Lenovo Ideapad 100-15IBD Troubleshooting

[tjk0102]

Hello Everybody. I am currently trying to troubleshoot a Lenovo ideapad motherboard that turns on for a moment and shuts off. The motherboard model is: NM-A681 Rev 1.0. The computer shuts off before the bios splash screen can be reached. After probing around, I found there is a short from the 3.3v (Labeled 3VALW in schematic) to ground. I did inspect the board, there are no signs of liquid damage or corrosion. I also tried injecting 3.3 volts and using alcohol to find hot spots, the only thing that got slightly warm was the cpu. I am still new to troubleshooting motherboards, and I was wondering if anyone had any suggestions or pointers of things I should look for to help find the culprit.

[piernov]

Re: Lenovo Ideapad 100-15IBD Troubleshooting

What is the resistance to ground on the 3VALW line? Measure resistance on the +3VS and +1.05VS lines too.
Make sure you inject voltage without the AC adapter/battery plugged in.
When you say CPU, do you mean the smaller die (which is the PCH) or the larger die (which is the actual CPU) on the CPU package?

[tjk0102]

Re: Lenovo Ideapad 100-15IBD Troubleshooting

Thank you for responding Piernov.
The resistance of the 3VALW line to ground is 22.9 ohms.
The resistance of the 1.05VS line to ground is 188 ohms.
I have injected the voltage without the ac adapter connected.
Also, the smaller die located on the cpu package gets warm. (PCH)

[piernov]

Re: Lenovo Ideapad 100-15IBD Troubleshooting

This indicates a dead PCH, ie. nothing you can do except if you really want to replace the CPU…
Check the resistance to ground on +3VS line anyway.

[tjk0102]

Re: Lenovo Ideapad 100-15IBD Troubleshooting

I just checked the +3VS line, and there is no short. I do have another motherboard the same model in which I tried to inject voltage into 3VALW and the PCH did not get hot. So in short, this confirms the PCH is the issue. For future guests to read this post, if you do a resistance check from test pad PJ303 to ground and have a short, the processor is most likely the culprit. Thank you Piernov for your help, I really appreciate it.

[LM80]

Re: Lenovo Ideapad 100-15IBD Troubleshooting

Hello, I have the same problem ( start for a moment 0.5 s and fan start to run). I check ( inject ) all the tensions - are ok ( small current absorption ~100-150mA) , i don't have short circuit on +1.05vs , +3vs, +3valw. I take down PQ39 ( mos to ground ) and in this way pc start, i hear the hdd but don't have display and the fan is don"t working and on the pin 1 of PL9 is 3.05 volts. Thank you .