Lenovo Legion Y520-15IKBM - No power besides the main rail

[Fronczek]

Hello people,
I've got this laptop not working for repairs, and as you can see something was done to it as you can see in the coils PL58XX (which I for some reason cannot find in the schematics...) The first FET (PQ201) was not an original part and a questionable one at that and the second one (PQ202) was shorted. Both are N-channel. Ordered replacements for them and replaced them after arrival. Now I have encountered another problem: there is no power at the second FET. By following the thread linked I got to the injection part. Applied 0.8V at 1.5A, but couldn't feel anything getting hot, so upped it to 1V at 2.5A and to my relief the PCH nor the CPU is getting hot. What is though, is the area near the first FET. I don't have a thermal camera, so further troubleshooting is an issue. I suspected that one of the caps gone bad, just in case did measurements that I put in the photos, but it's conflicting with what seems most likely the first FET getting hot, but I feel heat in the general area of it. Help will be much appreciated! I'm attaching a schematic for this board, and a few photos.

Measurements:
Main rail (VIN) is 20.6V
PF101 has continuity, so it's not the fuse
None of these 5 caps have the same voltage on both terminals
PQ201:
S-D - 20.2V, 2.8MΩ
S-G - 0V, OL
D-G - 20V, OL
PQ202:
S-D - 0V, 3.5MΩ
S-G - 0V, 3.8MΩ
D-G - 0V, 5.2MΩ
ACDET is 2.8V
ACOK is 0V

LINK to schematic -> https://www.badcaps.net/forum/troubl...45#post1352445

[mon2]

Locate the battery charger IC -> review the VCC (power rail) of the charger IC. Is it being powered? Confirm the voltage to ground of the REGN pin on the charger IC. It should be ~6 volts.

If the charger IC is not being powered, then the gate pins of the DCin mosfets will not be available to enable this power path.

[Fronczek]

Yep, REGN is at 6V and the VCC's being fed 20.3V

[mon2]

Measure the voltage of the ACDRV pin on the charger ic. It should be ~25v if all is well. If not, remove the ~4K ohm resistor in series with this line and test the acdrv pin again.

[Fronczek]

ACDRV is gone even without the resistor in question, also why 25V?

[mon2]

N-channel mosfets require gate pin voltage to be higher than the source / drain voltage being passed to enable.

gate voltage = adapter input voltage + REGN voltage = 19 volts + 6 volts = 25 volts.

Best to carefully (!!) measure the voltage to ground of each pin on the charger ic with the power adapter attached. Post each measurement.

[Fronczek]

Weirdest thing just happened - plugged in the laptop and seen sparks from a capacitor (PC216). It blew up, so I replaced it for a smaller one but with a higher voltage rating and ACDRV is back???????????????
#1 (ACN) - 19.95V
#2 (ACP) - 19.95V
#4 (ACDRV) - 26.45V
#5 (ACOK) - 3.3V
#6 (ACDET) - 2.8V
#11 (SDA) - 3.3V
#12 (SCL) - 3.3V
#15 (BATPRES#) - 3.3V
#16 (TB_STAT#) - 1.35V
#17 (BATSRC) - 220mV
#18 (BATDRV) - 250mV
#19-20 (SRN, SRP) - 220mV
#21 (ILIM) - 1.35V
#24 (REGN) - 6V
#25 (BTST) - 5.7V
#26, 27 (HIDRV, PHASE) - 220mV
#28 (VCC) - 20.3V

The rest have 0V

Let me add that the battery is not plugged in as of testing.

[Fronczek]

Sorry my post is in sort of an "Unapproved" limbo

[SMDFlea]

Sorry,it was due to the forums spam filter

[Fronczek]

Weirdest thing just happened - plugged in the laptop and saw sparks from a capacitor (PC216). It blew up, so I replaced it for a smaller one but with a higher voltage rating and ACDRV is back??

[mon2]

The voltage list looks good. Check the voltage to ground at each inductor (usually are grey in color). Each inductor is linked to a power rail. Measure each to check if that rail is working or not. Or test the board again.

[Fronczek]

The laptop is indeed booting, although it seems to be stuck in boot/bios, it doesn't output to HDMI (the matrix is missing at the moment). The charger plugged LED seems to be missing as well

[mon2]

Do you have video on the lcd display?

[Fronczek]

Got the laptop for repairs without one, and I don't have a 30 pin lcd at the moment. I could order one right now.

[mon2]

It is ok to test with HDMI. No video with HDMI? Does the keyboard caps key led toggle?

[Fronczek]

Yep, no video at all. The fans are working at the max rpm (I think) and the components are getting hot, and yes the caps led toggles.

[ktmmotocross]

Guys i have same problem . Always with this bloody 780S. anybody know what is main trouble with them?

i have looks like all things that needs to be have/voltages/, but after half a second ic put power down. i see spiked ACDRV, ACOK, but only for a halfsecond. mosfets are ok, i changed ic, ADAPTER_ID is 1Kohm to GND so with 135W adapter is ok

when i jump first mosfet laptop works

[mon2]

Ideally, share the measurements of the voltage to ground of each pin on the 780S.

At the very least share,

VCC ; is the charger IC being powered?
REGN ; must be ~6 volts
ACIN ; current sense voltage of the main power rail
ACIP
ACDET ; is the power adapter threshold being met to enable the DCin mosfets?

If the current sense resistor path is not complete or out of spec, the DCin mosfets will be turned off.

[ktmmotocross]

Ideally, share the measurements of the voltage to ground of each pin on the 780S.

At the very least share,

VCC ; is the charger IC being powered?
REGN ; must be ~6 volts
ACIN ; current sense voltage of the main power rail
ACIP
ACDET ; is the power adapter threshold being met to enable the DCin mosfets?

If the current sense resistor path is not complete or out of spec, the DCin mosfets will be turned off.

VCC ; 20V
CMSRC - 0V
REGN 6V
BS - 5.7V
IADP - 0V
ACDET - 2.8V
VDD - 6V
ACDRV - 0V

All missing voltages is normal for a half second and than goes down

[mon2]

Remove all power. Meter in resistance mode.

1) measure the resistance between pins 1 & 2 but do so directly at the charger IC.

2) measure the resistance to ground of pin # 2 of this charger IC.

Post both measurements.

[mcplslg123]

ACDRV will only rise when CMSRC is present and ACOK is pulled high. Seems like overcurrent shutdown by charging IC.