T430 laptop doesn't power on- please help me troubleshoot w/multimeter (fixing for fun)

[max_smart]

Hi all,

First off, this forum really helped me out by advising me to cut some ribbon connectors to the LCD panel in order to fix a 70" TV (lots of threads on Sharp TVs with this issue). I didn't believe that it could work, but it did.

Now I've been encouraged to try to diagnose something quite a bit more complicated. That is an old T430 motherboard. I work on a college campus so I have access to pretty decent tools. I found the schematic for the motherboard on the site, and have been following traces and taking DC measurements from things. I also don't mind if I break it. Also, there's every possibility that I have broken it by messing around with the multimeter.

https://www.badcaps.net/filedata/fetch?id=1991287

Anyway, the backstory is that a colleague was borrowing the laptop when it suddenly started to make "a horrible mechanical sound" and then stopped. Pushing the power button would not turn it on-- well it would flash for a second, the CPU fan would make a noise for a fraction of a second, and then it would turn off.

I thought since it made a sound it could have been a mechanical hard drive failure, but on opening, it was an ssd. So, I think the only other thing "a loud mechanical sound" could have been was the CPU fan (or the dvd drive which I have removed, to no avail.) If it was the CPU shorting and overheating, and the fan whirring up, then dying, that would make sense.

I inspected the circuit board by eye and didn't notice anything out of place.

I looked for large chunky inductors to both measure resistance to ground (to detect a short) and when it was on, see if they were carrying a DC voltage relative to ground. I also tried some signal tracing and MOSFET testing.

I think where I am stuck is on page 78 of the schematic. There's VINT20 going in at 18V (measured with multimeter), and it seems this chip makes a 5V and 3.3V output going through inductors L3 and L4 to supply other parts of the circuit board. I don't know whether this chip is bad, or some other part of the motherboard is sending it a signal NOT to power things. Any advice would be appreciated.

Thank you.

[max_smart]

Oh, here's page 78 too.

[mon2]

Hi. Are both of these rails off? Measure the voltage to ground of the enable pins EN1 and EN2. These enables are used to enable the rails.

With no power, measure the resistance to ground of each inductor to be confirm there is no short. Post the resistance in ohms.

[max_smart]

Hi mon2, thank you for replying. Both the 5V and 3.3V measure at 0V when power is applied. EN1 and EN2 both trace back to a single M1_ON coming from the ThinkEngine chip. I will test EN1 and EN2 when I get to work next. I did write down those resistances (ohms):

L3 0L
L4 265
L5 0L
L1 6.4
L2 4.2
L7 180
L35 22
L6 275

also found this: https://logi.wiki/index.php/Resistan...ist#Ivy_Bridge

[JMCat]

max_smart Thanks for the info on the Sharp TV. I have a Lenovo T430 and 430s. I belive they both share a similar build.

[max_smart]

Hi JMCat, sure, no problem. This forum is great-- but I did read ALL the information before daring to cut any permanently-bonded-to-lcd cables.

Ok, I probed EN1 and EN2 while turning on the machine. They both start at 3V for about a second or less, then turned off (0V). I also probed L3 and L4 while turning on the machine, and those rails never came up from 0V.

[projekan aja]

i have same problem, is there any update ?

[max_smart]

Hi projekan,

I don't think there's any update. I also can't say whether your laptop has the same problem as mine without taking the measurements and following some of the beginning steps in the sticky threads.