Dell Inspiron 7560 randomly powering off

[pingaroon]

Hi all,

I have a nice i7 Inspiron 7560 motherboard which appears to be perfect with the exception of the major flaw I will describe.

It just switches itself off after a short period - sometimes very early in the process, even before the Dell logo comes up. The power button brings it back up again, but it switches itself off normally after between 5 seconds and 2 minutes. Sudden power off, no lights. Not heat-related - it never gets the chance to heat up the heatsink.

When I first got it, it would stay on for longer than 2 minutes - anywhere up to 15 minutes, booting ubuntu off an HDD no problem, but then it would switch off and *would not come back on again* for at least one hour! After waiting and waiting, it would then power on again normally and zack! power cut again.

Now it seems to always power on when pressing the power button, but it cuts out so quickly.


How to even begin to find the fault?

Thanks guys!

[mon2]

Re: Dell Inspiron 7560 randomly powering off

1) What are the details of the power adapter? Is it the Dell original? What is the power rating of the adapter ?

2) Check the DCIN connector and measure the voltages @ PJPDC1 while the laptop is working.

When it turns off, check again the voltages of PJPDC1.

Post the readings for both cases.

3) Compare the voltages at each and every coil when the adapter is connected and the logic board is working. After it turns off, check the voltages again of each coil. Each coil will be linked to a local switching power supply.

[reformatt]

Re: Dell Inspiron 7560 randomly powering off

In my experience turn on followed by shutdown is usually due to a missing power rail. Check the board closely under a microscope for corrosion. Had 3 this week with corrosion around various buck converters. It can be quite minimal, most are QFN's with corroded connections or tracks eaten away nearby.

[pingaroon]

Re: Dell Inspiron 7560 randomly powering off

Hi, it's a Dell original 65W with healthy and constant 19v at PJPDC1. It never drops below this even when the laptop turns off. Charger is good on other machines.

When checking the coils (there are 12!), most of them are still outputting their expected voltage even after the machine starts powering off and misbehaving.
The more frequently the re-powering-on after a shutdown, the more quickly the problem presents, and after repeatedly powering back up, I noticed problems with the coil voltages on the cpu and the gpu. When the board is cold, these 4 coils all have 0.8V after a power on. When things go bad, the gpu coil voltages are zero and sometimes the cpu coil voltages. Measuring resistances, when the board is cold, the gpu coils are 30ohms and the cpu coils are 9 and 18 respectively. After things go bad, these resistances drop to 20, 20, 7 and 15. The lower that resistance, the more noticeable the fault. Measuring these resistances every one minute with the board powered off, they start to creep back up to normal. Once they hit 30, 30, 9, 18, the board boots up normally every time. They then quickly start to leak voltage and the problem presents. It won't stay on longer than 2 mins.

I guess my next move will be to check the mosfets around the gpu and work out where the mosfets are for the cpu power supplies...?

Thanks, getting closer..!

[pingaroon]

Re: Dell Inspiron 7560 randomly powering off

In my experience turn on followed by shutdown is usually due to a missing power rail. Check the board closely under a microscope for corrosion. Had 3 this week with corrosion around various buck converters. It can be quite minimal, most are QFN's with corroded connections or tracks eaten away nearby.

Hi, yes good idea to check - the board looks almost new - no signs of any corrosion

[pingaroon]

Re: Dell Inspiron 7560 randomly powering off

Update: the board died - cpu failure