820-4924 Shorted U7501, Green Light No Power

[computercaverva]

Got a board in that has no signs of physical or liquid damage. I get proper 12.58V on PPBUS. After plugged into the MagSafe the TPS IC U7501 gets extremely hot. I replaced the U7501 as well as the 2 MOSFETs and the shorts on the 3v3 rails was removed. However even after replacing those components after plugging the board into power again U7501 gets burning hot again. I have visually checked the capacitors on the rails and even removed the 3v3 coil to isolate the issue and am still at a loss.

 

[TCRScircuit]

Short on PP3v3 and PP5v rails?

 

[dukefawks]

U7501 will only get hot if one of the LDOs has a short, check VREG3, VREG5, VREF2 for short to GND.

 

[computercaverva]

PP5V_S5 is shorted to ground, as is 3v3_S5. VREG3 and VREF2 are not shorted to ground. Is there a funny name for the VREG5 rail?

Diode mode on VREG3: 0.568 and VREF2: 0.541.

Should I inject voltage on the 5V and 3V3 S5 rails or will that damage sensitive 3V3 components?

 

[dukefawks]

There are so few parts on this rail you can find the short easily. C7505 would be suspect number 1.

 

[computercaverva]

Got the PP5V_S5 short resolved last night it was C7505, 3V3 is still sorted to ground and after replacing U7501 a second time (after resolving the C7505 short) U8000 is getting hot and I have a 3 Ohm resistance to ground of PP3V3_S5.

 

[dukefawks]

You can only hope the short is caused by U8000, if not then this board probably got fried pretty good.

 

[computercaverva]

Yeah I've tried pulling U8000 and the short is still present. I'm guessing the client was using a Chinese POS charger and killed this thing. Will I have any luck with injecting current? As of late all I ever seem to get are hot lead wires!

 

[larossmann]

You can inject current it's just 99% chance that what gets hot is the CPU. I would go for it and start with 1v and see what happens.