Fixing the Fix for a 3dfx Voodoo Card’s Overly Bright Picture

[Diablo]

After previously fixing an overly bright picture from a Voodoo graphics card with a simple resistor on one of the RAMDAC’s pins to correct its faulty internal Vref, [Bits und Bolts] got called out for not taking component drift into account. Thus in an update video he shows how instead to use an adjustable AMS1117 voltage regulator to hopefully prevent either the original issue or something new and exciting from cropping up later.

The basic idea here is to use the external voltage reference (Vref) pin for this ICS5342 RAMDAC and supply it with a constant 1.235V. If unused – as on this Orchid-branded Voodoo card – it is connected via an 0.1 microFarad capacitor to ground. This fortunately means that the pin is routed to easily accessible pads that make this modification relatively straightforward.

Basically this is where the AMS1117-ADJ chip comes into the picture, as a widely available adjustable LDO option, even if the 0.8A current rating is very much overkill for this application. With the supplied voltage the lowest voltage this LDO can output is around 1.25V, which is within the 1.10 – 1.35 V range of the datasheet.

Of course, with the PCB never having had a provision for this part, much of the rest of the video is about planning out where to place and route the components. After that tedious work and testing that nothing explodes, the new voltage is used for the RAMDAC’s Vref pin, fixing the brightness issue.

While one could argue that this RAMDAC is likely simply defective and already beginning to break down inside, this should at least give it a bit longer on what seems to be a little used card anyway.