HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

[loopster]

Hello all, I've got a defective HP Pavilion 15-cs1042ng here that won't turn on.
Unfortunately, there seems to be no boardview or schematic for this
model DA0G7EMBAE0 REV : E.

No adapter light when charger is plugged, battery not charging.
Voltage passes 1st and 2nd mosfet, nothing noteworthy on the battery charging circuit, except 1.0V on 4th pin of battery. Battery does not put out any voltage on the battery connector.

Got 19, 3.3V, and 5V rails, 3.3V on Bios chip and EC ITE8987VG,
but only 1.0V on the power button. No shorts anywhere on the board,
except for obvious low impedance on the GPU and CPU rails.

Spent quite a while figuring out where and what the 3.3/5.0V LDO on this board is. I think it must be a Richtek chip, markings are 4E=5G /H0F.

This chip got 19V in, puts out 5V (I guess, don't know any pinout),
and some 4.5V can be measured (maybe feedback?), but no 3.3V.

Can anyone confirm my guess that this obscure 4E=5G is the LDO,
and maybe point me to a relevant datasheet.
Thanks

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

Duh, I am probably mistaken. 4E=5G seems to be RT8813D, which ist
not a 3.3/5.0V LDO

https://cdn.badcaps-static.com/pdfs/...1cea85d5d2.pdf

I am at a loss here...

[reformatt]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

3V/5V coils are usually close to each other, and typically not close to any other major item like CPU/GPU/RAM. Buck converters can be individual for each rail or a combined IC. Without a close up of the board that's the limit I can tell you.

Another short cut is measure voltage on the caps around the EC. If you get 3V here, you most likely have your LDO present. It seems unlikely this would be missing if your main 3V/5V rails are present.

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

Thanks for your input, but I think I've caught the culprit now :-)

There is a QM3002M mosfet on the charging circuitry (I suppose it's the low-side mosfet connected to the Inersil charging control chip) which shows a short between gate and source. I suspect that's why the battery signal wire is pulled from 3.3V (when the battery is disconnected) down to 1.0V when plugged in.
Also the battery + connector pins have direct continuity with that gate pin, and that can't be right...?
Going to be a bit of a challenge replacing that component as the space is very tight around this location,
and I'm a hot-air and soldering beginner tbh, but I venture to say I am on the right track with my diagnose.
Time to practice on some scrap, and then take a deep breath maybe ... :-)

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

I've replaced the QM3002M mosfet, but it comes up as short between gate and source again. Checked the original mosfet as best as I could (it's tiny), and I think it was good after all.

Time to give up without a boardview and schematics, or does anyone have an idea? Attached the general datasheet about configuration with the ISL88739B control chip. Replace ISL88739B?

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

Found that Pin 14 and 15 of ISL88739B show continuity with each other, and both continuity to the gate of the QM3002M mosfet, and subsequently through to the coil and to battery + connector pins. Sadly, Renesas doesn't publish a full datasheet with pinout of ISL88739B. Gave ISL88739B mild reflow, didn't change anything. It has 19.5 going in, and shows some random readings, among them a stable 5V and 3.0V
Coulld ISL88739B be internally shorted and still "work" somehow?
Anyone has some moreinformation on ISL88739B?

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

If the configuration is similar to this schematic found in this thread
https://www.badcaps.net/forum/showthread.php?t=89239
Pin 14 and 15 of ISL88739B will show continuity as current sense lines.

What else can I check?

[mon2]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

Measure the voltage to ground of:

ACIN
ACOK
DCIN

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

Thanks mon2,
ACIN 2.2V
ACOK 3.0V
DCIN 19.2V

[mon2]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

ACIN is too low.

Remove all power. Meter in resistance mode.

Measure the resistance of the high side resistor.d

Then measure the resistance of the low side resistor on this pin.

Do the resistance values match the schematic values?

They work together to lower the adapter voltage to a safe value for the ACIN pin. From memory, it should be a higher voltage value.

If required, replace the high side resistor with a lower value. This will cause a less of a voltage drop to ideally trigger and pacify the charger IC.

Or, you can increase the low side resistor for the same result.

As we all know, resistance is futile...unless you are on Star Trek.

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

Unforunately, there aren't any resistors. The ACIN trace vanishes through a via into the board. And there are no component markings on the board anywhere.
Bit like a needle in a haystack, and you don't know what the needle looks like.

[mon2]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

Ok. Meter in diode mode. Remove all power.

Short the meter probes and the meter should tone beep. Confirm it.

Next, one probe on the ACIN pin.

The other probe on any nearby black body resistor. Check each pin of each resistor. When you hear the tone, you have found the ACIN resistors.

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

Yeah, should have checked the ones nearby. Found them easily.
High side is 418k, low side 58k, which looks good to me.
But shouldn't I be concentrating on the gate-source short of the QM3002M mosfet?
Gate is connected to pin 23 UGATE, and source to 22 PHASE.

[gs84]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

which voltage is here?

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

Sry, I don't know where to check this voltage on ITE8987, I don't have any schematics or boardview for this laptop,
and ITE8987 is a chip with no external leads. I am 98% sure ISL88739B is somehow duff.
I removed the QM3002M mosfet again, and the short between gate-source was gone.
When I measured gate to 23 UGATE, and source to 22 PHASE continuity with beeping (diode) mode,
the short on the gate-source pads reappeared, and pin 23 and 22 had like 60-70 ish Ohms between them.
The same behaviour was previously observable when the adapter was connected.
Low Ohms / continuity disappear and reappear with diode mode measuremnts on pin 23 and 22.
I don't think that ISL88739B is supposed to show internal capacitance...?
Anyway, I've ordered the chip and will give an update after replacement.

[gs84]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

here

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

You got the same laptop? Would it be safe to connect the adapter and measure the voltage with the QM3002M mosfet off the board? It's not turning on anyway?

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

I put QM3002M back on the board, just to be safe. I have 1V on the 2.2Ohm resistor.

[loopster]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

This diode feeding into ITE8987 marked yellow measures funny.

While all other diodes of the same type on this board measure 269 and OL in diode mode, this one measures 269 and 1350.
It's marked KN 500. Could this be the cause of the fault?
Can't find any datasheet on that type. Anyone knows whait it is, is it a Schottky diode? Could I replace it with a different type?

[Sephir0th]

Re: HP Pavilion 15-cs1042ng - unknown 3.3/5.0V LDO

Measurement of a diode IN-circuit is almost always inconclusive.

Your troubleshooting is way to random to reach any goal here in addition. it might even end contrary.

If the Main power rail is present, there is pretty sure no issue with the charging controller and if 3V/5V coils are present you pretty much don't have to worry about the LDOs.

You have to start with the basics instead. With a known good charger for example.