3115-B, dim green light on magsafe + DCIN rails pumping?

[Hardwood T/S]

Dim green light on magsafe, somebody had apparently tried to repair this board previously... both ADAPTER_SENSE and PP18V5_DCIN_FUSE jump every second, SENSE between ~3.9v to ~4.1v and FUSE between ~17.1v to ~16v. No shorts on any of those lines, and PPBUS_G3H descends constantly from around ~200mv but jumps every few seconds to around ~350mv and straight back down to continue descending, while 3V42 is constant at 17mv, no jumps. Have to run, but any symptoms sound familiar to you guys? Will test any more rails I need to once I get back, may be tomorrow tho.

 

[JohnB8812]

Known good DC in board and 85 watt magsafe 1? Resistance to ground on PP3v42?

 

[Hardwood T/S]

Yes charger is known good, I've been using a 60w since it's a 13" board, but 85w returns same results. Tried multiple DC-in boards, PP3v42 has .310v drop in diode mode to ground, 1.655kohms in resistance.

 

[2informaticos]

Possibly leakage on the input stage.
Original charger detects it and gets blocked.
First check for short at CHGR_ACIN.
Also be sure both R7010/11 are OK.

Post exact value for R7080/81 and R7085/86; measured onboard, ohm scale.
Also post diode mode to ground at R7020, L6995 and C6990.

 

[Hardwood T/S]

While looking at R7080/81 I discovered R6905/R6990 were completely missing from the board maybe the guy before was using this board for parts, not sure. Either way, after replacing I now have stable DCIN rails, 3V42 and PPBUS_G3H are 3.44v and 12.56v respectively. The resistors you mentioned all returned normal values, plus current sensing is fine as well.
ONEWIRE and ADAPTER_SENSE are ~1.49v. No shorts on those lines. U6900/01 look fine, should try replacing anyway? Already replaced ISL earlier no change.

 

[2informaticos]

Post all voltages for U6900/01.

 

[Hardwood T/S]

U6900
(1)SMC_BC_ACOK_VCC 2.00v
(4)SYS_ONEWIRE 2.00v
(5)ADAPTER_SENSE 2.00v

U6901
(1,2)SMC_BC_ACOK 3.27v
(4)SMC_BC_ACOK_VCC 2.00v
(5)PP3V42_G3H 3.44v

Voltage went from 1.47v to 2.00v on the ONEWIRE lines since last time but still low.

 

[2informaticos]

"SMC_BC_ACOK_VCC 2.00v"
Replace U6901.

 

[Hardwood T/S]

Replaced it, works now thanks a bunch. Why does ACOK_VCC being 2.00v conclude U6901 being bad and not U6900?

 

[2informaticos]

U6901 generates that voltage, from 3V42; enabled by SMC_BC_ACOK.
If U6900 sinks too much current, it should drop more...