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No image after reset (Tseng Labs ET4000AX)

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First post, by hasat

Posted on 
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Hello,
i have this card with weird behaviour: card runs without problems in DOS or Windows, but after computer reset (from keyboard or reset button), my CRT monitor show me error message "Sync out of range" and image from PC never appear, but PC normally continue booting without image. I must power cycle PC to restore normal function. I think it's something wrong with RAMDAC (Winbond W82C490P-80), my knowledge in this area is not too big.
Any tips what can i try to resolve this problem? Thanks

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Reply 1 of 2, by clb

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Do you have a multimeter with a frequency measure option? One way to start debugging might be to measure the frequency of the HSYNC and VSYNC pins coming out on the VGA cable when the bad frequency is occurring. Is the card outputting any hsync or vsync signal at all, or is it outputting a crazy signal of some sort? Then compare to the good hsync and vsync signals to double check what is different.

Also double check all the caps on the card. Maybe power dips when resetting, and the card goes in a bad state and is unable to resolve itself, or something like that.

Reply 2 of 2, by hasat

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I again tested this card in two different motherboards and it works normally after every reset.
Weird, it's somewhat picky. Maybe some settings in BIOS...
Now is in my main 486 gaming computer and let's see...

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