820-00165 No Power

[brunomotter]

Hello. Got an 820-00165 board here with no power. It had little corrosion around U8020, so I removed the IC, cleaned everything and replaced the IC. Still no power. I get a little low voltage on R8020. It should be 3.42V but I get only 2.9~3V. Replaced the IC a lot of times already and same result. If I inject 3.4V on R8020 pads the board starts, but obviously this isn't a solution. Already lifted all caps on the line but same result. Any ideas on where to look?

 

[2informaticos]

Post P3V3SUS_EN voltage.
U8020 gets correct 3V3_S5?

 

[brunomotter]

P3V3SUS_EN - 3.3V
yes, it gets steady 3V3_S5 but does not output correct voltage. That's why I thought U8020 was bad initially, forgot to mention.

 

[2informaticos]

Looks like bad U8020.
Post diode mode to ground at 3V3_SUS.

 

[brunomotter]

Diode Mode on 3V3_SUS - 0.392
Already replaced about 10 times U8020

 

[brunomotter]

Thanks for answering and trying to help. Removed U8020 and enable signal is steady 3.3V on the pad, so no problem there. I tried jumping 3.3V directly to R8020 and when doing this 3.3V line goes to 3V as when with U8020 in place. Something is dragging down the line and I cannot figure out what is.

 

[brunomotter]

Replaced once again U8020 and for precaution U8030, same result!

 

[2informaticos]

Did you test the board alone on the desk?
Disconnect anything, keep only 5 pins power cable.

 

[brunomotter]

Yes, that's how it is right now. Same thing. Tested with known good magsafe board and cable and with known good magsafe board with no interconnect cable. Same results.

 

[brunomotter]

I don't have any other ideas... Already poked around everywhere on this board. Any other suggestions?

 

[2informaticos]

So 3V3_S5 drops when solder U8020?
Did you solder it in correct way?

 

[brunomotter]

Yes, properly soldered, I removed from identical donor board and soldered in same orientation.

 

[brunomotter]

And it's not PP3V3_S5 that gets dragged down. It's just not outputting correct voltage. PP3V3_SUS is low. Should be 3.3 and is 3.08V

 

[2informaticos]

Does the board start if you bypass U8020?
Just for test...

 

[brunomotter]

I tried bypassing, jumping 3v3 directly. The board starts for some times then stops. When I jump 3v3_S5 directly to the output it drags 3v3_S5 down to 3.08V. If I solder the MOSFET the 3V3_S5 is fine but the output stays on 3.08V.

 

[2informaticos]

Doesn't try to start with 3V at 3V3_SUS?

 

[brunomotter]

If I inject 3.3V from bench PSU the board starts, but if I make a jumper from any 3.3V line from the board it will drag that line down and intermittently start.

 

[brunomotter]

Looks like a cap leaking voltage, but I lifted literally every single cap on the line and problem was not solved.