820-2915-a Spontaneous Shutdown, No Startup

[JustAnotherGuy]

The pulsing inductors measured above continue pulsing when I ground the SMC_ONOFF. However, the pulsing frequency approximately doubles while SMC_ONOFF is grounded, and afterwards when I disconnect the SMC_ONOFF, it goes back to its previous frequency.

 

[2informaticos]

Don't ground SMC_ONOFF_L, trigger it; like when pressing power button, less than 1s.
Use R5015/16 pads, instead of power button; when work with the board alone on the desk.
You must check signals and voltages reaction at the same moment.

In fact, solder an wire on SMC_ONOFF_L and touch any metal plate, simulating power button.

 

[JustAnotherGuy]

Understood. Please see the attached images for what I mean by grounding. The blue line is the scope of the "trigger". The pulsing is still there.

 

[2informaticos]

When using o-scope, check for DC pulse at output pin of the coil; where the filter cap is connected.

 

[JustAnotherGuy]

The plots were taken with probe on pin 2 of inductors L7260 and L7770.

 

[2informaticos]

Very strange pulses.
If you hold down (to ground) SMC_ONOFF_L for 5s, still get pulse on these coils?

 

[JustAnotherGuy]

yep still pulses, as shown in attached images

 

[2informaticos]

Keep SMC_ONOFF_L down more time, it should turn off the board.
Only 3V3_S5 must remain present after and no pulse on other coils.

 

[JustAnotherGuy]

Not sure what happened but the behavior changed. So this is the process:

Power cycle
L7260_1_1
Disconnect SMC_ONOFF_L
L7260_1_2
Power cycle
L7260_2

So it looks like the behavior changed after the first long press of SMC_ONOFF_L. Now it seems like grounding SMC_ONOFF_L causes the PP3V3_S5 to go to 2.5V as opposed to pulsing. Then after grounding is removed, the voltage stays constant at 0.5V. The pulsing does not return until the board is power cycled again.

After power cycling, the pulsing starts again. During that time, the other coils that show pulsing (L7770 for example) continue to pulse. However, after the pulsing stops (after holding SMC_ONOFF_L for more than 1 second, as stated above), those lines go to 0V.

Also, not shown here, after power cycle, and while it is pulsing, when I do a short "press" of SMC_ONOFF_L, grounding for maybe 1 second? the voltage jumps to ~2.4, and then when ungrounded it stays at 0.5V. However, if I just "tap" SMC_ONOFF_L, grounding maybe 0.1seconds?, the voltage jumps to ~2.4, but when ungrounded goes back to pulsing.

 

[2informaticos]

Once Magsafe is connected, 3V3_S5 must get stable (C7290), no matters board is on or off.
Confirm your actual case.

 

[JustAnotherGuy]

voltage pulses at C7290, same as L7260, once MagSafe is connected. once SMC_ONOFF_L is grounded for 1-2 seconds and then ungrounded, it stays stable at 0.75V, the same as L7260 from above.

 

[2informaticos]

I think in early post you've said to have steady 3V3_S5 voltage.
Check now PPBUS_G3H, 3V42_G3H, SMC RESET_L and SMC_PM_G2_EN.

 

[JustAnotherGuy]

PPBUS_G3H -12.48V
3V42_G3H - 3.48V
SMC_RESET_L - 3.48

SMC_PM_G2_EN:

• after MagSafe connection: pulsing 0 - 3.5V
• after holding SMC_ONOFF_L for 3s: stable at 3.5V

All behavior above, with the exception of SMC_PM_G2_EN after holding SMC_ONOFF_L, is the exact same as it was initially.

PP3V3_S5 has never been stable at 3.3V. Once MagSafe is connected it pulses from 0 - 3.5V. The only time it is stable is after the SMC_ONOFF_L long hold to ground, after which it settles at 0.75V.

 

[2informaticos]

You cannot get 3V3_S5 untill SMC_PM_G2_EN is stable.
Remove R7940 and run a wire from 3V42_G3H to C7942.
Check if 3V3_S5 gets steady voltage then.

 

[JustAnotherGuy]

removed R7940, soldered a wire from pin 2 of where R7940 used to be (PP3V3_S5_EN) and also happens to be pin 1 of C7942, to pin 1 of R7941 (PP3V42_G3H).

PP3V3_S5 at C9487 pulsing 0 - 3.5V as usual.

 

[2informaticos]

Post basic voltages of U7201 now; pins 23, 12, 13, 22, 29, 21.

 

[JustAnotherGuy]

Pulsing behavior on some pins.

 

[2informaticos]

I asked about DC voltages!
PLEASE, hide the o-scope somewhere...

 

[JustAnotherGuy]

The voltage is on the left axis of each image.
Pin 12 - Pulse 0-3.5V
Pin 13 - Pulse 0-2V
Pin 21 - 3.5V
Pin 22 - 3.35V
Pin 23 - 12.25 - 12.75V ... weird interference, matches pulse frequency
Pin 29 - Pulse 0.9 - 5V

 

[2informaticos]

I understand SMC_PM_G2_EN is still pulsing.
There should be a problem with SMC, or some of its sensors.

Check exact ohm resistance between pins 17/18 and 27/28 of U7000.
Remove F7040/41 and check the voltage at C7040.