dell ddm90 la-f381p no power on adapter

[ahmarzo]

have dell la-f381p no power on adapter working fine with battery but not charging.first mosfet pq9 has 18v on gate.+3.3V_VDD_DCIN is missing and i have 1.6 v on pin 3 of lm393 and no voltage on all the pins.cant find schematics with same board no but have attached similiar schematic https://www.badcaps.net/filedata/fetch?id=2083398. any help is appreciated thanks

[mon2]

No charging can be that the power adapter is not recognized due to PS_ID pin. What does the BIOS report? Is the adapter attached and properly detected in the BIOS?

[ahmarzo]

Thanks for the reply mon2 but the laptop is not powering on with the adapter without battery and 19v does not pass through the first MOSFET I have changed the charging ic 88739a.the pq9 is p channel MOSFET if i am not wrong but I get 18v on the gate .

[mon2]

If you have such a high voltage on the gate, then the P-channel mosfet will remain disabled. Only if the P-channel gate is lower than the voltage on the source / gate pins will the mosfet enable. Having said this, suspecting one of the DCin mosfets is leaking (as per the article by piernov on charging circuits - see above sticky).

Remove all power. Meter in resistance mode.

Measure the resistance across the mosfet:

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. We are checking if the resistance is low, then the mosfet is defective. Each resistance check should be hundreds of k ohms or higher.

Repeat for the 1st DCin mosfet as well.

[ahmarzo]

hi thanks for reply both mosfets are not short and ic pq9 ic 88738h has no voltage on any pins.gate voltage on first mosfet is high laptop has only 19v dcin and 18.3 v on gate of first mosfet

[mon2]

Review post # 2. Need to know the voltages on the PS_ID line. Measure @ PL3.

What is the voltage to ground on pin # 17 of the charger IC? There must be a valid voltage here to power this charger IC.

[mcplslg123]

No point troubleshooting PS_ID at this stage as it cant work without the pull up 3V which will be generated only when 19V reaches CLR.
Focus should be on gate voltage of dc-in fets.

[ahmarzo]

hi after shorting pin 2 and 3 of pq6 i got 9 v on gate and laptop started working on adapter and i got display but the battery is not charging and i got 4.4v on ps_id.

[mon2]

4v4 on PS_ID is too high. This implies the mosfet on this PS_ID line is leaking. Replace the mosfet.