Request for some pointers on more depth latptop debugging

FusionHamster · September 8, 2023

Hi, it's my first time here so apologies in advance for anything I may have done wrong.

A few weeks ago I disassembled my laptop (medion erazer p6689) to clean out the heat sink (and to try to disagnose a problem involving it force turning off when it's bent - something it's been doing for ages) - I've done this a load of times before (replacing thermal paste, upgrading ram etc).

After reassembling it, there was no sign of life at all from it. We've tried a lot of things which I'll list below in a bit of an info dump in case any of it is useful.

What steps am I able to take with the motherboard to debug how far it gets into booting before something goes wrong? I've done a lot of googling to see where i might be able to probe to check how far power is getting, wether it's possible to extract the post code somehow from the chip etc, but I think I'm not using the right search terms (or this sort of thing is dumb and not worth the effort)

Information that would be useful (for me) is:

What are some general boot stages, and where might it be getting stuck? Since the harddrives don't make any sounds, no power lights come on and the cpu fan doesn't move, my limited knowledge suggests that it hasn't reached POST. However, i'm not 100% sure. I have very little (if any) knowledge of what happens before POST, so I can't do much theorising.

Which things (in general) can I unplug from a laptop motherboard, and have it still boot? (in the interest of ruling out other boards which may or may not be broken). There's a few daughterboards - one for some USB and audio (which has broken and been replaced before), one for the SD card reader and power LEDs, one for the 2.5inch hdd slot, and one for the disk drive. The screen, touchpad, camera+mic, speakers, both drives, wifi module and keyboard are also removable / separate from the main board as well.

Where might I be able to probe on the motherboard for more information? Things like which ICs may or may not be recieving power, if some signal must always be sent, etc. I have multimeters and occilliscopes.

Info dump:

It's probably not worth anyone's time to read through all of this, but i'm just going to put as much information as I can here in case any of it is useful

Troubleshooting steps:

So far, we've tried replacing the ribbon cable going to the power button (in case the power button just wasn't working)

Running the motherboard on its own (no screen, no hds etc),

Repeated reassembly + disassembly of the laptop

Removing the cmos battery (both to reset the CMOS and also to force it to turn on when it recieves power - something which seems to work on other computers in case the power button was still broken).

shots in the dark about what could be wrong:

I spun the fan while blowing out dust from the heat sink. This may have either blown up some stuff in the fan, or broken the fan controlling circuitry on the motherboard.

I've confirmed that the cpu cooler fan (probably) didn't break while I was cleaning the heatsink by plugging it into 5v while disconnected from the motherboard.

One of the copper traces has separated from the ribbon cable which goes to the screen. I'm 90% sure that this was already a problem, however. The trace in question goes to the board above the screen, which houses the webcam and microphone. Neither of these have been working for ages. However, it could be possible that the broken piece of trace was moved about as i reseated the screen cable, shorting some pins on the connector.

The CMOS battery was plugged in while the PCB was out of the case and I was cleaning it. Maybe I somehow shorted something and broke it? This seems unlikely, but not out of the realm of possibility.

Maybe i've just got really unlucky and ESD bombed it? I'm not sure how to test for this though.

Other than this, i've got no ideas. It's making the debugging process really hard, because as of now I can't extract any information from 'nothing happens'.

Some interesting observations:

If I hold down the power button for ~7 seconds with both the battery and charger plugged in, a red LED on the front daughterboard lights up. I think this LED indicates that the battery is charging, so power is definitely making it's way somewhere. However, the laptop is able to charge whilst completely off, so it doesn't confirm much else.

At some point, we checked the charge of the CMOS battery, and it was dead. I'm not sure why this could be - maybe that happens when the laptop has been unplugged for a while? We replaced it, no luck.

Finally:

It's possible to buy replacement parts for this laptop surprisingly easily. I know where I can get a new motherboard for about £200, but i'd rather not spend that money unless I can confirm that the motherboard is dead and irreparable, since the problem might stem from something else, or I might just be being an idiot and not checking something obvious.

It's also possible that something is wrong with the laptop such that installing the new motherboard will just kill it instantly, which I don't want to run the risk of.

I'm going to this length mostly because I can, but also because this laptop is rugged, performant and super easy to fix (most of the time), since the manufaturer themselves still sell replacement parts, and in todays mess of anti-user repair design I don't think i'll be able to get a new one like it without buying a framework, which isn't really worth it considering i've got a functioning PC.

Thanks for reading!

ItTakes2ToMango · September 8, 2023

34 minutes ago, FusionHamster said:

What steps am I able to take with the motherboard to debug how far it gets into booting before something goes wrong? I've done a lot of googling to see where i might be able to probe to check how far power is getting, wether it's possible to extract the post code somehow from the chip etc, but I think I'm not using the right search terms (or this sort of thing is dumb and not worth the effort)

Hit the nail on the head there.

I've never heard of any way to do what you're asking without advanced tools/electrical engineering knowledge. Maybe someone here knows but

Your problems are reminiscent of a dead CPU or Mobo - Good luck