A compatibles, its configuration is: P4 1.8 GHz CPU ibm lenovo thinkpad t61 6378 laptop cpu cooling fan, gainward GeForce3 Ti 200 graphics, off-brand 845 d motherboard, Hynix 256 MB DDR memory, Seagate 80 gb hard drive, samsung 17 inches flat sc-reens, etc, the operating system is using Chinese Win98 SE. Just started to use few months computer work or very normal, but by the end of November last year one day, computer boot suddenly puzzling crashed, restart after all still calculate normal, just run a few more consumption system resources of the program, more likely to crash turned out to be much bigger. But the author in addition to typing, surf the Internet, but for other application requirement is not much, so also do use. But from the start in January this year, the computer appeared a kind of "strange disease," every time when powered up all need in the over power button, then according to the Reset button to restart to work properly.
 
Breakdown maintenance
 
According to the general system halted fault inspection train of thought, in the ibm lenovo thinkpad t61 6379 laptop cpu cooling fan spirit of "first after soft hard" principle, the author first the heavy Win98 SE, but failed to solve the problem. Then trial assembly Win2000 and WinXP, although the installation process are all very well, but failure phenomenon but remain as before, and on the basis of the author decision this fault should be independent system software. Then replaced a Great Wall 300 w new power, but still did not eliminate the fault. Upon confirmation of hard disk no bad way, the author and in turn replaced memory and graphics, when using a piece of small sized photograph of the GeForce2 MX440 graphics to replace the original graphics, fault finally disappeared.
 
The author thought it comes out of the question, the GeForce3 Ti 200 video card inserted in the other a normal computer ibm lenovo thinkpad t61 6457 laptop cpu cooling fan test, but do not have any problem! At this time the author began to suspect that may be motherboard have a problem. But after careful analysis and think there seems to be no reason, just assembled it worked quite normal! Don't is its AGP slot have bad contact problems? But after replacement display card is running well! Looking at two pieces of graphics, the author abrupt fantasy, is due to GeForce3 Ti 200 video card consumption power is larger, the motherboard AGP slot power supply shortage, or for AGP slot power supply circuit element potential issues, resulting in graphics in the working voltage of the lowest near the critical point?
 
To test the idea, the author will motherboard down from ibm lenovo thinkpad t61 6460 laptop cpu cooling fan the case out, in the light of the strong under the environment of careful observation AGP slot surrounding components, found that there are two with small aluminum radiator and on the mainboard dimension for SD12, SD13 power device, it is estimated that they should be for AGP display card power components, but the appearance observation has not found to have obvious abnormal phenomena. So the author and gainward GeForce3 Ti 200 graphics put back to the main board, and restore all the hardware connection. Then in the computer successful start, the digital thermometer probe were inserted in the motherboard AGP slot power supply for the two dc switch power tube aluminum heat sink in.
 
 
 
And then run the easy to crash the game program, at the beginning of their temperature display digital as 25 ℃ or so, only for about 10 minutes time, the temperature at the same time reached 52 ℃, SD13 temperature numerical suddenly slumps, meanwhile computer crashed. The author overjoyed, immediately cut off the power supply of main computer, and then remove the SD13 of fin and solder iron welding the element, using a multimeter to electric stop check each electrode on-off resistance,ibm lenovo thinkpad t61 6466 laptop cpu cooling fan but did not see any unusual. Look at the cell surface, dimension model for FP45N30T, because the author hand not model the same power tube, so they use a package volume roughly the same silicon NPN power transistor do replace test, the results of computer start returned to normal, and then run some larger program no longer appear crash phenomenon. Even if the computer continuous operation for a long time, two dc switch power tube fin highest temperature also only up to 30 ℃ or so.
 
summary
 
Afterwards the author analysis, cause the system halted the main cause of fault, is the main board for AGP slot power supply two power tube in a because exist some defects, which supply in large current occurs when the interelectrode cut-off condition. We can see the author draw out of the circuit diagram, from the graph, we can see that, this circuit is a kind of typical "energy saving control" type double tube parallel power output form ibm lenovo thinkpad t61 6480 laptop cpu cooling fan. When AGP CARDS power consumption is low, the control chip will SD13 tube is responsible for all this power output closed, so as to achieve the purpose of saving energy. And when the graphics card electric power consumption, the control chip will automatically open we should power output.
 
SD13 tube for some reason the performance parameters changed, in the computer just boot AGP slot power supply should be the SD12, SD13 two pipe share responsibility, but in fact but now SD12 to bear, causing the output current in graphics minimum working current point of critical point. As we all know, high power dissipation of the start of the current video card need is very big, so the computer will appear one-time start failure problem. Choose after restart, because in the last card under the impact of starting current,ibm lenovo thinkpad t61 6481 laptop cpu cooling fan power consumption reduced, so start can be successful. But the power supply capacity also is only scrape by, so when graphics high-speed work will appear the phenomenon of crash. And GeForce2 MX440 graphics power consumption relative to lower, at this time due to the energy saving control circuit has been closed the SD13 power supply circuit, natural computer can work properly.