Dell Latitude 5480 - No 3v & 5v

[elfelvin]

I have a Dell Latitude 5480 which has power going in (charger stays lit) but no indication of life from the switch or the switch LED.

On inspection I can see that I am getting 12.5v to the power 3v and 5v IC's, PU100 and PU102, however I am seeing nothing coming out. I believe these IC's are where the 3v and 5v rails are meant to start?
Is there another pin on these IC's which should be toggled to trigger these IC's to start feeding power? Any help / pointers will be appreciated.

PQ9
Pin 4 - 9v
Pin 5 - 20v

PQ4
Pin 1,2,3 - 19.86v
Pin 4 - 19.86v

PU901 (ISL88738)
Pin 3 - 12.5v (VSYS)

PU100 (SY8288BRAC)
Pin 2,3,4,5 - 12.5v (+PWR_SRC)
Pin 17 - 0v (+3.3V_ALW2)
Pin 19 - 0v (+3.3V_ALWP)
Pin 20 - 0v (+3.3V_ALWP)

PU102 (SY8288CRAC)
Pin 2,3,4,5 - 12.5v (+PWR_SRC)
Pin 15 - 0v (+5V_ALW2)
Pin 19 - 0v (+5V_ALWP)
Pin 20 - 0v (+5V_ALWP)

[mielta]

Re: Dell Latitude 5480 - No 3v & 5v

Hello
I mean +PWR_SRC must be 19v with charger

[elfelvin]

Re: Dell Latitude 5480 - No 3v & 5v

Okay, what was throwing me off was another post (https://www.badcaps.net/forum/showthread.php?p=978407) which mentioned that 13v should be okay on the +PWR_SRC - I may have misinterpreted this. Let me check back at PU901 (ISL88738) to see if I can spot something there.

[elfelvin]

Re: Dell Latitude 5480 - No 3v & 5v

Looking at all the pins on PU901 (ISL88738), I can see that PIN 20 (OTGEN/CMIN) is shorted to ground. PIN 18 is NOT shorted. Which makes me think (being a novice) would it not be best / less intrusive to first take off PR960, as it is either this resistor or PU901 which is shorted?
Trouble is that I have no idea where PR960 is on the board... anyone with a boardview who can help?
Alternatively, i am sure others may just say go straight for the charger IC and replace PU901?

[mon2]

Re: Dell Latitude 5480 - No 3v & 5v

see attached.

Also from my understanding, either PR960 OR PR919 will be stuffed.

PR960 (0 ohm, 0402) shunts this logic line to ground.

PR919 (0 ohm, 0402) shunts this logic line to Vdd (+V).

So both of these parts should not be stuffed on your PCBA. Please confirm.

[elfelvin]

Re: Dell Latitude 5480 - No 3v & 5v

I dont have any physical resistors in these locations, all I have are tracks.
I have highlighted the "test points" which are grounded.

This surely means that PU901 is at fault, as there is no PR960 / PR919?

[Sametbey]

Re: Dell Latitude 5480 - No 3v & 5v

It can be rezerve for different use. How many volts do you see on the PR901 resistor? Is there AC_OK 3.3v on the 3 pins of the pu901 IC? In order to output ALW voltage in Pu100, there should be 3.3V at 12 pins (from IO)

[elfelvin]

Re: Dell Latitude 5480 - No 3v & 5v

PR901 - 19.8v

Below are the pins i managed to find voltages on. Which 3 pins should have 3.3v?

PU901
Pin 1 - 12.6v (CSON)
Pin 2 - 12.6v (CSOP)
Pin 4 - 5.2v (BOOT2)
Pin 7 - 5.1v (LGATE2)
Pin 8 - 5.2v (VDDP)
Pin 9 - 5.1v (LGATE1)
Pin 12 - 5.2v (BOOT1)
Pin 13 - 9.1v (ASGATE)
Pin 14 - 19.8v (CSIN)
Pin 15 - 19.8v (CSIP)
Pin 16 - 19.8v (ADP)
Pin 17 - 19.7v (DCIN)
Pin 18 - 5.2v (VDD)
Pin 19 - 3.6v (ACIN)
Pin 24 - 3.1v (ACOK)
Pin 28 - 1.4v (COMP)
Pin 31 - 12.4v (VBAT)
Pin 32 - 12.6v (BGATE)

[elfelvin]

Re: Dell Latitude 5480 - No 3v & 5v

PU100
Pin 12 - 2.7v (which should be the logic coming from MEC1501)? Not quite 3.3v though!

[mcplslg123]

Re: Dell Latitude 5480 - No 3v & 5v

Hello
I mean +PWR_SRC must be 19v with charger

Dont you think its NVDC technology used here?? In that case PWR_SRC will be +13V. Whats your opinion friend??

[elfelvin]

Re: Dell Latitude 5480 - No 3v & 5v

I believe the issue is with PR102.
When i measure continuity between pin 2 on PR102 and PWR_SRC, I get nothing. There seems to be a dry joint between pin2 and the board. I will confirm the outcome once this has been fixed.

[elfelvin]

Re: Dell Latitude 5480 - No 3v & 5v

I replaced PR102 with a 499K and now both 3v and 5v rails are working. The laptop powers on and peace has been restored in the world.
Thank you to all that commented, hopefully the diag helps someone in the future!

[Timeeez]

Re: Dell Latitude 5480 - No 3v & 5v

I replaced PR102 with a 499K and now both 3v and 5v rails are working. The laptop powers on and peace has been restored in the world.
Thank you to all that commented, hopefully the diag helps someone in the future!

Thanks a lot, I just got the same with LAT 5490. Seems to be a common problem on these models.

[Honziq]

Re: Dell Latitude 5480 - No 3v & 5v

see attached.

Also from my understanding, either PR960 OR PR919 will be stuffed.

PR960 (0 ohm, 0402) shunts this logic line to ground.

PR919 (0 ohm, 0402) shunts this logic line to Vdd (+V).

So both of these parts should not be stuffed on your PCBA. Please confirm.

Hello,
I have similar problem, laptop was water damaged.
After cleaning it woks from battery/not charging, but only until battery died.
I replaced some rotten resistors, now its recognized by USB-C charger, but it's stils dead.
I got 3,3V, but not 5V ALW.
On PU901 PIN3 i got 0V. I can't find PR929 on that board.

What can cause such problem?
What program you use for opening .cad BDV files?

Thanks.

[mon2]

Honziq - which model of laptop? Which silk screen markings are on your board?

Found it. PR929 has an '@' symbol = do not stuff on the PCB. So this part is missing by design.

Locate PU901 on your logic board -> locate pin # 3 -> share pics of this area. With PR929 missing on the board, this implies that there should be a solder blob to feed +PWR_SRC onto pin # 3 but confirm it. That is, there should be a pcb 'jumper trace' to bridge the adapter voltage onto pin # 3 of this charger IC.

[Honziq]

Honziq - which model of laptop? Which silk screen markings are on your board?

Found it. PR929 has an '@' symbol = do not stuff on the PCB. So this part is missing by design.

Locate PU901 on your logic board -> locate pin # 3 -> share pics of this area. With PR929 missing on the board, this implies that there should be a solder blob to feed +PWR_SRC onto pin # 3 but confirm it. That is, there should be a pcb 'jumper trace' to bridge the adapter voltage onto pin # 3 of this charger IC.

Markings are CDP70 la-e141p.
I don't have quality photo, but i will send it as soon as possible.
Pin 3 goes immediately to another layer of PCB.

[mon2]

See attached. The case is similar to the OP. This rail is at the end of the main power path from the external power adapter. If it is not enabling, you must review the voltage from the source to this area. Need to check each mosfet in the path. Since the battery was able to power the board, we know the main power rail is not shorted and the fault is between the DCin power connector and this target +PWR_SRC junction.

Start with reviewing the voltage to ground of

PQ905, pin #1 ; this must be the raw voltage from the power adapter
PL902 ; either side of the inductor
PQ904 ; pin #1 = +PWR_SRC

There are 2 mosfets inside of PQ904. Each is a suspect. Remove all power. Meter in resistance mode.

Measure the resistance across:

source / drain
source / gate
gate / drain

for each of the 2 mosfets inside this package. Checking for a low resistance which means this mosfet is defective.

[Honziq]

Thank You very much.

That mosfets I tested before, they are OK.
But I measure that voltages and on pin 1 of PQ 905 was 19V and behind PQ905 and on PL902 was 0V.
So I desoldered it and solder it back and now board is booting.

But PL902 making some weird loud whistling noises on boot. After some time it stops. And its only 9V on it.
So it looks like a problem of some capacotors around.
Or do you have suggestion why it making that loud noises?

Thanks.