Laptop Motherboard Diagnosis/Repair (No Power)

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).

Ambiwlans

Posted 2010-10-22T22:27:12.510

Reputation: 383

2I'm not familiar with this kind of work on the level you're doing it, here, but I can tell you schematics for proprietary laptop motherboards are going to be hell to come by. I don't know of anybody who seriously does the sort of stuff you're talking about in the interest of laptop repair. Even if it WAS something like a burnt northbridge that you can localize and (potentially) replace...nobody does that. You just purchase a working replacement motherboard. – Shinrai – 2010-10-22T22:57:39.697

It IS done. But generally they have a rework + reflow station afaik. Buuuuut the guy before me apparently had a >80% success rate with the same tools I have. He left for a different job and I'm stepping into this freak's giant shoes. Which makes it a bit daunting. When there were no laptops to repair he fixed random dead components left in the shop... like sticks of ram or inverter boards. I wouldn't be shocked if the dude made his own resistors from bits of scrap he found in the shop. – Ambiwlans – 2010-10-22T23:56:10.807

Answers

In order to boot there will already be current flowing through the li ion charging circuit and such. Have you tried testing various spots on the motherboard and then trace along the dc input jack and fanning outward for any sign of power?

The boot method is basically a complex relay so there is bound to be power somewhere. If not then you may have to start checking out the regulators and each individual component. Probably cheaper to replace the mainboard than spending the time to isolate individual defective components, source parts and then finally repair, especially if you don't have any type of schematics or much experience.

To not even get into post, best case scenario is an unsteady or erroneous voltage from the power supply section due to failed passive components. Worst case scenario, everything else..

sauceboat

Posted 2010-10-22T22:27:12.510

Reputation: 176

As far as I know and from my own repair experience it is very rare that you can revive dead mobo if some component on it failed. even if you detect it you most likely won't be able to re-solder it (especially if it is IC), you would just damage it, keep n mind - they are multi layer mobo's, you can overheat the component or neighbor ones etc.

If the component is just 2 prongs and it is pretty big - it is possible.

Here is my experiences, maybe helpful to you:

I had one laptop (TOSHIBA) where the Zenner Diode failed between battery charger and mobo power, so it had your kinda symptoms, i.e. it seemed dead. I traced voltages from power supply and found that after Zenner everything was 0.

Another dead laptop (SONY VIAO) - bios PROM fried - noting works without it, it is like it's been totaled. However, here I knew it was PROM - it died during bios flush. You can by bios pre-programmed for you laptop - there are these guys on e-bay. Not always works but worth a shot if you know it is bios.

The last resort - replace mobo. you can buy them relatively cheap, at least cheaper than new laptop.

Boris G

Posted 2010-10-22T22:27:12.510

Reputation: 119