DELL Latitude 5410 - dead; pwrbtn flashing

[YellowJacket]

Hi folks,
DELL Latitude 5410, board number FDZ41 LA-J371P Rev: 1.0 (A00), schematic uploaded in different post, here is the link --> https://www.badcaps.net/filedata/fetch?id=3484415

When I connect it to a power ( DELL round charger, or USB-C ), LED on the power button starts flashing white, and the laptop doesn't do anything ( flashing slows for a very brief time in time when I press it, but it continues again ). Battery is not charging. While the charger is connected, I have few voltages present, but some of them are fluctuating, see attached pictures.
All I was able to figure out, was following the timing diagram in schematic ( page 5 ), and I had no issue with any voltage rail, until I came to `PCH_RSMRST#` signal ( 7th signal ) and this was the first position, where the fluctuation appears. PCH_RSMRST is deployed by EC chip, so now I am not sure, if there is an issue in EC ( not likely ), or in PCH or somewhere else. Its resistance to gnd is 60k.
I would be really thankful for any hint, what to check now.

[YellowJacket]

Guys ( especially you, Sephir0th ), you won't believe.

I fixed it. The issue was short at +3.3V_WWAN power rail, which is number 11 in power on sequence. I was stopped at number 7 = PCH_RSMRST#, because of its fluctuation. I stopped checking anything else later on. But then I realized, it is actually ON, but after then it shuts off from some reason. Firstly I though that its fluctuation is somehow an issue.
So I found shorted cap at +3.3V_WWAN and now the laptop runs fine. Thank you a lot for your time, I got a lecture - never stop checking every single voltage rail from power sequence.

Cheer guys

[mcplslg123]

The coil marked as 49K is the main power rail and should be 12-14V approx.It should be stable.

The reason you are getting fluctuations on RSMRST# pin is 'coz of fluctuation on this NVDC rail.

So look towards dc-in mosfets and charging area to make that coil voltage stable. Once you are able to fix that,it should start charging and may power on as well.

So going by the info provided by you, I'm almost sure your issue is in charging ciruit.

[YellowJacket]

Hi mcplslg123, you are indeed correct and I just figured it out yesterday, I didn't update the thread. I tried to measure both PQ700 and PQ701 dual channel mosfets out of the board, and they are good ( tested with diode mode both integrated transistors for each of G-S-D. They are opening and closing as they should ). Also tested the PQ702 mosfet for charging.
Measured values around the charging IC ( ISL9538CH ):
DCIN = 19V
VDD = VDDP = 5.16V
ACIN = 3.5V
ACOK = 3.1V

There are few waveforms measured around PQ701 ( attached pictures ), first two are input and output of PQ701, second two are gate signal of high side and low side of PQ701.

I suspect the ISL IC, even after watching this video --> https://youtu.be/yKwOsWSLTqg?t=2625 <-- quick recap = he actually had the same problem, with fluctuating main power rail. He swapped the charging IC ( also ISL9538CH ), with no change. But he had a short on one of power rails, what he didn't notice from the beginning. After fixing short, the board still acted the same, so he decided to swap the ISL again, and then board came alive. So looks like I am going to swap it too, and I will update this thread. If you have any suggestion though, before the IC arrives, let me know. Thanks so far.

[mcplslg123]

The measurements shared so far doesnt indicate a short on main rail and charging ic pin measurement shared are also perfect.
Yes, it could be bad charging IC but measurements so far dont indicate anything-so its wild guess for now.

[YellowJacket]

Well, the replacement IC is already ordered, so I will just change it, and if it doesn't solve the fluctuation, will dig more. The linked video assured me, that even healthy looking waveform from the charging IC could be somehow defective IC.

[YellowJacket]

I got the new ISL IC, replaced it, but there is no change, the main power rail is 8.6V, not +17.8V, like it is shown in schematic. I got new measurements around ISL, with the USB charger, here are results ( value marked with ~ indicates fluctuation at this pin. Its AC waveform with peak-to-peak value is attached ):
DCIN = 19V ~
VDD = 5V
ACIN = 3.4V ~
ACOK = 2.9V

Looks like you were right, mcplslg123 , and the power management chip is not the culprit. But now I am really lost. What should I check now? Why is the main power rail so low ( nice and smooth btw )? Can it be a short somewhere? Somewhere after one of SMPSs, which I measured ( with all "big" coils )? Thank you so far for your support.

// note, I am not testing the board with the battery connected, since it is probably flat and won't charge obviously, when it's connected

[m1ch43lzm]

Hi, check value of PR725, connected to pin 27 of the ISL9538, according to schematics should be 316K 1% 0402

8.6v means it's set for a 2S battery

What's the voltage rating on the battery label? As searching for latitude 5410 battery i get 4 different types of batteries with different voltage ratings

[mcplslg123]

So now volatge on charging coil is stable at 8.6V? If yes, thats a progress.
PCH_RSMRST# is still pulsing or is it stable now?
Btw, 8.6v as main rail may be correct as seen this type of volatge in many mb's.

[Sephir0th]

In NVDC designs the main battery dictates what voltage to expect. What is written in the schematics is not always a exact indicator for the expected voltage B+

I would continue with power rails which were ignored before. Preferably rails later in the sequence since even the RAM seems to start up, which indicates successful de-assertion of SLP_S5# - SLP_S3#

Which means S3/VS & S0 rails enbled by load switches but especially this missed 1.8VALW(?) rail (picture).

[YellowJacket]

Hi, check value of PR725, connected to pin 27 of the ISL9538, according to schematics should be 316K 1% 0402

8.6v means it's set for a 2S battery

What's the voltage rating on the battery label? As searching for latitude 5410 battery i get 4 different types of batteries with different voltage ratings

Hi.
- I can't locate the PR725 resistor ( boardview unavailable ), but I will try to locate it, it just takes some time. Onboard, it has value 78k2, but yeah, its onboard, it was expected, that value will be lower.
- battery nominal voltage is 15.2V ( "limited charging voltage" = 17.6V )

mcplslg123 - I probably confused you, but the main power rail was stable whole time, there was unstable only voltage at the output of the coil PL701 ( which is probably fine in NVDC mode ). If you look at second picture from my #3 post, you will see its waveform. Its the same whole time, even after replacing ISL IC. So yes, PCH_RSMRST# is still fluctuating.

Sephir0th Hi
- I have attached my notes from measuring all voltages/signals from power sequence. I was unable to locate the place of PCH_DPWROK ( only under EC or PCH ), but PCH_RSMRST# is fluctuating.
- the spot you circled out is 1.8V , nice and stable ( labeled as +1.8VALWP in my notes )

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

I will come back to ISL IC for a while, I would like to share some weird behavior ( maybe not ) around bootstrap. Bellow are attached two waveforms related to bootstrap, one is for BOOT1 pin, which is related to high side mosfet in first double mosfet in NVDC buck converter, another one is for BOOT2 pin, related to high side mosfet in second double mosfet. I don't know, is the waveform of BOOT2 normal? Isn't it the reason, why the output voltage is only 8.6? I replaced the bootstrap capacitor PC727, but still the same.
Big thanks to you, guys.

[Sephir0th]

Where is the resistance measurement of the 1.8VALW ?

Also check S3 and S0 rails ad suggested above

[YellowJacket]

Sorry

Resistance of the 1.8VALW rail is 2k8.
Not sure, what do you mean by S3 and S0. Like what signal. Do you mean SIO_SLP_S3# and SIO_SLP_S0#?

[Sephir0th]

No. These. Actual Power Rails. Never miss these when the fault isn't obvious.

[YellowJacket]

All selected power rails are fluctuating, see attachments. Only +0.6V_DDR_VTT is 0V. Resistances seem fine to me. Actually all enabled signals are fluctuating, obviously ( RUN_ON for example 0-1.9V ).

[Sephir0th]

This means the culprit could be even later in the sequence...

What about the CPU? Is it getting enabled with this fluctuating signal (VR_ON)?

Also interesting: Why is the 0.6V VTT not fluctuating like the others? Could be worth to check this supply more detailed too.

[YellowJacket]

CPU coils are all time low, VR_ON, I found only IMVP_VR_ON ( is it it? ), and it is at 0V. RUN_ON is fluctuating at 3.4V, SIO_SLP_S3# is also fluctuating at 3.5V. See the attachment.

I believe, I have to have 0.6V_DDR_VTT_ON_R (pin S3 of PU200) high in order to generate +0.6VSP ( which is 0V all the time ). That signal is although also fluctuating (attached. Also with S5 pin signal). The EC is the one, who deploys that signal.

PCH_RSMRST# is 3.5V fluctuating, PCH_PLTRST# is 0V.

[YellowJacket]

UPDATE:

I was able to charge a little the battery ( USB charger plugged in, then inject +17V directly to battery pin ). It took around 1.5A, but only for few seconds, maybe one minute max. Then it took no current at all. Vbat was 14V and main power rail 16.7! Although the board behaved exactly the same. The battery is not charged from the charger.
When I unplug the charger, the battery still connected, the LED on the power button is turned off ( in case of powering from the charger, LED is constantly flashing, like 0.5sec ON, 1sec off ). After pressing it, the LED turns on briefly and then turns off ( same like with the charger ). There is no voltage present except 3.3V LDO. After pressing the power button, all SMPSs start for a brief time and then shut off.

Another finding:

• from battery only - probing first pin of SPI ROM reveals, that there is some communication after pressing the pwrbtn. All time, after pressing it.
• from the charger - that communication at pin 1 is continuous.

I don't know, cannot it be BIOS related?. Just asking ( if I remember, there has to be also Vcore present in order to blame bios, but I don't know, if it is global rule ). I hope, this info would be helpful somehow, and we can at least pinpoint suspicious culprit together, guys.


// BTW, I tried bios rom --> #5 from this thread <-- but no success. Is it correct for my board, right?

[YellowJacket]

Guys ( especially you, Sephir0th ), you won't believe.

I fixed it. The issue was short at +3.3V_WWAN power rail, which is number 11 in power on sequence. I was stopped at number 7 = PCH_RSMRST#, because of its fluctuation. I stopped checking anything else later on. But then I realized, it is actually ON, but after then it shuts off from some reason. Firstly I though that its fluctuation is somehow an issue.
So I found shorted cap at +3.3V_WWAN and now the laptop runs fine. Thank you a lot for your time, I got a lecture - never stop checking every single voltage rail from power sequence.

Cheer guys