Failure analysis of video card auxiliary circuit short-circuit cause

Failure phenomenon: One day the author is home on the internet, the host suddenly power off, but there is no power failure at home, no matter how the switch computer is no response.

Fault handling: The first to think of the power supply, because this power has also been repaired before, is the power supply and bad? The power supply to another computer, incredibly can start normally. And the other computer's power into this problem computer, still can not start. Is it a motherboard problem? The author hurriedly with the motherboard to find businesses, can be tested in the business there all normal, can return to the home again connected to the power or open machine, so I only keep the CPU memory and video card composition of the smallest system, the problem is still, fans are motionless. Urgent, the video card also pull down, try again, this time unexpectedly started! can be loaded back to the video card and no response. is the video card burned? The author's graphics card has a 6-pin power supply interface, each test will be connected to the power supply, simply do not pick up the test once, unexpectedly started, and also passed the self-test into the desktop. After repeated tests found that, as long as the connection to the power supply, the computer can not start.

Fault analysis: The author suspected that the auxiliary power supply circuit of the video card has short circuit. But there is no multimeter on hand and no second graphics card, in order to verify this inference, the author used small bulbs, batteries and wire self-made a simple test tool, sequentially connected to the 6-pin power supply interface of any 2-pin, if the auxiliary power supply circuit has a short circuit, small bulbs will be lit. Test with the arrangement combination method, in addition to an empty needle position, any 2-pin connection can light the light bulb. Corresponds to the power supply, that is, when the 6-pin power supply port, the power supply yellow +12v line and black ground wire directly connected, power supply is shorted, of course, can not open the machine. The cause of the failure was finally found.

Learn a trick: The output of short-circuit, the comparator chip in the power supply will detect changes in the current, and through the drive transformer, PWM switch off the output to protect the power supply and other equipment. The protection circuit of the power supply is often omitted, in case of this situation, not only the power supply directly burned, other accessories will also be difficult to escape a robbery!