HP Envy 15-W x360 448.04805.0021 Intermittent Boot

[mullspeed]

I've got this board to repair, it is intermittent to boot. If you leave it without power for about a week then it will boot first time but not again unless you leave it. It really needs a few days, overnight is not enough for it to reset!!!

I've reflashed the bios with the latest .bin by removing the IC, but get the same result as with the original BIOS.

I noted that when I attach power for the first time after leaving the board unpowered I get 7 white flashes on the charge LED (no battery attached, literally the motherboard with some RAM on the bench, connected to an external monitor) and the board will boot. The next time I apply power the I get a rapid orange LED but no booting and then after that I get a solid orange LED but no booting.

I have confirmed that the power button is switching from 3V3 to 0V and the charger output (no battery) is 12.5V.

Could it be the KBC IC? I've no idea where to start on this?!

[mon2]

Re: HP Envy 15-W x360 448.04805.0021 Intermittent Boot

Link or post the schematic and/or board markings.

If not available -> locate the power in DC connector -> review the mosfets that should be nearby (likely 2 of them) -> and the charger IC should be close to the mosfets.

The surface mount markings of the charger IC are important - probably 'BQ' (now a TI company; formerly BenchmarQ).

[mullspeed]

Re: HP Envy 15-W x360 448.04805.0021 Intermittent Boot

Board is Laduree1.0 MB 14257-2 448.04802.0021

[mullspeed]

Re: HP Envy 15-W x360 448.04805.0021 Intermittent Boot

Charger IC is BQ24737

[mullspeed]

Re: HP Envy 15-W x360 448.04805.0021 Intermittent Boot

SCH attached

[mon2]

Re: HP Envy 15-W x360 448.04805.0021 Intermittent Boot

Ok. Review this thread which is similar:

https://www.badcaps.net/forum/showthread.php?t=62235

From the datasheet that is available from TI, we can approximate what is going on with your logic board. TI does private label parts for OEM accounts so some are in the witness protection program.

With great care, measure the voltage on the mosfet pins that are close to your DCIN power connector. As per sticky above from @Piernov, you should find 2 x DCin mosfets.

We are interested to know the voltages on each pin of each mosfet.

Pins 1-2-3 = SOURCE pins ; pick one
Pin 4 = GATE
Pins 5-6-7-8 = GATE pins ; pick one

Often first or second or maybe both mosfets get damaged and need to be replaced.

They are very inexpensive (~1 USD) but will require tools and patience to replace.

You may have some bad caps on the board but TBD. Bad caps draw too much current and the current sense circuit will shut down the power supply leg.

[mullspeed]

Re: HP Envy 15-W x360 448.04805.0021 Intermittent Boot

Both Fets have 19.7V on drain and source and 6.5V on the gate, which is what is expected as per the circuit on P44 (the gate voltage I mean)

[mullspeed]

Re: HP Envy 15-W x360 448.04805.0021 Intermittent Boot

I also have a board for spares, so I've swapped the BQ chips over but there is no difference to the voltages on the board or operation of the board.

[mon2]

Re: HP Envy 15-W x360 448.04805.0021 Intermittent Boot

These charger ICs use N-channel mosfets. Being N-channel, the gate needs to be ~6 volts higher than the voltage on the source.

So the mosfet requires ~25 volts to ENABLE for this case (19v + 6v).

If you do not have 25 volts (approx) then the charge pump inside the charger is not working or is not enabled.

To investigate further, need to know the voltage on each pin of the charger IC. These measurements will help to diagnose if the charger IC is working properly or not.

[mullspeed]

Re: HP Envy 15-W x360 448.04805.0021 Intermittent Boot

The FETs in the schematic are P channel.

I'll get some more measurements tomorrow, thanks for your help so far.

[mon2]

Re: HP Envy 15-W x360 448.04805.0021 Intermittent Boot

A bit unique setup for the 2 x DCin mosfets.

The first one is indeed P-channel. So this means the gate voltage should be NEGATIVE (lower voltage) than the source to enable. This enable function is performed by the mosfet 2N7002 @ PQ4401. When PQ4401 is enabled with a positive voltage at the gate of this mosfet, then the gate of PU4401 is pulled to a lower potential due to the resistor @ PR4406 building up a voltage divider since it is now connected to ground -> voltage @ pin 4 junction will become lower than the DCin voltage of 19v forcing the mosfet PU4401 to enable.

The 2nd one is N-channel and driven directly by the charger IC. The boosted voltage on the gate pin #4 is still required.

Datasheets for both mosfets are attached.

Tomorrow, also remove all power -> measure the resistance across the mosfet pins so we can check if they are defective or not.

source & drain
source & gate
gate & drain