How to figure out whether GPU, CPU or motherboard is broken?

Question

So I was "hacking" my internal laptop monitor (basically I was trying to understand the pinout and try to use it externally). During that I used continuity checker to trace circuitry. It is my old laptop so it was meant for experiments.

Now I did something and I don't know what I did. Neither internal nor external monitor is working. I am afraid that by using continuity tool I have damaged some sensitive components.

Is there a way to check approximately where the issue is - gpu, cpu or systemboard?

I know the following points may mean nothing, but maybe they will be usefull:

• GPU and CPU heat up
• Motherboard supplies power to VGA and internal monitor sockets (including inverter)
• I am testing without all unnecessary peripherals (just ram, motherboard(&its intergreted components), cpu, gpu). It should show blinking bar. Not monitor is not even started(stays on sleep mode)
• Monitors have been checked
• I have oscilloscope, external power supply - if checking testpins is the case, I could do it.
• I cannot replace cpu or gpu - buying spare parts and checking wouldn't be the best idea.

Please ask any additional information you require. I will try to answer.

Answer 1

You might have messed up some of the soldering by poking at it and messing with the traces.

This is actually a common issue though with solder needing to be re-flowed and the graphics not displaying due to that. If you see the hard drive activity light going it means probably just the GPU connections maybe messed up. It is possible that you that you gave it some build up charge when touching it (electrostatic discharge - ESD - as mentioned in the other comment) and fried something that wasn't suppose to have that much current/voltage going through it.

Here are some guilds on re-flowing the solder however as it seems in your situation its worth a try. You'll want to completely disconnect the motherboard from the laptop which might be difficult depending on your laptop. No plastic exterior stuff as it can release toxic fumes when heated. You then want to heat it to the temperature which solder "flows". This is going to take a few hours between getting the motherboard out then heating it, although you don't want to heat it for too long. Make sure it is just the motherboard and cpu/gpu in there.

I wouldn't put the hard drive in there as you don't want to heat up the hard drive as that can cause issues/premature failure. All the other solid state stuff should be fine as long as you have it at that temperature for not too long, 10 minutes in the oven should be good. At some point you can cause damage to the solid state components.

You can do it with a heat gun as this person did:

• "GUIDE: Reflow GPU fix"

Or in an oven as these people did:

• "Holy crap, it worked! Dead video card resurrected!" (this is probably the best reference)
• "How to Reflow a Laptop Motherboard"

Testimonial from someone who has tried it here on superuser:

• Graphics card failure, anything I could try

This is about all I could think of as a solution. Its either this or something else like ESD or possibly scraping off a surface mount component on the board when you were poking around... or some other very unlikely reparable damage.

I know I personally scrapped of a really small ceramic capacitor on a (at the time) $300 video card and I couldn't figure out where it came from. That or I couldn't get it to solder it on to the spot I thought it came from correctly since it was so small. Either way I had to chuck the whole thing.

Good luck. Let me know if this helps.

Answer 2

My guess is that somehow you applied some current or static electricity to a component which wasn't supposed to be touched. I've read that it only takes trivially small voltage to fry a component, sometimes as low as 5V, sometimes around 100V. In comparison, the static electricity spark that you can feel is somewhere on the order of 20K to 25K volts.

Good luck.