!!! Find Solution to Your Laptop Motherboard Problems !!! Component Level Motherboard Repair (Not Replacement)Problem:How do you diagnose motherboards on a component level. Solution: I find it is very hard to explain this. actually, it is very simple and can be described in two words: current and signal. read the current change during booting tells you where the machine stopped. check the signals on the different part of motherboard tells what is wrong or what may be missing.Problem: How do you diagnose the exact component failure?Obviously, a burn mark is a dead give away, but what if there are no visual signs? Do you poke around with a multi-meter?With what voltage settings and how do you know what to look for?Is it usually a bad capacitor?What about a bad connection?How do you perform the component level repair?Solution: [Answer to all your above questions]This is the hardest part in notebook repair. Basically, we measure voltages on motherboard and there are few power supply range from 1V to 12V on the motherboard. For example, north bridge needs 1.05V, 1.2V, 1.5V, 1.8V, 2.5V, depends on model of north bridge.We also measure all sort of signals, such as PCIRST, CPURST, CLK. We measure the resistances of each AD line from north bridge to CPU/RAM.We watch the current changing patterns to get rough idea where is the problem.There are some simple steps to follow when checking a notebook motherboard:1. make sure main system powers are ready, that is 3V and 5V.2. switching circuit is ok, which involves IO/Keyboard controller, south bridge3. power sequence is ok, which you can see the current jump up and down for few times.4. all the necessary signals are not missing.About Bad Cap:It happens but only about 10% in those motherboards need to repair, and it is the easiest fault to repair no matter if the cap was burnt or not.Loose connection:Mostly happen on VGA chips, south bridges and the places close to CPU. Hard to troubleshoot and need lot of experiences.Tools are: smd rework station, bga rework station, power supply with current meter.All the datasheets for the components, especially the schematic diagram, you will find it much difficult without it.Case Study"Machine: HP G6000Problem: Laptop will not power up, completely deadFinding The Fault:Check Max8724(the battery charging chip) first, because to make system has standby power this chip must work correctly. This is a 28 pin chip, we only need to test 1, 2, 4, 8, 10, 11 pin. They are VIN(main power for chip), LDO(provide 3.3V for chip itself in order to set REF voltage, also provide signal to drive 2 MOS to charge battery), REF(set reference voltage of the chip), SHDN#(enable/disable chip, a switch), ACIN(indicate the power supply has plugged in), ACOK#(power adapter ok with mainboard).Everything ok except 10 pin, ACIN is 0V. This is incorrect, mainboard doesn’t detect there is an adapter! Trace it backward and find it is very simple – mainboard use 2 resistors to pull the input voltage(19V, directly from dc socket) down to about 4V, so test the first resistor and find it opened. Change it and 3V/5V power come up and mainboard be able to switch on.Then the trouble start when I try to charge the battery. The charging current never go beyond 0.15A and after 10 seconds the charging light start to flashing. Also can’t switch on from battery. First, change Max8724, still same problem. Next check all the resistors around max8724 and change it if it has any sign of watering, still no good. Then change KB3926(EC/KBC, chip monitors the statue of battery), still same.Decide to check MBDATA and MBCLCK, 2 signals that send battery information from battery to KB3926 before I give up. I find the MBDATA is short!Finally, find there are 2 pins stick together on CN10,Fix it and it start to charge battery Switch on with power adapter, ok. Remove the power adapter once switch on, put the CMOS battery back and everything work perfectly.
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