Latitude E7250 3.3v/5v IC overheating

[pingaroon]

Hi folks,

I have a Dell E7250 board which has the main power rail up, but no 3.3 to the power button because the PU100 chip (TPS51285) is not working. With the charger attached, it starts to heat up until extremely hot.

None of the surrounding capacitors are short.

I have replaced the chip with a known good one, but that one too burns hot ??

I have 2 other good boards - on the good boards, pins 6 and 20 (the enable pins) are shorted to ground when the board is off. I don't fully understand why, but that seems to be the normal behaviour.

On my bad board, none of pins are shorted to ground (but the central pad is correctly grounded).

I then changed the KBC chip UE2 (MEC5085), but the problem remains the same.

The heat must indicate a short somewhere. How can I determine if the problem is with the TPS51285 chip or elsewhere causing it to heat up?

Any help gratefully appreciated.

[master7]

Re: Latitude E7250 3.3v/5v IC overheating

Hello, if you replaced the pu100 and continued to heat up, it is necessary to check if some of the coils PL101 and PL102 are shorted. Check their resistance in relation to the GND of the board and the voltage of pins 3, 7 and 13.

[ktmmotocross]

Re: Latitude E7250 3.3v/5v IC overheating

mostly sio or audio ic problem if u dont have shorted alw rails

[pingaroon]

Re: Latitude E7250 3.3v/5v IC overheating

Hi,
Resistance from PL101 is 11.4 kΩ, and PL102 22.4kΩ
Pin 3 is 1.15V (VREG3)
Pins 7 (VREG5) and 13 (PGOOD) are 0 volts

With the chip at PU100 fully removed, I found that the output of pin 3 linked to PD3 which was burning hot when I injected 3.3v at the capacitor on the output of pin 3. the short was so strong that the best I could get was generalised heat over the board, so couldn't pinpoint a specific component. The cpu area was slightly warmer, so it could have been that.

[Sametbey]

Re: Latitude E7250 3.3v/5v IC overheating

examine the similar scheme. first, 12 pin e 19v should come. 3 and 5 pins should be 3v and 5v. 6 and 20 pins when the enable signal comes out of the coils voltages. Make a short circuit cotrol on pins 3 and 13.

[ktmmotocross]

Re: Latitude E7250 3.3v/5v IC overheating

remove pr103 and pd3 to better locate short

[pingaroon]

Re: Latitude E7250 3.3v/5v IC overheating

Hi folks, Even with PD3 removed, when I inject at that point, the best I can bet is generic heat, so I think this one is toast Thanks for your help