Latitude E7450 LA-A961P no power intermittent

[speggio91]

Hello all,

I have this laptop that won't power on 90% of the times I press the power button. When I plug the charger many times nothing will happen, in some rare occasion though, the led7 will blink once and then i'm able to power it on. The laptop will work until I power it off. If I remove and plug in the adapter again, there is an high chance that it won't power on again.

What did I do until now:
-disassembled it completely and extracted the main board looking for any obvious visible issues but no luck so far, the board is pristine and no previous job or water infiltrations were found.

-checked if the S5/S4 power rails are present:

+5V_alw is present
+3.3v_alw is present
+3.3v_alw_pch is not present
+3.3V_rtc_ldo is present
+3.3v_m is not present
+1.05v_m is not present


I've started to track down the origin of the +3.3V_alw_pch and:

UZ7 ic does not have voltage on Vin pin 1&2
so i checked if +1.05V_M is present on PJP300 and it's not.
I've checked both sides of PL301 and no voltage is there.
i've checled PR305 and PR312 and no voltage is there either.
I've checked PC302 PIN 1 and i measeured 2.4V and on pin 2 0V

Then i moved all my research on the IC PU300. The pin readings are:

1) 0V
2) 0V
3) 1.390V
4) 0V
5) 2.858V
6) 2.425pV
7) 3.3V
8) 13.6V
9) GND
10) 0V

Is it possible to have that voltage on PIN 8? Shouldn't it be the Adapter voltage?
I honestly don't know where to focus my research next, if you have any suggestion I would be happy to hear and understand more what's goign on with this board.

[MOD EDIT]
Schematic - https://www.badcaps.net/forum/showthread.php?t=73364
.

[Sephir0th]

Re: Latitude E7450 LA-A961P no power intermittent

13.6V at Pin 8 of PU300, the 1.05V Controller, should be normal, since it is NVDC Design. Means more or.less, Main Power Rail is battery rail at the Same time.

You already found out that a important Always Voltage, 3.3V_ALW_PCH, is Missing, so why going Forward in the sequence? Go Back to UZ7, the load Switch, and find Out what is wrong there.

Enable Missing? Voltage Inputs missing? Something Else wrong? Check Voltage of Pin 5 - 9 and Check also for internal short.

Regards

[speggio91]

Re: Latitude E7450 LA-A961P no power intermittent

13.6V at Pin 8 of PU300, the 1.05V Controller, should be normal, since it is NVDC Design. Means more or.less, Main Power Rail is battery rail at the Same time.

You already found out that a important Always Voltage, 3.3V_ALW_PCH, is Missing, so why going Forward in the sequence? Go Back to UZ7, the load Switch, and find Out what is wrong there.

Enable Missing? Voltage Inputs missing? Something Else wrong? Check Voltage of Pin 5 - 9 and Check also for internal short.

Regards

Thanks for your message!
I was focusing on PU300 because I thought it was more important since it is responsible for +1.05V_M line that goes into Pin 1&2 of UZ7 but I suppose that without the enable signal on pins 3& 5 of UZ7, nothing will turn on, right?

UZ7 has every voltage missing exept for VBIAS 5V and VIN 3.3V.
The chip seems to be fine, no internal shorts or shorts to ground was detected.
I tried to track down the PCH_ALW_ON but it goes to the KBC UE2 and probing it on pin A34 doesn't give me anything.

Does the RUN_ON signal must be present too or since it's not labelled with ALW it is not required?

[mcplslg123]

Re: Latitude E7450 LA-A961P no power intermittent

PCH_ALW_ON & RUN_ON-both are required for dc-dc transfer by UZ7 as they enable this
chip. Without these 2, you wont have any output from UZ7 on Pin 8-9 & 13-14.

[speggio91]

Re: Latitude E7450 LA-A961P no power intermittent

PCH_ALW_ON & RUN_ON-both are required for dc-dc transfer by UZ7 as they enable this
chip. Without these 2, you wont have any output from UZ7 on Pin 8-9 & 13-14.

Yes, that is true, but I think that during the S5 state only PCH_ALW_ON must be present in order to generate +3.3V_ALW_PCH_UZ7 from +3.3V_ALW line.
I'm quite confident about this because I measured on PJP29 after attaching the power supply to the board and waiting for the led7 to blink and I've got 3.389V.

Anyways, since the PCH_ALW_ON signal comes from the UE2, if it's not present it means something is up with that chip because it should be already programmed to always generate that signal.

I've tried to leave the board connected to the power supply and after some minutes the led7 blinked, PCH_ALW_ON signal generated and I was able to turn on the laptop.
If I disconnect the power supply and reattach it again right away it will still power on.
If I leave the board without any power and wait for at least half an hour, when I attach it to the power supply it won't give any sign of life until a couple of minutes and the LED7 will turn on.

I've attached the battery to the board and the behaviour was the same as when it is attached to the power supply. Once the led blink, the board also start to charge the battery.

This behaviour made me think about KBC issue or BIOS chip issue. I don't know if that make sense.
Another strange behaviour is that after pressing the power button and powering the laptop on, I must wait roughly 20 seconds before getting the Dell Logo and being able to accessing the bios.

The bios version is A10 which is very old compared to the latest version available A24.
I wanted to flash it on windows but unfortunately the owner put an admin password in the bios. I will ask him the combination and try to flash the bios to the latest version.
I will keep you posted, feel free to say your thoughts if you have any.

Thanks for your help

[mcplslg123]

Re: Latitude E7450 LA-A961P no power intermittent

Dell logo after 20 secs indicates problem with me region and flashing from windows environment may not fix it. Wiser to flash bios(clean me) with spi programmer.You can request for bios in bios section and remember to post your old dump. Hopefully, this should resolve the glitches you are facing.As far as your other observation, you are absolutely right that PCH_ALW_ON only should be present in S5 state. RUN_ON should come during transition from S5 state to S0 state.

[speggio91]

Re: Latitude E7450 LA-A961P no power intermittent

Okay, I will desolder and dump the two bios chips and post them on the bios section.
Is it right to reflash all two chips or I should just do the main one? I don't have experience with dell bios structure.
From schematics I see there is a 64mb Flash ROM and a 32mb one. Which one is the main and which one is the EC?

Thanks

[mcplslg123]

Re: Latitude E7450 LA-A961P no power intermittent

64 is main(8MB)
32 is EC(4MB)

You need to merge both the dumps to make a 8+4=12MB file and then clear me region. Once done, you again need to split it back to 8+4mb files.

Its advisable to flash both the files at one go to avoid version mismatch.

There are very capable members who'll do the job of cleaning me region for you.

[Vesko356]

Re: Latitude E7450 LA-A961P no power intermittent

Okay, I will desolder and dump the two bios chips and post them on the bios section.
Is it right to reflash all two chips or I should just do the main one? I don't have experience with dell bios structure.
From schematics I see there is a 64mb Flash ROM and a 32mb one. Which one is the main and which one is the EC?

Thanks

Try to flash both chips with the files from this post:
https://www.badcaps.net/forum/showpo...92&postcount=6

[speggio91]

Re: Latitude E7450 LA-A961P no power intermittent

Try to flash both chips with the files from this post:
https://www.badcaps.net/forum/showpo...92&postcount=6

Thanks for posting it. I tried the one from post #6 but I realised that were for non v-pro machine (the one I have is V-pro).
Then I flashed the two images from post #8. Once programmed and resoldered back the chips upon attaching the psu to the board nothing happened, no blink. I tried to press to power on and after few press it started powering up but I didn't have the screen attached to the board. So i detached the psu, attached the display cable to the board and after attaching the psu back I tried to press the button. This time nothing happened, neither after few presses or after waiting some minutes.
I will try again to reprogram the chips, I think when i detached the psu the first time I interrrupted something and bricked the bios.

Thanks anyway

[Vesko356]

Re: Latitude E7450 LA-A961P no power intermittent

Thanks for posting it. I tried the one from post #6 but I realised that were for non v-pro machine (the one I have is V-pro).
Then I flashed the two images from post #8. Once programmed and resoldered back the chips upon attaching the psu to the board nothing happened, no blink. I tried to press to power on and after few press it started powering up but I didn't have the screen attached to the board. So i detached the psu, attached the display cable to the board and after attaching the psu back I tried to press the button. This time nothing happened, neither after few presses or after waiting some minutes.
I will try again to reprogram the chips, I think when i detached the psu the first time I interrrupted something and bricked the bios.

Thanks anyway

Remove the bios battery and try again, the machine should auto start without pressing the power button, don't interrupt the process just wait few minutes, board should reboot few times and then will boot (if everything else is OK)

[speggio91]

Re: Latitude E7450 LA-A961P no power intermittent

Remove the bios battery and try again, the machine should auto start without pressing the power button, don't interrupt the process just wait few minutes, board should reboot few times and then will boot (if everything else is OK)

I did try to write both images from this forum again but even if I detached and reattached the bios battery, after i plugged in the psu nothing happened.

So, I did search for other dumps in the internet and I stumbled across two pair of old bioses (Main and EC) in a paid website . The first one made the machine turn on right after I plugged in the psu but after 30 seconds all status led powered on and the first one on the left (HDD status) started to blink. Accordingly to DELL, that mean there is a cpu problem. Since I think the CPU is in perfect conditions, I've gave a shot to the other pair of dump files.
That one did something, after pluggin in the psu the board started to boot automatically and after 20 seconds I had the DELL logo. I booted into windows and applied the latest bios available.

Now the machine seem to be back to normal, exept for the long wait between the power button press and the dell logo.
To be 100% sure the board is fixed I will leave it without any power (only with the bios battery) overnight, and hopefully tomorrow should be working.

I will let you know how it ends, thanks for your support and fingers crossed!

[speggio91]

Re: Latitude E7450 LA-A961P no power intermittent

Unfortunately, I was too optimistic. When I tried to power on the board today nothing happened, neither if I waited minutes.
Since this repair lasted too long and the owner want the laptop back, I will end my effort to fix it.
Looking around the board I couldn't find anything else to check exept for the KBC chip UE2 that is responsible for many ALW_ON signal that are not present. There is no way I could program that chip or find a replacement.

It has been a nice journey though, I've learned many things about power on sequence and power states.
I wanna thank all the users that contributed to help me and put their knowledge in this beautiful forum! I know I can find always help here.
Any failed repair can be helpful to understand and add a little more knowledge that can be used for the next repair.

Thank you all!