Dell Latitude E7440 FAN issue

[Shummi]

Hi
My own laptop Dell Latitude E7440 have a FAN issue, but i can't figure out what it is, so I am hopeing for a little assistance. I have only repaired one PC so far.....

Suddently the PC shut down, it was due to overheating, as the FAN didnt' run.
What i have tried
1. replaced the FAN, no change.
2. Removed the back-up, reset BIOS, no change
3. Measured the 5V for FAN, always there.

Sporadically the FAN runs when I force power down, so I suspect some kind of SW issue. but I have no idear where to look.

Any help apriciated.

[Adenitz]

Re: Dell Latitude E7440 FAN issue

Hello Shummi,

FAN is controlled by SIO chip. On its connector you have GND and +5VDC and there are two more signals:
FAN1_PWM - control voltage produced by the SIO and the speed of the FAN is directly proportional to this voltage
FAN1_TACH - this voltage is feedback information about the actual speed of the fan.
Did you try with another fan? It is possible that its feedback information is faulty and therefore control signal is not generated.

It could also be possible that something is wrong with the SIO chip and that is much harder to replace.

[Shummi]

Re: Dell Latitude E7440 FAN issue

Hi Adenitz
Thanks for you reply.
These signals are not DC, when the FAN spins theres pulses on both, when it dosn't work
PWM is stady LOW
TACH is stady high
They are comming directly from SIO, but is there another reasons for not starting the FAN?
I think normally the FAN always run at power up, but on this laptop it dosn't

[Adenitz]

Re: Dell Latitude E7440 FAN issue

Hi Adenitz
Thanks for you reply.
These signals are not DC, when the FAN spins theres pulses on both, when it dosn't work
PWM is stady LOW
TACH is stady high
They are comming directly from SIO, but is there another reasons for not starting the FAN?
I think normally the FAN always run at power up, but on this laptop it dosn't

Hello Shummi,

these signals are DC even though not constant. PWM is Pulse Width Modulation. It represents series of pulses typical frequency of about 10 kHz, so the multimeter should measure some average DC voltage. If I'm not mistaken, the pulses go from 0V to 3.3 V.

Just for test, you can try to connect 3V to the FAN_PWM input to test if the fan works and produces feedback voltage on TACH.

The fan should start spinning immediately after laptop is turned ON on DELL 7440.

I had an issue with one HP laptop, the bearing of the FAN was bad and sometimes FAN wouldn't start, I had to provide a little help to start to spin.
So the solution was to replace the fan. It was that simple.

You need to rule out the possibility that the fan is faulty first.

[Shummi]

Re: Dell Latitude E7440 FAN issue

hi Adenitz

Thanks for quick reply
I It is a brand new FAN, and I have also testede it.
I have cut PWM signal, then the FAN runs at full speed.
In case it was the pull up resistor, I have supplied 3.3V throug a 10K resistor to PWM Pin, and it is still LOW, so it IS SIO that pulls it down.
The funny this is, that sometimes the FAN run when I power down.

[mon2]

Re: Dell Latitude E7440 FAN issue

Run the diagnostics to confirm that the thermal sensors are working.

https://www.dell.com/support/kbdoc/e...e-on-a-dell-pc

[Adenitz]

Re: Dell Latitude E7440 FAN issue

PWM Pin, and it is still LOW, so it IS SIO that pulls it down.
The funny this is, that sometimes the FAN run when I power down.

So this control voltage is generated by the SIO. The question is why, is it something wrong with the SIO, or some thermal sensors are out of the range or have intermittent problem, so SIO controls the fan in such way.

Sorin has recently struggled with similar issue:
https://www.youtube.com/watch?v=3Zube6vE5FQ

[Shummi]

Re: Dell Latitude E7440 FAN issue

update: It is not a FAN issue.
The FAN dosn't start at power-on, only when it gets hot.
The problem was intermittent power off.
I have completely disassambled the laptop, and run severalt test, but i coudn't get it to turn off, I suspect the LCD connector, as the diaplay flickered sometime.
Hopefully it will work now, it is currently testing.....
If you hold Fn at pwr up, it goes into testmode in bios (ePSA)

[Adenitz]

Re: Dell Latitude E7440 FAN issue

update: It is not a FAN issue.
The FAN dosn't start at power-on, only when it gets hot.
The problem was intermittent power off.
I have completely disassambled the laptop, and run severalt test, but i coudn't get it to turn off, I suspect the LCD connector, as the diaplay flickered sometime.
Hopefully it will work now, it is currently testing.....
If you hold Fn at pwr up, it goes into testmode in bios (ePSA)

Can you please make this more clear? What is intermittent power off and what you cannot turn off?

[Shummi]

Re: Dell Latitude E7440 FAN issue

Hi Adenitz

What I ment was , the laptop Power-off peridically by it self.
And it still does. Sometime I can use it for a day without problems, then suddenty it is dead, but I can start it again right a way. It is very strange.
I have talked with Dell support, but they just told me to buy a new mainboard.

I am lost, I dont know any tools than can get me closer to the issue, I dont get anything from the Windows log other than "it shut down unexpectedly".

[Adenitz]

Re: Dell Latitude E7440 FAN issue

Well, If I were you, I would use +3.3V_RUN and connect it to the FAN jut to test.
Your FAN has 4 wire (RED 5V, Black GND, Yellow is feedback voltage - RPM, and Blue is control PWM signal).
I would cut red wire from and connect it to +3.3V_RUN to test if the fan is spinning. This 3.3V should go to FAN only and not on the motherboard.

Something like Sorin did here:
https://www.youtube.com/watch?v=ocTOD0vBFgc

If that doesn't work, try to connect it to blue wire also, but only to FAN and be careful no to touch pad on the motherboard. I would cut wires and left connector in the slot intact. This new voltage 3.3V should come only to the FAN.
I don't think you have anything to lose.

[reformatt]

Re: Dell Latitude E7440 FAN issue

Most modern laptops will only engage the fan as needed when temperature requires it. It's a power saving measure. That said, I have seen replacement fans provided with PWM and tach wires swapped so you should always check that replacements match the original in every respect. Sorin has his merits, but he sure does some dodgy stuff. Take what you learn from him with caution.

As it's a shutdown issue, you have to ascertain whether it's a thermally induced shutdown (unlikely, as a Dell will usually throttle the CPU well before that), or a hardware issue with a rail disappearing.

Use Core Temp to check CPU temperature and power output. As it's an Intel system, you can use the Intel Extreme Tuning Utility to indicate what flags are being sent to the CPU etc (like PROCHOT). Prime95 can be used to stress the system, CPU temps should not exceed 90 degress under full load. If it shuts down on full load, but temp is ok, then you have to look at the power subsystems on the board. A physical examination can sometime reap dividends.

[Shummi]

Re: Dell Latitude E7440 FAN issue

Hi reformatt
Thanks.
It is NOT a termal issue. I was tricked with the FAN didnt start at boot.
If i twist the laptop i can sometime get the screen flicker, and sometime just cut off, even if i run it in BIOS test ePSA (hold Fn and PRW ON) So I would rule out HD etc.
When I had it Dissasambled, I couldt get it to cut off.

Any hints on what prw Rail I should track first?

[reformatt]

Re: Dell Latitude E7440 FAN issue

I usually just put a probe on each coil when the fault occurs and see what is missing. Take note that CPU Vcore is at the end of the power sequence and requires all others to be functioning for it to be enabled. So if CPU Vcore disappears, make sure it's not because another sub rail before it has also died.

I did have a Dell machine (not this model) a few months back with a similar issue. In that case it was the +1V rail for the PCH that died intermittently. That turned out to be the boost capacitor for that buck converter had a broken solder joint at one end. So any flexion of the board would induce the fault.

Word of warning; don't go randomly probing around any buck converter (especially low voltage ones) with power enabled. Mess up the feedback and you'll end up with a dead PCH or CPU. With power off, physically inspect each component under a microscope for any movement and/or damage. A keen eye can sometimes reveal the fault.

[Shummi]

Re: Dell Latitude E7440 FAN issue

OK, now I have the Mainboar out again, it flickered and shut down once.
I have attached an Arduino Nano, and measure every second at:
+5V_ALW
+3.3V_ALW
+VCC_CORE
And now I cant get it to shut down, I have twisted it 15 min, and let it run an hour..... Just working.
I haven't attached HD, only FAN, RAM and LCD.
So my quistion is:
1. does it need more than
+5V_ALW
+3.3V_ALW
+5V_RUN
+3.3V_RUN
+1.35V_MEM
+0.675V_DDR_VTT
+VCC_CORE
2. As it dosn't seem to be a power issue, what could it then be?
This fault is frustrating....:-)