Hello everyone, I need your help. I'm having issues with a Lenovo motherboard. When I plug in the charger, there's no current consumption. However, the laptop works if I bypass the charger IC by applying 20V directly to the main resistor. I checked the voltages at the charger IC and found that ACOK (AC OK signal) is missing, and ACDRV (AC Drive) isn't sending voltage to the gates. I've searched for shorts but found none. I replaced the charger IC three times, but ACOK remains around 0.24V–0.35V. The MOSFETs test fine. If anyone has encountered this issue, I'd appreciate your advice.
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ACOK is an open-drain pin. When the adapter voltage is deemed to be within range by sensing the ACDET voltage to be 2v4 or higher, then the ACOK pin is floated. Because the pin is floating, there must be a mandatory pull-up resistor on this line. Perhaps it is missing.
Sometimes, the pull-up resistor is to the REGN pin. Sometimes to the 3v3 always on line. Which logic board would you have? Do you have a schematic available? The conditions are ok to enable ACDRV but be sure the DCin mosfets are not shorted.
Remove all power and measure their resistance:
source / drain
source / gate
gate / drain
Post each resistance. Repeat for the 2nd dc in mosfet. Each measurement must be hundreds of k ohms or higher else the mosfet is a suspect to be defective.
If you remove the ~4k ohm resistor that is in series with the gate pin of the 2 x DCin mosfets, what is the voltage of ACDRV without this resistor? Do not lose the resistor.
This test usually confirms if the DCin mosfets are ok or not. Suspecting that at least one is defective (as per the charger sticky article above by @piernov). -
This is the schematic, from the motherboard, and according to the ic datasheet, acdetec, acin and regn volts are enough to have the acok in a high mode (3V). And as you can see in the schematic there is no resistance and physically is not present as well. All resistance from the mosfets are above thousands. And what I understand is that acdrive cant exists if the acok is not in high mode.Comment
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Post the schematic of where ACIN is connected. The pull-up should be there.
what is the voltage to ground of CMSRC?
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I just realized that i have the same voltage in acok, acdrive and cmsrc around 0.275V. I was confusing acin with vcc. According to ic datasheet, the requirements are, acdetec above 2.4 (i got 2.76). And the vcc of 19V, even regn is 6.00V which means ok. But somehow acok is always under one volt. So if acok is not in high mode acdrive will not send the 25V to the gates.Comment
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Post #2 - Post the actual resistance measurements of the DCin mosfets for a review.Comment
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Thank you anyway brother, I found a short in the battery side, thank you.Comment
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Hi there,
I have a DK10FG-6050A2491301-MB-A03 motherboard with missing ACOK voltage. Here are the basic voltages of BQ24725A. The motherboard is dead with no signs of life.
ACN : 19.35V
ACP : 19.36V
ACDET : 2.7V
REGN : 5.916V
VCC : 19.36V
Diode mode to ground reading on ACOK rail is 0.450V on pin 1 of R6013 and 0.230V at pin 2. Replaced BQ24725A a couple of times. Still no luck.
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