Modern laptops are complex devices and Motherboard failures are a common occurrence. Many motherboard problems are fixable, despite what some repair shops might say.
"A unique approach to troubleshooting Laptop hardware problems. creates a expert system for diagnosing component failure and identifying conflicts. The diagnostic steps at the core of this book are intended for all Laptop technicians More
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Problem: How do you diagnose motherboards on a component level. What tools needed?
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.
Tools are: smd rework station, bga rework station, power supply with current meter. all the rest tools you can find in any radio tv repair shop. of course all the datasheets for the components, especially the schematic diagram, you will find it much difficult without it.
What are common faults on motherboards? Do certain components fail? Is there a trend as to which parts fail quite often?
Different maker/model has different common fault. Toshiba S1 is vga chip, and can't be repaired(well, almost can't be repaired because the pcb quality is not very good so successful rate is very low). HP DV2000, 6000, 9000, Compaq v3000, v6000, dell 1210, all those use nvidia chips have problem on vga chip or north bridge. easy to repair but have to make fan keep spinning after repaired, otherwise will break down in 1 or 2 week again.
hp nx5000, cpu pwm chip dry joint. acer 290, cpu pwm dry joint. hp dv1000, Compaq m2000 protection circuit easy to blow up. ibm t40 vga dry joint problem. These are just few of them. every machine has its own common fault. but dry joint is the common problem for all machines. Motherboard repair is not as difficult as people thought, i think much easier than repair a tv.
Problem: How to replace the graphics card on a dell 1420, the gfx card is a nvidia 8400gs
Solution: To fix such machine, first you have to do bga reworking on the chip, then connect fan to usb power to make it spin faster and non stop. also need to cut off fan controling wire.
USB power problem
Solution: The following solution only apply that usb no power, if the usb device get power but can't be detected or can't be recognised by system, that indicates south bridge problem.
To get power for usb is very simple. use multimeter to find out which usb pin is ground, the pin on the other side will be the power. for example say pin 4 is ground so pin 1 will be the power.
connect power pin to 5v you can find on motherboard, usually a big inductor(be careful, when you measure the voltage, put battery in as well, some mobo the inductor for charging circut give you 5v if you don't put battery in but jump to battery voltage once you put in the battery, such high voltage will burn your usb devices). connect it on the different side of inductor that mosfet connect to(or should I say power out side?) so you can get smooth waveform, don't connect to the same side of mosfet(this is power in side).
Problem: Dell inspiron 6400 with a power problem. Laptop can't run nor charge the battery on adapter, but on battery it's run.
Solution: This is typical protection circuit problem. check the 2 mosfet just after power socket