820-00165 No Power

brunomotter

Member
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?
 

brunomotter

Member
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.
 

Askaleto

Member
Brunomotter,

had recently an issue with U8030, which is also the same load switch. Remove U8020 and inspect closely in what state are the pins on the board. It is possible that pad for enable signal is damaged and that EN voltage is not really getting to the switch. Both Vin and Vout have double pads/pins but EN is only one pad and very sensitive. It is possible that EN signal doesn't have a real contact to the witch ball, since it is BGA chip.
If pad on the board is even slightly damaged, then it is possible that there is no contact between EN ball on the TPS chip and actual pad on the motherboard.

There is also one more thing you can check. When measuring voltage, place red probe on the casing of the U8020 switch and check wheter there is voltage on the case to the ground.
 
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brunomotter

Member
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

Member
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

Member
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
 

brunomotter

Member
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.
 

brunomotter

Member
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.
 
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