LA-E921P no power

[ictc]

Hi, this board does not power on, Vin present on PQ303 drain but on its gate ACDRV_CHGR is around max 2,6V unstable. No short in most of the power rail caps and shunts, pq303 and pq304 not shorted as well. VCC on pin 28 of pu301 present, ACPRN_CHGR also present 6v stable. No Short on caps around pu301 and +19V_CHG. What could preventing the pu301 from boosting acdrv to 25V?

[mon2]

What is the voltage to ground of ACDET on the charger IC?


Each resistance check on a mosfet must be hundreds of k ohms or higher else the mosfet is most likely defective. Flux & remove PQ304 from the circuit and power up again. What is the ACDRV voltage to ground now after this mosfet is removed?

[ictc]

Apologies, I mistakenly wrote 2.6V, while the actual measured value, with and without the MOSFET, oscillates between 0.26V and 0.57V. I apologize for reporting an incorrect value. Removing the second mosfet the ACDRV rise finally to it's default value. Diode mode measurment on PR335 and PR304 gives 0,4V I think there is no short on that side, should I blame just the mosfet?Iìm also measuring 0,5V drop between source and drain in both direction on that mosfet that means is leaking in some way. I'll try to replace it and get back.

[ictc]

I replaced the MOSFET with a working one (I can now read the diode voltage drop in one direction only), but the ACDRV_CHGR voltage dropped again. I suspect that something is triggering the charger IC to stop providing that voltage whenever it receives feedback from a source unknown to me.

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance between ACP and ACN pins directly on the charger IC. We are testing the full resistance path of the current sense leg of the main power rail. Again, no power to the board during this testing.

[Sephir0th]

I replaced the MOSFET with a working one (I can now read the diode voltage drop in one direction only), but the ACDRV_CHGR voltage dropped again. I suspect that something is triggering the charger IC to stop providing that voltage whenever it receives feedback from a source unknown to me.

You should not replace parts on your own from here since this adds unknown factors this way which will make the repair even more complicated.

And if you replace something anyway, you need to state exactly what component make/model you have replaced with what component make/model.

When a Mosfet doesn't show continuity between Source and Drain or Source and Gate then it is fine in 99% of the cases. It must be something else.

Second, you were asked for ACDET voltage. Please share the voltage.

If VCC, ACDET, REGN & current sensing checks out, nothing obvious visually to notice and there is no short to GND at +19VB then it is most likely a dead charging controller.

[ictc]

Resistance between ACP and ACN pins is 0.16Ω. ACDET remains steady at 2.6V (within specifications), REGN still 6V but ACDRV drops when the second MOSFET is connected. Could this be due to a feedback or protection mechanism within the BQ24780 being triggered?

The original MOSFET was a B04N03 (BVDSS: 30V, RDSON(MAX): 4.0mΩ, ID: 75A), which was replaced by a 3N1R8 (BVDSS: 30V, RDS(ON): 1.89mΩ, ID: 165A). The replacement MOSFET has better overall specs, and I'm not concerned for this kind of application about the higher gate capacitance of the AP3N1R8MT (~3800 pF).

By the way, I initially wrongly thought the original MOSFET was leaking, (hoping for an easy and fast resolution) but after further testing, it appears to be fine and soldered back in its position. Should I blame than just the controller or should I better consider

• A short circuit or overload downstream after the second MOSFET.
• Instability in the sensing or feedback loop, especially on ACN/ACP
• ???

[mcplslg123]

Is the 19V line pulsing as measured on CLR?(both dc-in fets soldered).

[ictc]

Is the 19V line pulsing as measured on CLR?(both dc-in fets soldered).

Yes, the 19V line is pulsing. It appears just unstable, fluctuating between 5.5V and 6.5V, but using the DMM's min/max function, it shows a pulsing range from 0.168V to 6.66V.

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance to ground of the same 19v line. What is the exact measurement in ohms? No power to the board during this test.

[ictc]

Measured after the CSR, the resistance starts at approximately 20 MΩ and then decreases very slowly, resembling a capacitance discharge. It drops to 14.566 Ω before starting to increase again. If I disconnect one lead, the measurement restarts, suggesting to me that some active components might be influencing the reading.

[mon2]

It drops to 14.566 Ω

Are the units correct? ~15 ohms??

[mcplslg123]

Check VCC resistor again for exact 10 ohms. Measure voltage on both ends of this resistor.
To me it seems like VCC resistor is out of value.

[ictc]

Are the units correct? ~15 ohms??

15000 ohms.. I meant 15K, sorry for the mistake

[ictc]

The VCC resistor measures 10 ohms. The voltage is present on both side but not steady, oscillating between 14.2 and 14.4 volts

[mcplslg123]

VCC must be stable 19V for charging ic to function. Remove the 10 ohms resistor from mb and measure resistance to GND on both ends of this resistor pads.
Check the dual diode that feeds this VCC resistor

[ictc]

Removed PR312 and measured the resistance to ground. From diode PD301 side it is 2.9M and on the IC PU301 side is 1.7M. The dual diode also seems fine to me, about 0,28V of voltage drop in diode mode on both diode.

[mon2]

Is it a stable voltage if the dual diode is removed? Then the charger IC is not being powered and the raw adapter voltage will be present at Vin of the dual diode.

[ictc]

Not at all. +19V_VIN is 19.5V as it should be, but the output of the dual diode is still not stable, fluctuating sometimes between 20.7V and 22.9V. I also noticed that on the +19VB pin of the same diode, the voltage is sometimes 0V and other times randomly varies between 2.3V and 5V.

When the adapter is connected for the first time, I have approximately no +19VB and an almost steady 20.6V on +19V_VIN. After a while, +19VB starts increasing, and +19V_VIN begins to fluctuate as well. However, these two events don't appear to be directly correlated, as at the moment, I have 20.5V on the diode's output and almost 0V on +19VB.

I wonder why I'm observing random voltage spikes on pin 2 of the diode, where +19VB is not supposed to exist under this condition?

[mon2]

I wonder why I'm having +19VB kicking in on pin 2 of that diode?

If using only the adapter and yet you are observing this voltage on pin #2 of this dual diode = this diode is defective and leaking. Flux & replace this dual diode. Test again after this replacement.