1) 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?

2) Is it usually a bad capacitor?
badcaps seems to think so. What about a bad connection?

3) How do you perform the component level repair?
So you've found the bad capacitor or component, can you really solder a new one on without hurting the components around them? What's a good soldering iron for under $100?

Answers to your questions

Diagnose problem:
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 notbook motherboard:

1. make sure main system powers are ready, that is 3V and 5V.
2. switching circuit is ok, which involes IO/Keyboard controler, south bridge
3. 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 not matter if the cap was burnt or not.
Loose connection
Mostly happen on VGA chips, south birdges and the places close to CPU. Hard to troubleshoot and need lot experiences.

How to repair?
You need specialised tools. I have DC power supply which can display current change and set to different voltage and current output. You need Really nice soldering station, SMD rework station, BGA rework station, etc. I also have more than thousand schematic diagrams, all together about 10GB and you could not find anywhere in the net.

I have seen the video in youTub teach people how to fix VGA problem, and I guess you only have 30% chance if you follow it. My BGA rework station tutorial can perform up to 95% successful rate.
Troubleshooting Dead HP G6000 Motherboard

Things that are likely worth solving:

Bad capacitors. Decently common and the parts only cost a few cents.

Most of the ICs on board... 4-20 pin jobbies such as the power ic do fail and are swappable for less than a buck or so

Blown fuses. Easy to diagnose easy to replace. This is a definite.

Any and all damaged jacks. Power and audio being the most commonly broken.

Resistors. easy to find easy to replace. cost is in pennies

Transistors and diodes can be more problematic to diagnose and fix but they too are cheap and swappable with just a soldering iron.

Obviously you can swap cpus so you should be able to diagnose that as well.

Case Study 1

"Machine: HP G6000(same mainboard as V6000)

Problem: Laptop will not power up, completely dead

Discription: The machine has been water damaged. It does not have system standby power, which are 3V and 5V.

Finding 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 adaptor ok with mainboard).

Everything ok except 10 pin, ACIN is 0V. This is incorrect, mainboard doesn't detect there is an adaptor! 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(the connector of multimedia switch board). Fix it and it start to charging battery. Switch on with power adaptor, ok. Remove the power adaptor once switch on, battery keep the mainboard running, ok. But still can't switch on from battery once remove the power adaptor. Think, think, do I miss something here or there? Oh, the CMOS battery not installed, put the CMOS battery back and everything work perfectly. The battery part of troubleshooting takes me about 3 hours.

Remember, system may not run if you don't have CMOS battery or CMOS battery is low for some AMD cpu mainboard.

Case Study 2

"Machine: Acer 4600

Problem: Laptop will not power up

Discription: The machine wont turn on when customer bring in.

1. plug in our power supply and it shows short circuit on board, the current jump to the 5A, which is the limit of my power supply.

2. take off the mobo, drop the voltge of power supply to 5v, limit current to about 1A, plug in again and find a mos very hot.

3. replace this mos, now the short circuit fixed.

4. turn on, the current goes up to 0.3A and stopped, it should go up to 1A during booting.

5. touch cpu, not hot, no power to cpu.

6. check the cpu pwm, which is max1907a. all conditions to make it work are present, but still no power output. the ref voltege is 0. so most likely this chip gone.

7. I replace the chip and everything work fine.

For lots of unknow brand laptops, sometimes very hard to find drivers. I don't know how many people know there is a trick to install a similar driver.

Machine: TPG (can't see the model clearly)

Could not find the driver, TPG web site only point to Asus web site and doesn't give which model it clone from Asus. We can't find vga driver.

We use Everest to check what vga chip it use and find it is ATI IGP 320M U1. Download few from different web sites, all of them just give a message said could not find hardware it supports.

Finally, download a driver from fujitsu web site for the lifebook S2020(same vga chip and south bridge chip as TPG's). But still give the error message said no support hardware find.

Every device has a Device Instance ID, and windows will compare this ID with driver's INF. It will install the driver if it find a match ID and match SubSys, otherwise will give an error message.

We check the driver for S2020, find the string "PCI\VEN_1002&DEV_4336&SUBSYS_118110CF" in one of the INF file. We also find the Device ID on our machine is "PCI\VEN_1002&DEV_4336&SUBSYS_2029161F&REV_00". Device ID is matched but just into different sub system. Replace the string in S2020's INF with our Device ID string, driver is installed correctly and no error message.

Dell inspiron 6400 with a power problem.

Laptop can't run nor charge the battery on adapter, but on battery it's run.

This is typical protection circuit problem. check the 2 mosfet just after power socket

Charging problem

C700's charging chip is 39A126, DV6000/9000's charging chip is max8724 or max8725. Check the working conditions of those chips. such as VIN, ACIN, ACOK, LDO, REF, SHDN.

Charging problem is second hardest problem on notebook repairing, the first one is signal level everything looks ok but just no display.

usb no power

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(becareful, 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).

Dark image on the screen , just very hard to see, a torch will show it is there though).

When we fix such problem, usually we do the following:

1. find an known good lamp or screen, plug into inverter see if its light up. if it lights up so you need to change your screen's lump.

2. if it not light up, do following:

a. check power(either 5V or 19V), enable signal(3V), brightness control(3V) are presented. (all testing by done with adaptor plug in).

b. if all those presented, then change inverter otherwise

c. need to find out which wire is power, which is enable, which is brightness people find hard in here because they don't know how to find out which is which.

Power always connect to fuse (also need to check fuse is ok). for the other two, you need to check inverter pwm's datasheet to make decision. Just start from pwm's EN and Brightness pin, trace back to connector. After you find out, make sure all these wires has normal resistance to ground, otherwise you have to cut off the wire that abnormal. Then try to find exact voltage from mobo and connect to inverter, by doing this you are not really fix the problem but bypass it. It is a easy to work around it rather than fix problem.

Q. The first step to troubleshooting is monitor the current change. usually, current reading can tell what was wrong and quite accurate. You frequently mention monitoring the current change to pinpoint the area of failure. Can you please describe this troubleshooting technique in more detail with some guidelines and numbers to look for?

A. To understand why current changing, you may need to know the basic powering states of notebook which is called ACPI standard S0 to S5.

S0 is full runing state, S5 is state that after you swith off laptop but with either power or battery presented. out off topic here, the S5 is the state after you shut down computer not the state you just plug in the power. Power button is for wake up computer from S5 and enter into S3. In ACPI standard, to switch on computers you need a signal "RSMRST". It explains why some laptops auto switch on if there is no CMOS battery, because its EC send RSMRST when power plug in. But you need push power button to switch on laptop if there is CMOS battery, because laptop remembers it is in S5 state.

Powering up a laptop can be divided into few parts, first check south bridge's gpio defination, check communcation between bios and south bridge, check system ram, power cpu, power up vga. so you can see the current goes up and down. step by step it reaches to full power.

Current changing monitor is just give you rough idea, sometimes not so accurate. let's see 2 examples:

1. a hp 530, power up but stay on 0.68A. it should go down a bit after 0.68A, and up again. The faulty mobo current change is 0.02 - 0.3 -0.68. After we see this current, we know it may have problem on SB or may be on NB but most likely is SB.

I check LPC 0 to LPC 3, no signal find. it may have problem on SB or BIOS. So I flash the BIOS before I do anything on SB. It was fixed after I reflash BIOS.

2. DV9000. Normal mobo: 0.01 - 0.3 -0.9 - 1.1 - 0.9 - 1.2 -1.45 then display. we find faulty mobo 0.01-0.3-0.9-1.1-0.9, by checking DMI Link we find there is one or two pulses. So we have an idea that it already pass memory checking, the next stage is VGA checking and active VGA output. In here, if it stop in 1.1 it most likely NB or SB problem, but if it stop in 0.9 or after, it may be the problem of VGA.

Current changing gives you an idea about where is the fault but not 100% accurate. People ask me what fault by just give me the current reading and I always say you need to give me the changing states, how many jumps that current made.

Machine will run on charger with battery removed instal the battery and it will only run on the battery not the charger

Looks like discharging has problem. When discharging mosfet has problem, or the Gate voltage not correct, the 18V of main power will directly go to battery.

The current will be very large when you have short discharging mosfet, if you plug charger in and have battery installed at sametime. Laptop will detect this abnormal current and refuse to start up. Remove either one, machine can start up.

How to 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 singal. read the current change during booting tells you where the machine stopped. check the singals on the different part of motherboard tells what is wrong or what is missing.

Tools are: smd rework station, bga rework station, power supply has 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 mainboards? 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.

For details: Please visit our techblog below

http://www.laptoprepairtrainingcollege.com/techqblog.html

 

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