Troubleshooting a Video Adapter and Computer Monitor
Warning! You must unplug your ATX power supply from the wall before working inside the case.
Copyright 2010 by Morris Rosenthal
All Rights Reserved
The 2nd edition of the eBook can downloaded anywhere in the world for $9.95 or the new 3rd edition of the book can ordered from Amazon for $17.00, or from Amazon UK for £13.95 or through any retail store by the title "Computer Repair with Diagnostic Flowcharts Third Edition" or ISBN which is: 0-9723801-8-3.
Video Card Problem
Note that these steps correspond with decision points on the flowchart and are reached directly by clicking on the diamond symbols. The text below cannot be read sequentially.
Is the system power coming on? Can you hear fans turning and drive motors spinning up, see little lights on the front of the CPU case, hear any beeps? We're talking about system power here, not the monitor power. If the system isn't powering up, or if you aren't sure whether or not it is, go to the Power Supply Failure chart now.
Does anything at all show up on the screen with the monitor power on, or is it just as black as before you powered on the CPU? We aren't demanding any signs of intelligent life in this case, any sign of life will do.
Assuming the system power comes up, does the monitor power come on? Monitors have a status LED on the front bezel that should show green, orange, or blinking if the monitor is powered on. You can also hear older monitors power on with a gentle sound, though I can't describe it beyond saying it's the sound of a CRT tube warming up. Make sure the monitor is plugged into a good outlet by testing the outlet with a lamp or any other device that will prove beyond a doubt that the outlet is good. Make sure that the power cord is either permanently attached at the monitor end or that it is seated fully in the socket, since partial cord insertion is the most common failure for monitors with detachable cords.
LCD displays don't make any sound when you turn them on, but they don't always have a simple power cord, either. Some LCD monitors are powered by an external transformer, which in turn is powered from a regular AC outlet. If the LCD display doesn't show any signs of life, make sure that the cords into and out of the transformer are fully seated. Some transformers are equipped with a status LED to show when they are operating, though you can also check for live output with a DC voltmeter. The power connection to the LCD display is often awkward to inspect, recessed into the back of the display. The important thing is to make sure it is started correctly, then seat it all the way.
Few things related to computers are more embarrassing than taking your monitor for repair and finding out that the brightness was turned all the way down. This frequently happens with exposed dials when you pick up the monitor and move it, though a prankster might also turn down the settings when they're concealed behind a pop-out door right under the screen. Make sure that manual brightness and contrast controls on the monitor are set somewhere in the middle of their range, since it's not always obvious which way is maximum or minimum. If the monitor is alive, turning the brightness and contrast all the way up will often result in the screen lighting up a little. The easiest way to check if the monitor is good is to simply attach it to another working PC.
If you see a message on the screen that includes "power" in it, like: "attach graphics card power", "no power to video adapter", etc, it means that you have a PCI Express or older AGP video card that requires more power than the motherboard can supply through the bus. This means you need to run a power cable directly from the power supply to the video adapter, inside the PC. If it's a new build, you may have forgotten or not seated the connector firmly. If it was a working PC, either the power supply lead has failed, the power supply itself has problems, the cable worked loose, or some hardware on the video card has failed.
Earlier video cards that required additional power from the power supply usually took a Molex connector, the same 4 pin connector used to power non-SATA drives. Newer power supplies include one or two six pin PCI Express supplementary connectors designed for power hungry graphics cards. Some PCI Express cards, in the absence of a six pin supplementary lead, will accept two 4 pin Molex leads.
Most new monitors will display something such as "No signal source," or "Attach video signal," as long as they are healthy, and powered on. These messages should appear even if the PC or video adapter is dead. This is actually one of the more useful innovations in monitor technology, because it offers definitive proof that the monitor or LCD display is alive and most likely capable of displaying an image if a video signal was present. Unfortunately, it only proves something by its presence, since older monitors and cheaper models may not display anything at all.
Make sure the 15 pin video signal cable (3 rows of 5 pins each for SVGA) is seated squarely on the video port on the back of the system. The hold-down screws on either side of the connector should be screwed in all the way, but not made up too tight. If the video cable is connected correctly, remove it and inspect the connector for damage.
Before making yourself nuts, test the monitor on another PC or laptop. If you use a laptop to test the monitor and it doesn't automatically detect an external monitor when booting, use the "F" function keys along the top of the keyboard to tell the laptop to shift to the external display. Remember that we are testing just to see if the monitor is live, it doesn't matter if the screen settings are wrong and the display looks funny. If it doesn't work on a known good computer, the problem is with the monitor, not your PC. If a faint image is detectable on an LCD screen, the problem is with the backlight or the inverter that powers the backlight. A loud buzz coming from an LCD monitor is most likely the inverter circuit failing, though it can go on getting louder for years before it pops.
Look carefully at the pins in the connector to make sure none of them are at an angle or flattened against the bottom. Note that missing pins in a video cable are the norm, usually the monitor ID pins. It's great if you have a spare video cable and a monitor with a detachable cable, but most monitors have an integrated cable (doesn't detach) and most people don't have a spare anyway. You'll usually have to settle for visual inspection for whether the cable may have been crushed or breached.
If you see that a pin in the connector is bent, you can try to straighten it very slowly with tweezers or fine needle nose pliers. If a pin breaks, you can buy a replacement connector and solder it on with a fine soldering iron and infinite patience. You'll also need a heatshrink gun and tubing if you want to do it right. The last time I did one it took me almost three hours, though I didn't really have the right soldering iron tip. I don't recommend making your own DVI connector.
Video Connector Pinout
Doyou hear a string of beeps? Healthy PCs should beep once or twice when they are turned on and pass their Power On Self Test (POST) routine. While different BIOS manufacturers use different beep codes to identify failures, a repeating string of beeps (three or nine in a row) is a common indicator of video card failure.
Check whether or not the video adapter is properly seated. This is an in-the-box check, so make sure you unplug the power cord to the system first. This doesn't apply to motherboards with built-in video. Whether or not the video adapter appears to be seated properly, reseat it. Remove the video adapter hold-down screw, remove the adapter, then reseat it in the slot, pushing down evenly. Be careful that putting the hold-down screw back in doesn't lever the front edge of the video adapter (the end away from the screw) up a fraction of an inch out of the slot, because that's all it takes if there's no hold-down latch.
If reseating the card doesn't clear up the beeps, it's probably a failed video adapter or RAM on the motherboard. You can power down and try reseating the RAM at this point, without going all the way through the motherboard diagnostics. There used to be beep codes for all sorts of component failures, but most of those components have long since been integrated into the motherboard and can't be replaced if they fail.
DoesDoes the system get as far as showing the BIOS screen and locking up? By BIOS screen, we're talking about the text information or brand-name graphics that appear on the screen in the initial boot stages. A system that freezes up at this point is rarely suffering from a video failure, though a conflict between the video card and another installed adapter is still possible.
Did you install any new adapters immediately before the problem appeared? With the power disconnected, remove any other adapters, one at a time, then reconnect power and attempt to reboot after each removal. Locking up on the BIOS screen is often due to an adapter conflict, but if removing the other adapters doesn't solve the problem, proceed to Motherboard, CPU and RAM Failure.
Do you get a live screen, or at least move past the BIOS screen, with all the other adapters removed? If so, the problem is either a bad adapter preventing proper operation of the bus or an adapter conflicting with the video card. In either case, you can reinstall the adapters one at a time, powering up after each one, troubleshooting the problem by process of elimination. Don't forget to unplug the system each time before taking any action inside the case.
If the motherboard is a new upgrade, try the video adapter in another system before trashing it, since it could be a simple incompatibility. If installing a new video adapter doesn't solve your "dead screen" problem, it's probably a motherboard related problem, even though you got to this point without any beep codes. Proceed to Motherboard, CPU and RAM Failure. I just added an illustrated guide for how to replace an AGP video adapter to the site.
Computer Repair with Diagnostic Flowcharts | Power Supply Troubleshooting | Video Card Diagnostics | CPU, RAM Motherboard Troubleshooting | Hard Drive Failure | CD and DVD Troubleshooting | Modem Diagnostics | Sound Card Problem | Network Troubleshooting | Order Book