TECH NOTE: Odd Video Artifacts Reveal Memory Corruption
I recently had a customer drop off a laptop that was having very odd issues on the screen. There were all sorts of artifacts scrolling up and down the screen, with an odd checkerboard pattern that changed randomly based on mouse movements or even touching the computer. Sometimes video corruption like this can be a driver issue that is usually resolved by getting the latest drivers for the video card. In this case, however, the corruption persisted even in the bios menu and a boot cd. This meant the issue was in the hardware and not software. Now, hardware video corruption issues are sometimes memory corruption or loose cables. If the cable that connects the laptop’s LCD to the motherboard becomes loose, but not completely disconnected, you can get random corruption on the screen.
I figured it was a cable problem and while I prepared to take the laptop apart I ran my Citronix Remote client from the laptop to diagnose the issues from my desktop when something odd happened. The video corruption persisted even in the VNC connection! Ever stranger was that the mouse cursor was unaffected by the corruption and that certain windows and pop ups would also come in clear.
This meant that it wasn’t a cable issue, but the corruption was occurring in the laptop’s video memory itself. Since the corruption was in memory, when the VNC server sent the contents of the video memory to my lab station, it also copied the artifacts. I turned it off and replaced the ram, but the corruption was still there. This was bad news for my client, as that meant that the laptop had dedicated video ram that is soldered to the laptop’s motherboard. I looked up the laptop model and sure enough, that model had separate dedicated video ram. This type of memory is not serviceable and required a motherboard replacement to fix the problem.
Update: I opened the laptop up to check for physical damage to the memory chip such as a faulty solder joint or the chip being physically compromised in some way. I found no such external damage, but I got a pretty good macro photo out of it
