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Lenovo Flex 5 LC56-14T blown after connecting USBc charger - 19V 0.04A

it-solve

it-solve

Member
Hi Guys, I know this is an Apple sub, but not sure if you can help me with this one too. I got a schematic and boardview for a close model. location of the parts on the board are a bit shuffled, but schematic ics seem to match. Here link to the Schematic and Boardview - Lenovo FLEX 5-14ALC05 – LC56-14A SVT

I got two of these, both have been connected to the same (doggy?) usbc, which blew them one by one.
I have detected a short on the 5V line and traced it down to U7204 (which was glowing at 1V over 5V line). Replaced it, and the short is gone. However, I cannot get 3.3 and 5V lines to fire up.

PU4501 is heating up slightly and was dropping the DCBATOUT voltage from 19 to 9 V. After replacement, it now stays at 19V with no drop.
Now still slight heat signature on PU4501 bench shows 19V/0.04A



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1684657599516.png

PU4501/4551, same voltages
P1 - 4.5V
P2 - 19V
P6 - 0V
P9 - 0V
P11 - 4.7V
P12 - 0V
P13 - 0V
P14 - 0V
P15 - 5V / 2.7V
P17 - 5V
 

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it-solve

it-solve

Member
Yes TPS51393 for sure, but I had one from the donor board, which is the other failed board. So how reliable not sure. And I don't have this chip.

I would have thought that 5V and 3.,3 fire separately. Could missing both voltages at the same time would be still faulty TPS51395/3

1684710780702.png

How can you spot which component is it without an accurate boardview? Seems to be a bigger size one? 0603?

Only one in that package size seems to be missing on the left of D2502.
1684713362647.png

3D3V_RTC_AUX - 3.3V
3D3V_AUX - 2.7V


Removed the Diode (if that is the one) and I get 2.70 on 3V3V_AUX_S5 and lost 3D3_RTC_AUX which was 3.3V with the diode.
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
Then the problem doesn't come from RTC area; put back D2502.

R2425 not used probably; free pads next to D2502.

If you change PU4501 and still 2.7V there, then bad KBC.
 
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