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Old 02-01-2022, 04:01 PM   #1
grimacelord
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Default Dell LA-C571P - Won't Charge - Battery 255%

Hello,

This motherboard reports that no battery is installed, although it will power on from the battery if there is a charge on it. It also will not charge the battery and reports the percentage at 255%.

I have replaced the battery twice with two different (but compatible) batteries and it behaves the same way. When the replacement battery arrives with a partial charge on it, it will power on the laptop, but the charger will not charge it and reports at 255%.

I believe this is a motherboard problem, but I am not quite sure where to look. Could someone help me figure this out?

Here is the schematic and PDF boardview (attached)
Attached Files
File Type: pdf DELLIN~1.PDF (1.18 MB, 11 views)
File Type: pdf COMPAL~1.PDF (396.3 KB, 8 views)
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Old 02-01-2022, 04:10 PM   #2
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Default Re: Dell LA-C571P - Won't Charge - Battery 255%

Quote:
if there is a charge on it. It also will not charge the battery and reports the percentage at 255%.
Perhaps a new Energizer battery ??


See attached. Meter in DC 20V scale (or similar).

Attach the battery and power adapter.

Measure and post the voltage on the battery SMB lines. There is the SCL (Clock) & SDA (Data) lines used by the SMB Host (Master) to ping the battery (SLAVE) to determine its stats.

255 decimal = FFh (hex). Guessing that the bus is reading back 255 as a value from the battery.
Attached Images
File Type: jpg smb_battery.jpg (102.0 KB, 12 views)

Last edited by mon2; 02-01-2022 at 04:31 PM..
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Old 02-01-2022, 04:37 PM   #3
grimacelord
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Default Re: Dell LA-C571P - Won't Charge - Battery 255%

Quote:
Originally Posted by mon2 View Post
Perhaps a new Energizer battery ??


See attached. Meter in DC 20V scale (or similar).

Attach the battery and power adapter.

Measure and post the voltage on the battery SMB lines. There is the SCL (Clock) & SDA (Data) lines used by the SMB Host (Master) to ping the battery (SLAVE) to determine its stats.

255 decimal = FFh (hex). Guessing that the bus is reading back 255 as a value from the battery.
3.3V on both of those.
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Old 02-01-2022, 04:48 PM   #4
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Default Re: Dell LA-C571P - Won't Charge - Battery 255%

Check the VFb (voltage feedback) pins on the charger IC. Use a battery with some charge if possible and check if the same voltage from the battery is reaching this IC.

What are the voltage readings for the battery connector ?

Are the contacts clean and the SMBUS pins are reaching the battery pack ?

Confirm that the SMBUS contacts are reaching the battery connector.

Confirm that the SMBUS contacts are reaching the charger IC.

That is, for both cases, after the resistors between these points of interest.
Attached Images
File Type: jpg Vfb.jpg (102.1 KB, 11 views)
File Type: jpg battery_connector.jpg (86.1 KB, 11 views)
File Type: jpg confirm_SMBUS_at_component.jpg (58.6 KB, 12 views)
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Old 02-02-2022, 08:47 AM   #5
grimacelord
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Default Re: Dell LA-C571P - Won't Charge - Battery 255%

Quote:
Originally Posted by mon2 View Post
Check the VFb (voltage feedback) pins on the charger IC.
Pin 15 VFB: 1.5mV
Same voltage on both sides of resistor PR726


Quote:
Originally Posted by mon2 View Post
What are the voltage readings for the battery connector ?
Not sure if you wanted these measurements with or without battery installed. Here are the voltage readings WITHOUT the battery installed.

01.GND
02.GND
03.SYS_PRES - 0V
04.BATT_PRS - 3.3V
05.DAT_SMB - 3.3V
06.CLK_SMB - 3.28
07.BATT1+ - 0.79V
08.BATT2+ - 0.80V

And then here are the same voltage readings WITH the battery and AC adapter connected:

01.GND
02.GND
03.SYS_PRES - 0V
04.BATT_PRS - 0V <---- Changed
05.DAT_SMB - 3.3V
06.CLK_SMB - 3.28
07.BATT1+ - 2.5mV <-----Changed
08.BATT2+ - 1.6mV <-----Changed

Quote:
Originally Posted by mon2 View Post
Are the contacts clean and the SMBUS pins are reaching the battery pack ?

Confirm that the SMBUS contacts are reaching the battery connector.

Confirm that the SMBUS contacts are reaching the charger IC.

That is, for both cases, after the resistors between these points of interest.
Contacts are indeed clean. 3.3V is reaching Pins 9 and 10 on charger IC.
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Old 02-02-2022, 02:02 PM   #6
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Default Re: Dell LA-C571P - Won't Charge - Battery 255%

Well, thanks for your help mon2. You lead me on the right track and I was able to solve it from there. The charging IC was to blame. I just so happened to have a donor board that had separate issues. I took the same measurements on that board and realized it was measuring properly, so I swapped the charging IC from the donor board to my patient board and it is now fixed! Thank you again!
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