LG gram - Not Charging

[Ado02]

Hi,

I am working on an LG gram with a charging issue. The battery was replaced, but the problem didn't go away.

Charging IC: ISL95520

ACIN (Pin 1): 3.2v
ACOK (Pin 2): 3.2v
DCIN (Pin 18): 19v
VDD (Pin 19): 5v
CMRSC (Pin 29): 19v

Charger plugged in: MOSFETs short to ground / and caps in region of r439

I look forward to your help

[mon2]

Re: LG gram - Not Charging

Never measure resistance to ground with power to the board. Power to the people is ok.

Confirm it.

[Ado02]

Re: LG gram - Not Charging

Never measure resistance to the ground with power to the board. Power to the people is ok.

Confirm it.

I didn't know that. I am still learning.

I can't find a short when the charger is not plugged in.

[mon2]

Re: LG gram - Not Charging

Does the unit power up ok with the adapter ?

Fault is that the battery is not charging?

Does the graphic show that the battery is charging ?

[Ado02]

Re: LG gram - Not Charging

Does the unit power up ok with the adapter ?

The fault is that the battery is not charging.

Does the graphic show that the battery is charging ?

The laptop powers on with the charger. The laptop will stay on when the charger is plugged out. However, it will not power on with just the battery. This is a new battery with 48% charge - but when the charger is plugged out, Windows prompts "low battery". When the charger is plugged in - under the battery icon, I just get 'plugged in'.

[mon2]

Re: LG gram - Not Charging

Link or post the schematic if available.

When the charger is plugged in, does the battery icon show the charging graphic?

Is the battery a known good battery?

So battery is @ 48% and discharging since it fails to charge?

Measure, with care, the voltage to ground on each pin of the battery connector with the battery charger attached.

[Ado02]

Re: LG gram - Not Charging

Link or post the schematic if available.

When the charger is plugged in, does the battery icon show the charging graphic?

Is the battery a known good battery?

So battery is @ 48% and discharging since it fails to charge?

Measure, with care, the voltage to ground on each pin of the battery connector with the battery charger attached.

Battery: Is brand new and measures 7v

Charger plugged in - shows charging graphics - stops and message says plugged in.

Battery connector:

3 + Pins: 0.6v
Signal Pins: 3.3v

7v goes to first MOSFET (see attached image) (one above C310 marking)

2nd mosfet 0.6v on both ends, including gate.

C333, C327 and C334 - 7v

[mon2]

Re: LG gram - Not Charging

Post the full topside markings of the mosfet so we can review the datasheet.

[Ado02]

Re: LG gram - Not Charging

Post the full topside markings of the mosfet so we can review the datasheet.

As requested. Thank you.

[mon2]

Re: LG gram - Not Charging

See attached for the datasheets for each mosfet.

1) AON7400 is a N-channel mosfet. So pin # 4 (Gate) must be HIGHER than the voltage being passed between source & drain pins.

2) AON7405 is a P-channel mosfet. So pin # 4 (Gate) must be LOWER than the voltage being passed between source & drain pins.

3) Can you measure the voltage on each pin (group) again and post the readings?

source (1-2-3) ; pick any
gate (4)
drain (5-6-7-8) ; pick any

[Ado02]

Re: LG gram - Not Charging

See attached for the datasheets for each mosfet.

1) AON7400 is a N-channel mosfet. So pin # 4 (Gate) must be HIGHER than the voltage being passed between source & drain pins.

2) AON7405 is a P-channel mosfet. So pin # 4 (Gate) must be LOWER than the voltage being passed between source & drain pins.

3) Can you measure the voltage on each pin (group) again and post the readings?

source (1-2-3) ; pick any
gate (4)
drain (5-6-7-8) ; pick any

7400A

Pins 1-2-3 / 0.2v
Pin 4 / 0v
Pin 5-6-7-8 / 7.18v

7405

Pins 1-2-3 / 0.66v
Pin 4 / 0.63v
Pins 5-6-7-8 / 0.2v

[mon2]

Re: LG gram - Not Charging

So with Pin 4 = 0v, 7400A mosfet cannot turn ON.

Can you post or link the schematic for this logic board?

If not available, you will have to trace where the GATE pin travels on the board and this will likely be a (black body) resistor. The resistor will then be driven by the charger IC.

The charger IC will offer the boosted voltage to enable this mosfet.

[Ado02]

Re: LG gram - Not Charging

So with Pin 4 = 0v, 7400A mosfet cannot turn ON.

Can you post or link the schematic for this logic board?

If not available, you will have to trace where the GATE pin travels on the board and this will likely be a (black body) resistor. The resistor will then be driven by the charger IC.

The charger IC will offer the boosted voltage to enable this mosfet.

I traced the pin 4 (gate) to pin 25 BGATE (0v charger / no battery).

With the battery plugged in I get 11v on the pin 4 (gate) and 7v across the 2nd Mosfet.

Will the power pass to the battery connector if the battery is not connected?

Also, do you have any other suggestions?

[mon2]

Re: LG gram - Not Charging

Then BGATE has a valid voltage to enable to the battery mosfet. If the battery is not detected, the charger IC will not enable this mosfet.

This battery mosfet is like a solid state (no moving parts) on/off switch for the battery voltage - to power the logic board.

This mosfet should be enabled to power the logic board when the power adapter is not connected to the logic board.

Attach the charger and still keep the battery on the logic board.

Measure again the gate voltage to ground on this mosfet. Post the measurement.

[Ado02]

Re: LG gram - Not Charging

Then BGATE has a valid voltage to enable to the battery mosfet. If the battery is not detected, the charger IC will not enable this mosfet.

This battery mosfet is like a solid state (no moving parts) on/off switch for the battery voltage - to power the logic board.

This mosfet should be enabled to power the logic board when the power adapter is not connected to the logic board.

Attach the charger and still keep the battery on the logic board.

Measure again the gate voltage to ground on this mosfet. Post the measurement.

7400A Pin 4 / 12.9v
7405 Pin 4 / 2.26v

I also found 2 more Mosfets on the other side of the connector. Please see the image

Q23

Charger / no battery

Pins 1-2-3 7.16v
Pin 4 7.16v
Pin 5-6-7 19.11v

Battery No Charger

Pins 1-2-3 7.62v
Pin 4 7.62v
Pin 5-6-7 7.11v

Battery + Charger

Pins 1-2-3 7.22v
Pin 4 8.22v
Pin 5-6-7 18.98v


Q25

Charger / no battery

Pins 1-2-3 0v
Pin 4 0v
Pin 5-6-7 7.18v

Battery No Charger

Pins 1-2-3 0v
Pin 4 0v
Pin 5-6-7 7.62v

Battery + Charger

Pins 1-2-3 0v
Pin 4 0v
Pin 5-6-7 7.47v

[mon2]

Re: LG gram - Not Charging

Test to see if these new mosfets are leaking.

Remove all power.

Meter in resistance mode.

Measure the resistance across the mosfet pins.

Source (1-2-3) & Drain (5-6-7-8)
Source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post each measurement.

[Ado02]

Re: LG gram - Not Charging

Test to see if these new mosfets are leaking.

Remove all power.

Meter in resistance mode.

Measure the resistance across the mosfet pins.

Source (1-2-3) & Drain (5-6-7-8)
Source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post each measurement.

I am not sure if negative and positive probs need to be in some order.

The multimeter was set to continuity with the diode mode.

Q23

Pins 1-2-3 (N) - 4 (P) / 490
Pins 1-2-3 (P) - 4 (N) / 0 Beep

Pins 1-2-3 (N) - 5-6-7 (P) / 500
Pins 1-2-3 (P) - 5-6-7 (N) / 1 (No change on the meter)

Pins 4 (N) - 5-6-7 (P) / 1294
Pins 4 (P) - 5-6-7 (N) / 1 (No change on the meter)

Q25

Pins 1-2-3 (N) - 4 (P) / 440
Pins 1-2-3 (P) - 4 (N) / 996

Pins 1-2-3 (N) - 5-6-7 (P) / 420
Pins 1-2-3 (P) - 5-6-7 (N) / 1 (No change on the meter)

Pins 4 (N) - 5-6-7 (P) / 1200
Pins 4 (P) - 5-6-7 (N) / 1 (No change on the meter)

[mon2]

Re: LG gram - Not Charging

Meter in resistance mode.

..

[Ado02]

Re: LG gram - Not Charging

..

Sorry to be a pain but which is the best one?

[mon2]

Re: LG gram - Not Charging

Start with the 200k scale. If you do not get a reading, go higher.

If the resistance is too low, the mosfet is defective.