FH51M LA-J871P charging issues

[reparetech]

Hi, I have this Acer Nitro FH51M LA-J871P that intially came in because it did not turn on at all.

Short detected on +19VB which turned out to be PC1105 shorting +19VB_1VALW. Capacitor removed and replaced.

Now, the computer turns on (on charger, and on battery), but it does not charge and the charging light flashes after about a minute.

What has been done:
- PUB1 has been replaced, didn't change anything.
- Changed battery, didn't work
- Changed charger, didn't work
- Updated BIOS (When it was updating, the charging light stayed on, but started flashing afterwards, not sure it if actually charged anything, as the battery still said 26% in Windows before/after)

I verified that the RTC battery is at 3V and +RTCVCC is 2.92V

Measuring PJP201: pin 1-2: 0V, pin 3: 3.15V, pin 4: 3.18V, pin 5: 0.150V, pin 6: 0V, pin 7-8: 15.920V,

Measuring PQB2, pin 1-3: 15.920V, pin 4: 15.822V, pin 5 measures 19.158V.


If anyone had any input on what to look for next, that would be great !

Thank you !

[MOD EDIT]
Link to Schematic + Boardview https://www.badcaps.net/forum/showthread.php?t=106787

Reminder: rules and organization of this section - https://www.badcaps.net/forum/showthread.php?t=117483
.

[mon2]

Re: FH51M LA-J871P charging issues

Hi.

1) You have posted the schematics in this forum instead of the dedicated schematic forum. @SMDFlea may force you into a labour camp to have you desolder plugged vias of a multilayer PCB with a 15W soldering iron as a form of a punishment.

2) Be sure the battery is a known good battery. Does not hurt to order one from Amazon for a quick confirmation. Can be returned if not required.

3) The charger IC should be reviewed. Carefully measure the voltage to ground of pins 19 / 20 (SRN / SRP) on PUB1 with the power adapter and also the battery connected. In general, a good idea to measure (carefully) the voltage to ground of each pin on this charger IC for a review. Post each measurement.

[reparetech]

Re: FH51M LA-J871P charging issues

Hi.

1) You have posted the schematics in this forum instead of the dedicated schematic forum. @SMDFlea may force you into a labour camp to have you desolder plugged vias of a multilayer PCB with a 15W soldering iron as a form of a punishment.

2) Be sure the battery is a known good battery. Does not hurt to order one from Amazon for a quick confirmation. Can be returned if not required.

3) The charger IC should be reviewed. Carefully measure the voltage to ground of pins 19 / 20 (SRN / SRP) on PUB1 with the power adapter and also the battery connected. In general, a good idea to measure (carefully) the voltage to ground of each pin on this charger IC for a review. Post each measurement.

1. Sorry, I posted the schematics to help people who would want to dianose the issue.

2. I have actually tried two batteries. Started with a non-original one and then ordered an original Acer battery. Same issue.

3. Pin 19: 15.938V, pin 20: 15.938V Also measured 20.1 ohms between pin 19 and 20.

Thank you very much for your help.

[mon2]

Re: FH51M LA-J871P charging issues

These measurements look fine.

Best to measure the voltage of each pin on this charger IC to better understand what the component is or is not doing.

For example, is the charger IC being powered?

ACOK?

ACDET?

Voltage to ground of EC_SMB_DA1? EC_SMB_CK1?

[reparetech]

Re: FH51M LA-J871P charging issues

these measurements look fine.

Best to measure the voltage of each pin on this charger ic to better understand what the component is or is not doing.

For example, is the charger ic being powered?

Acok?

Acdet?

Voltage to ground of ec_smb_da1? ec_smb_ck1?

1: 18.960v
2: 19.157v
3: 19.729v
4: 19.727v
5: 3.295v (acok)
6: 2.593v (acdet)
7: 1.903v
8: 0v
9: 0v
10: 0v
11: 3.180v
12: 3.198v
13: 0v
14: 0v
15: 0.151v
16: 0.107v
17: 15.927v
18: 15.913v
19: 15.926v
20: 15.926v
21: 1.045v
22: 0v
23: 0v
24: 6.042v
25: 15.646v
26: 15.780v
27: 15.927v
28: 19.390v

ec_smb_da1: 3.190v
ec_smb_ck1: 3.201v

I don't know much about how this IC works, so I might be wrong, but the only thing that looks weird to me is how BATDRV is not 6V above BATSRC to turn on the FET.

[mcplslg123]

Re: FH51M LA-J871P charging issues

I think you mean ACDRV not working. Theoritically,ACDRV should work when VCC+CMSRC is present and ACOK is pulled high. Since all the conditions are met,it should be 25V approx.

I doubt your readings on pin1-2 of charging IC-it should be practically same(may be PRB3 damaged).PQB3 and/orPQB4 is very likely shorted /leaky.

[reparetech]

Re: FH51M LA-J871P charging issues

I think you mean ACDRV not working. Theoritically,ACDRV should work when VCC+CMSRC is present and ACOK is pulled high. Since all the conditions are met,it should be 25V approx.

I doubt your readings on pin1-2 of charging IC-it should be practically same(may be PRB3 damaged).PQB3 and/orPQB4 is very likely shorted /leaky.

Sorry, I must have had a finger on the probe, pin 1 actually measures 19.069V. With that measurement, iadp (pin 7) seems to make a lot more sense.

While battery and charger are plugged in:

PQB3:
Pin 1-3: 19.739V
Pin 4: 19.733V
Pin 5: 19.740V

PQB4:
Pin 1-3: 19.739V
Pin 4: 19.733V
Pin 5: 19.158V-19.161V

PRB3:
Pin 1-2: 19.158V-19.161V
Pin 3-4: 19.158V-19.161V

PRB3 fluctuates constantly

Is it safe to assume +19V_P2 (pin 5 of PQB4) should be higher and that I should try replacing PQB4 ?

Thank you very much for your help

[mon2]

Re: FH51M LA-J871P charging issues

Pin # 4 = GATE voltage to ground of the DCin mosfets (PQB3 & PQB4) are in question.

To enable these N-channel mosfets the GATE voltage should be higher than the voltage being passed between source & drain pins.

So gate voltage should be = adapter voltage + REGN voltage (~6 volts) = 19v + 6 volts = ~25 volts to ENABLE each N-channel mosfet.

Since the gate voltage is NOT this boosted voltage yet the voltage is passing through, the mosfets are of concern. As per the sticky above by @Piernov, usually the bad boy is @ PQB4 (2nd DCin mosfet).

Remove all power. Meter in resistance mode.

Measure the resistance across the mosfet pins to check if they are leaky.

Measure:

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


Post each measurement for PQB3; PQB4. If you see 'OL' on your meter, then switch to a higher meter scale (unless it is auto select). Post also the units of the scale (ie. K ohms, etc.).

A low resistance = mosfet is defective.

[reparetech]

Re: FH51M LA-J871P charging issues

Pin # 4 = GATE voltage to ground of the DCin mosfets (PQB3 & PQB4) are in question.

To enable these N-channel mosfets the GATE voltage should be higher than the voltage being passed between source & drain pins.

So gate voltage should be = adapter voltage + REGN voltage (~6 volts) = 19v + 6 volts = ~25 volts to ENABLE each N-channel mosfet.

Since the gate voltage is NOT this boosted voltage yet the voltage is passing through, the mosfets are of concern. As per the sticky above by @Piernov, usually the bad boy is @ PQB4 (2nd DCin mosfet).

Remove all power. Meter in resistance mode.

Measure the resistance across the mosfet pins to check if they are leaky.

Measure:

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


Post each measurement for PQB3; PQB4. If you see 'OL' on your meter, then switch to a higher meter scale (unless it is auto select). Post also the units of the scale (ie. K ohms, etc.).

A low resistance = mosfet is defective.

Thanks. The sticky is exactly what I read, I unfortunately missed the part about the gate voltage though.

PQB3:

S-D: 0.20 ohm
S-G: 2.08 Kohm
G-D: 2.90 Kohm

PQB4:

S-D: 0.280Mohm and growing (39.32 Kohm measured in reverse)
S-G: 2.09 Kohm
G-D: 0.260 Mohm

Removed PQB4, PQB3 short between source and drain is still present.

Thermal camera (before the mosfet was removed) showed no shorted caps anywhere, so I can safely assume PQB3 is bad ?

[mon2]

Re: FH51M LA-J871P charging issues

Yes, remove PQB3 as well and check if the short is gone or not.

[reparetech]

Re: FH51M LA-J871P charging issues

Yes, remove PQB3 as well and check if the short is gone or not.

Thank you @mon2 and @mcplslg123. PQB3 is indeed shorted as tested out of the board.

I clearly don't know enough about these types of charging circuits, I never realized the computer could still work even with a shorted mosfet in these HPB designs. I have learned a ton from you.

I ordered a CSD17573Q5B as that's what I could find quickly without ordering from China. Hopefully, it will work.

Thanks again!