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AMD Llano A8-3850 has strange overclocked VGA bug

Chris Finnamore
29 Nov 2011
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Using a VGA monitor and wanting to overclock your Llano chip? Think again

AMD's Llano A8-3850 processor seems to have a strange bug. While testing a PC with an A8-3850 using the processor's integrated graphics and connected to a monitor over a VGA cable, we noticed that the Windows desktop didn’t fit on the monitor, even though the graphics card was set to output the display's native 1,920x1,080 resolution. The Windows desktop was somehow stretched, meaning the Start bar and clock no longer fitted on the screen.

Windows desktop

Even though the graphics card is set to output the monitor's native resolution, the Windows desktop doesn’t fit - click to enlarge

Further investigation showed the processor to be overclocked; the motherboard's bus speed was set to 120MHz instead of 100MHz for a performance boost. Once we set the bus back to 100MHz the Windows desktop looked normal again. Everything also looked normal when we used the DVI output, with or without the overclock.

It seems that the A8-3850's VGA video output is affected by the overclock. The graphics processor itself isn’t overclocked - we had the same problem when we forced the graphics to run at their native 600MHz speed.

The desktop also didn’t fit the monitor at other resolutions; when playing Dirt 3 at 1,280x720 with the overclock turned on, the image was off-centre, leaving a black bar down the side of the monitor.

Dirt 3

Gaming at 1,280x720 over VGA gave us an off-centre image with a thick black bar on the left - click to enlarge

The PC had an AMD A8-3850 processor and Gigabyte GA-A75-D2H motherboard, but we had exactly the same problem with the same processor and an Asrock A75 Pro4 board. In short, if you're going to overclock your Llano processor, make sure you're not connecting to your display over VGA.

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