Hi,
This machine was entrusted to me with a note saying "doesn't work, no lights, probably motherboard".
Indeed, after plugging in the charger, nothing was happening and the battery wouldn't charge. Obviously an issue with the charging circuit.
No voltage on the B+ line (measured on the 10mOhm current sense resistor of charging circuit), but the 19V was present after the DC in connector, meaning the DC-in MOSFETs weren't passing through the current.
First I thought the charger IC (bq24735) was dead because I had 0.8V on various pins (CMSRC, ACDRV, ACOK if I remember fine), even though I had 19V on VCC, 5.8V on REGN and 2.8V on ACDET. I replaced it with a bq24740 (which should've at least shown a different behaviour) but nothing changed so I was wrong.
Indeed, the second DC-in MOSFET (towards the system side) was completely shorted (gate/source/drain), so that's why I had the same voltage on all those pins.
Replaced it with what I had laying around, a 4921N, too large to fit properly but at least it works now, turns on and charges the battery.
As always, I forgot to take pictures.
This machine was entrusted to me with a note saying "doesn't work, no lights, probably motherboard".
Indeed, after plugging in the charger, nothing was happening and the battery wouldn't charge. Obviously an issue with the charging circuit.
No voltage on the B+ line (measured on the 10mOhm current sense resistor of charging circuit), but the 19V was present after the DC in connector, meaning the DC-in MOSFETs weren't passing through the current.
First I thought the charger IC (bq24735) was dead because I had 0.8V on various pins (CMSRC, ACDRV, ACOK if I remember fine), even though I had 19V on VCC, 5.8V on REGN and 2.8V on ACDET. I replaced it with a bq24740 (which should've at least shown a different behaviour) but nothing changed so I was wrong.
Indeed, the second DC-in MOSFET (towards the system side) was completely shorted (gate/source/drain), so that's why I had the same voltage on all those pins.
Replaced it with what I had laying around, a 4921N, too large to fit properly but at least it works now, turns on and charges the battery.
As always, I forgot to take pictures.
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