01/01/70 00:00      
      RE: vga signals isolation problem ( I th            01/01/70 00:00      
         RE: vga signals isolation problem ( I th            01/01/70 00:00      
            RE: vga signals isolation problem ( I th            01/01/70 00:00      
   RE: vga signals isolation problem ( I think)            01/01/70 00:00      
   Cable capacitance is not an issue!            01/01/70 00:00      
      RE: Cable capacitance is not an issue!            01/01/70 00:00      
         RE: Cable capacitance is not an issue!            01/01/70 00:00      
            RE: Cable capacitance is not an issue!            01/01/70 00:00      
               RE: Cable capacitance is not an issue!            01/01/70 00:00      
                  RE: Cable capacitance is not an issue!            01/01/70 00:00      
                     RE: Cable capacitance is not an issue!            01/01/70 00:00      
                        RE: Cable capacitance is not an issue!            01/01/70 00:00      
   RE: vga signals isolation problem ( I think)            01/01/70 00:00      
      RE: vga signals isolation problem ( I think)            01/01/70 00:00      
         RE: vga signals isolation problem ( I th            01/01/70 00:00      
         That is not caused by a normal ESD!            01/01/70 00:00      
            RE: That is not caused by a normal ESD!            01/01/70 00:00      
            RE: That is not caused by a normal ESD!            01/01/70 00:00      
               RE: That is not caused by a normal ESD!            01/01/70 00:00      
               RE: That is not caused by a normal ESD!            01/01/70 00:00      
   RE: vga signals isolation problem ( I th            01/01/70 00:00      
      Bowling alleys            01/01/70 00:00      
      RE: vga signals isolation problem ( I th            01/01/70 00:00      
         RE: vga signals isolation problem ( I th            01/01/70 00:00      
         Go bowling, Michael            01/01/70 00:00      
            RE: Go bowling, Michael            01/01/70 00:00      

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