DELL LA-K661P power problem

[pc_okay]

Hello friends !

I have this laptop not charging ...(doing nothing)

Missing ACDET: 0V.

If i understand the schematic:
the AC_UVP_Protect is active and pull to low the ACDET with PQB2_GATE signal on PQB2 mofset.

I try to check the UV Protect:

• i found +19VB_UP_1 is high (3V)
• pulled high by PU601

You can see values of PU601 on the image.
I don't understand how this IC is supposed to work.
Can you help me please?


And can you tell me why compal call that Smokeless UVP ????
The owner is a big smoker, the card smell cold tabacco and is a bit dirty... could id be related???

Thank you.

[mon2]

Smokeless UVP

The name will be from a poor Chinese to English translation. For a good laugh, read some of the reviews on Aliexpress which are translated from Russian to English.

The takeaway here is 'UVP' = under voltage protection'.

Attach the power adapter. Carefully measure the voltage from the power adapter starting at the dual diode that feeds into the ~0v2 pin. Something is wrong here. Post each measurement starting with the input to the anode of the diode; after the diode at the cathode; then the voltage after each resistor that follows.

This mix of parts is creating a voltage divider to lower the rather high voltage of ~19v to a safe and lower voltage for PU601. Have not checked the expected voltage here but do not believe it is correct. To confirm the expected value, search for 'resistor based voltage divider calculator' and then input the R1 (high side) and R2 (low side) resistor values and the starting voltage from the power adapter. The calculator will spit out the voltage that you should see here if all is well.

If ACDET is 0v, nothing will happen with the power adapter as the adapter is deemed to be disconnected.

[pc_okay]

Hey Mon thank you.

Weird board, the AC_OK is back and 3V on power button too, but not power on.

There is a weird sticky liquid without oxydation around GPU mofset.
I ultrasonic the board, I'll check it again on monday after a good dry.

Have a good week-end !

[pc_okay]

Hello Mon,

I was tired i think on saturday, because laptop was working and still working today for a few minutes. (i was thinking laptop was not starting because fan was not spinning.... my bad)
But again latptop stop working taking power and ACDET is down again.
It's the second time laptop do this, first time, i had just unplugged battery wait and laptop revive for a few minutes too.

I take some measurement again.
I think i made an error on saturday on the voltage divider i get now 0.772V and when the laptop is working i get around 4V.

I just see on the left of the diagram some information, LATCH V - : 0.87V.
If I understand correctly, IN- must be > 0.87V ? but with a voltage divider with 3.3V and 1Mohm and 332kohm i get 0,82V....
And i can't get +19VB without ACOK....
What i am missing?

Thank you !

[piernov]

Latching comparator circuit.
If IN+ > IN- → OUT = 3.3V and stays there. Resets when IN- > 3.3V, i.e., +19VB > 13.5V. Not sure how that's supposed to happen if charging circuit is turned off.
At power-up, HW_ACAV_IN = 0 and +3.3V_ADP_DCIN = 3.3V so IN+ < IN-, so OUT = 0, until charger initializes then both HW_ACAV_IN and +19VB come up but stay in IN+ < IN- configuration. IN+ needs to come up after IN-, which is achieved by RC circuit PR606/PC603.
I hope I'm reading that right. To be honest I don't know what they are trying to achieve with that circuit.

[pc_okay]

Ok i forget to tell something strange, i Have 2.6V on +19VB line.
Something must leak somewhere?
I cherck all charge mofset + batfet, i have 0V on all gate.

When i plug the AC adapter (without battery) i have around 4-5V +19VB decreasing in 5 second to get fixed at 2.6V.
When i unplug ac adapter (without battery) voltage slowly decrease to 0V, it takes like 1 minute to decrease.

I'm pretty lost now...

[mon2]

Review the voltage to ground on the source (1-2-3) pins of the mosfets @ PQB11 and PQB12. Is there a voltage here? If yes, then the same voltage is passing through the internal diodes inside of PQB13 and PQB14.

[pc_okay]

Sadly no... for first pair of mofset 11 et 12 i get 19.75V on pin 5, 0 on pins 1,2,3,4.
For second pair of mofset 13 et 14 i get 0V on pin 1,2,3,4 and 2.60V on pin 5

[pc_okay]

i forget to post my IC voltage, here attached.

[mon2]

If ACIN = 0v then this may mean that PQB2 is conducting. Check the gate voltage on PQB2. Consider to flux and remove PQB2 for testing.

[pc_okay]

With PQB2 remove: same leak of 2.6V and DCIN & VDDP down. 😭

[mon2]

What is ACIN with PQB2 removed?

[pc_okay]

2.41V

[pc_okay]

Hello friends,

So after diging, thinking, removing a lot of mofset and diodes... i foud the source of the +19VB leaking. (2.6V)
Without diode PD604 the +19VB line is clean.
And of course now the IC charge is happy and open every charge mofsets properly. (if i'm right IC charge don't like to see voltage on schunt resistor with close mofset)

But i don't like to not understand what i'm doing and i think it might be dangerous to cut this UVP/OVP protection.
Any thout on this? please find attached location of PD604 and schematics:

https://www.badcaps.net/forum/troubl...s-and-brd-file

Thanks !

[piernov]

With this diode it is normal to observe a voltage on +19VB all the time.

Let's assume Schottky diode drops are 0.2V.

Let's say if +19VB was 0V due to a short to ground, then VB_DETECT will be around 0.2V, so Vgs of PQ601A is 2.9V which should be enough to turn it on. In that case VB_SHORT# is pulled to 0.2V, which turns off PQ601B, so that VB_SHORT is pulled up to 3.1V. Therefore PQB2_GATE will be 2.9V, so that ACIN_CHG is pulled to 0V.

If there is no current across PD604 at all, then +19VB is above 2.9V, VB_DETECT is 3.1V, Vgs of PQ601A is 0V so it is turned off. VB_SHORT# is pulled up to 3.1V so PQ601B turns on, so VB_SHORT is pulled to 0V. Therefore PQB2_GATE is 0V (assuming nothing comes from +19VB_UVP_1 either), so ACIN_CHG is not pulled low.

Removing PD604 prevents any current from flowing across it, effectively disabling this discrete +19VB short circuit protection.

[pc_okay]

Thank you Piernov, thanks to you I now understand that if there is a short on +19VB, 19VB will suck up VB_DETECT and pull VB_SHORT# to 0 and etc. 😀

But in normal condition there is always that +3VALW_AC_DC that flow through PD604 to +19VB and mess the IC Charge. (i think)
Maybe i'm missing something or something is wrong elsewhere?

[piernov]

If battery is plugged in, you'd have battery voltage on +19VB anyway.
Something is probably wrong in the charging circuit.