DELL VOSTRO 14 - LA-D822P Rev: 1.0

[BishopCaps]

hey all

got this laptop and its being a pain.
Usual BIOS looking issue - Fans spin up, screen black.

Reflashed the BIOS, got it to boot up fine, input service tag etc all working ok.
Sat over night, plugged in to image it and same exact issue again.

Any ideas?

Thanks
Anthony

[mcplslg123]

Re: DELL VOSTRO 14 - LA-D822P Rev: 1.0

Is the SOC located very near to Bios chip?? Try again heating on the bios chip and see if you get display. I think it was not bios but perhaps due to heat applied during soldering which is at play. Look for corrosion on mb carefully.

[BishopCaps]

Re: DELL VOSTRO 14 - LA-D822P Rev: 1.0

Thanks buddy!

No soldering done - used a clip.

I was the first to open this machine too, which displayed these symptoms out of no where.

Any ideas?

[reformatt]

Re: DELL VOSTRO 14 - LA-D822P Rev: 1.0

Check CMOS battery voltage. Does laptop start after a CMOS reset? Usually I'd try replacing the BIOS EEPROM (W25Q128FVSIQ) on spec. Normally when they're defective, they won't erase properly or you get errors during verify.

[BishopCaps]

Re: DELL VOSTRO 14 - LA-D822P Rev: 1.0

Hi buddy.

CMOS reset has no affect. Only a full bios rewrite with verify. No errors found.

[reformatt]

Re: DELL VOSTRO 14 - LA-D822P Rev: 1.0

What BIOS version are you using? The OEM's have been issuing a number of BIOS updates recently to patch vulnerabities and some from Dell have been buggy. Use an earlier version to rule it out.

Failing that, have a look at the supply rail for UC2. +3V_SPI is derived from +3VALW so check this rail for voltage/noise. Decoupling near the IC could be an issue, check CC9 or add caps near UC2. If it's still U/S, replace UC2 and retest.

[BishopCaps]

Re: DELL VOSTRO 14 - LA-D822P Rev: 1.0

Hi people

Managed to flash it and get it working with a new CMOS. It won’t charge the battery, windows says it has 30% and verified battery working in another machine but it dies as soon as unplugged since the flash

[mon2]

Re: DELL VOSTRO 14 - LA-D822P Rev: 1.0

1) If you pre-charge the battery in another unit, does this logic board report a proper charge level ?

2) Will the pre-charged battery allow this logic board to function ok ? Just will not charge ?

3) See attached. Remove all power (no battery). Meter in resistance mode.

Check the resistance across the pins on the mosfets linked to the battery.

Measure:

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


Post the readings for the

mosfet PQ704 (aka high side mosfet)
mosfet PQ708 (aka low side mosfet)
* the above 2 dial up the charge voltage for the battery pack.

mosfet PQ717 (aka battery mosfet) - used to power the logic board in the absence of the DC power adapter.

4) After the above measurements, attach a battery with some level of charge. Also attach the external power adapter. Meter in DC volts (20v scale is ok).

Measure (with care so there are no shorts) with red meter probe on point to test; black meter probe to ground.

a) Post the voltage readings on source (1-2-3 - any of these pins is ok since they are grouped together) of PQ704; gate (4); drain (5-6-7-8).

b) Then perform the same test on PQ708.

c) Final test for now is to check the current sense resistor @ PR765.

See attached. The charger IC is looking for the difference of voltage drop across this current sense resistor. On a case earlier this year, took ~3 weeks to locate that a trace was broken from the current sense resistor to the charger IC due to corrosion. This lack of voltage feedback from the battery on the charger IC made the IC believe that too much current is being drawn so shut down the charging feature.

On this note, does Windows show the charging graphic when you attempt to charge the battery ?

You can confirm the current traces by removing all power / no battery -> wait for the logic board to discharge for a few minutes. Then use the resistance scale (lowest scale on your meter) -> measure the resistance from PR765 to the charger IC pin itself. Measure right to the solder point on the IC. Do this for each leg of the current sense circuit (CSON & CSOP).

Again, this resistance check is without any power; then use the meter. It is a safe way to test in case the meter probes slip.