Laptop Motherboard Diagnosis/Repair (No Power)

[Idiomatic]

I recently got a job (1.5weeks in) as a 'laptop/component repair tech' in a small shop and I'm in over my head. I've replaced/re-soldered AC/audio jacks before and can strip down a laptop to diagnose components but not much beyond that (did one solder reflow in my oven). The tools they had there were an old school multimeter, solder, iron. I brought a desolder pump, capacitance meter, copper braid.

Last two machines (both Toshiba satellites weirdly) I got were like this:

No power, no lights. Stripped down didn't help. Adaptor OK, AC jack OK, Fuses were all ok. Visual inspection gives me nothing (Burned northbridge or some such would be noticeable)

From there where do I go? I guessed it needed a reflow since I didn't have any other brilliant ideas. I haven't been able to find schematics for many boards either which would help (I could check the power IC possibly?).

If anyone here is familiar with this type of work I'd really appreciate talking you for as much as you'll have me. I like the work and I am learning a lot but I'm probably going to lose my job soon, and I'm not sure what resources I can learn from (other techs there can't even solder... had no idea what a de-solder pump was). If anyone has any bright ideas about online resources I'd appreciate that too (troubleshooting laptops lead me here more often than not). Also wondering what cheap tools you might suggest I add to my line... obviously not a rework/reflow station or anything.... I am only getting minimum wage and prefer eating to not

 

[buzznut]

Ok, here's the deal-laptops are not made to be worked on. Desktops are pretty easy to work on and have few integrated parts, unless you're talking about budget models and dell, gateway, etc. Laptops on the other hand are highly integrated, so if there's a failure its likely that the whole mobo needs replacement.

I would invest in a pc repair kit, they sell them on newegg for 20-40 bucks, depending on what you need and/or willing to invest. They are great, and typically have everything you will need.

If a laptop is out of warranty, then the user is likely out of luck. There's a couple things to check as you surmised; the power cord/powerbrick, the adapter jack, and power button. If all those things check out, it is likely a motherboard. Replacing motherboards in laptops is very expensive, at this point it is best to tell the client that you can retrieve the hard drive or the data itself but they need to get a new laptop.

Not good news for anyone. However if it is still within warranty, manufacturers are pretty good about replacing motherboards. I had one die on my Compaq and they had it shipped back to me fairly quickly, and it was the motherboard as I surmised.

The reason for failure can vary, but many laptops die because of heat generated by the cpu or video chip. If a client needs to replace a laptop, I would advise them to invest in a laptop cooler to avoid that issue in the future.

You are going to waste a great deal of time trying to troubleshoot to the component level. Nobody does this, if you can't replace a switch or card to fix this, then there isn't much you can (or should) do. Once you have eliminated all possibilities, don't be afraid to say its a motherboard failure and move on. Believe me, if you are only getting minimum wage for PC repair the folks paying you are not expecting much. Just learn to troubleshoot things quickly and everyone involved will be happy, people don't expect their PC to be in the shop for a week or two.

I recommend you pick up a simple computer repair book and read up. Also web sites like toms provide invaluable insight and advice. Good luck.

 

[Idiomatic]

I can diagnose most any pc problems down to the component level.... thats really easy.

And without a SMD or BGA rework station I likely cannot fix a ton of issues since northbridge problems are fairly common.

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 i can swap cpus so I should be able to diagnose that as well.

I can't fix:
Northbridge or the vga chip without a BGA rework station so that is out of the question even if i have to be able to diagnose it


I found an example of the dude that does pretty much what is expected of me:


"Machine: HP G6000(same mainboard as V6000)
Problem: not power up

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

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. This is the fault that I never dealt with before.

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.

I wrote this just help people who interest in repair mainboard have idea how to check the problems on mainboard."
Source: http/forums.whirlpool.net.au/archive/1223566