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View Full Version : Unknown variant of ATI VGA-Wonder 16 distorted video?



Capt. 2110
March 1st, 2017, 09:39 AM
I have a ~1990 ATI VGA Wonder 16 graphics card in my ongoing 386 project, and the image it displays has dark streaks down it every half inch or so, and the image wiggles a little on text portions, and this is on an LCD monitor. I was going to replace the caps, but they have THREE LEGS. Is there anything I can really do to fix it?

Thanks,
Capt. 2110

Stone
March 1st, 2017, 09:49 AM
Is it the same with every monitor you've tried?

Capt. 2110
March 1st, 2017, 09:59 AM
Yes, and with different computers.

Stone
March 1st, 2017, 10:07 AM
If you can't find caps with three legs you can use caps with two legs. Just be careful to observe the correct polarity.

Capt. 2110
March 1st, 2017, 10:21 AM
Okay, cool. Was there a reason they used three legged caps?

Chuck(G)
March 1st, 2017, 10:31 AM
Yes--there's no "wrong" way to insert a 3-legged cap. With a 2-legged cap you have to observe polarity. This mattered a lot when through-hole boards were being manually stuffed--human error could really mess things up. Today, not so much, which is why you don't see them on newer equipment.

modem7
March 1st, 2017, 11:17 PM
Okay, cool. Was there a reason they used three legged caps?
Some three-legged caps, when used within the circuit in a particular way, improve the filtering. See [here (http://minuszerodegrees.net/electronics/capacitor_three_legged_1.png)].

ibmapc
March 2nd, 2017, 11:06 AM
In modem7's example the three legged cap would complete the circuit and a two legger won't work.

Chuck(G)
March 2nd, 2017, 11:20 AM
Sure it will--you just have to jumper the outer pads. A no-brainer. The lead inductance in most cases, doesn't amount to a hill of beans--a few nanohenries at most.

ibmapc
March 2nd, 2017, 11:35 AM
Sure it will--you just have to jumper the outer pads...
I considered that, but it might not occur to some people when replacing a three legged cap with a two legged one that the circuit was left open when one of the outer pads is left unconnected.

Maybe I should have stated:
"In modem7's example the three legged cap would complete the circuit and a two legger won't work without bridging the outer pads on the board."