[SOLVED]820-3332 no fan spin

[TheoGa]

Hello guys,

I worked the past few hours on a 3332 Logicboard and I can't get it back to life.
The one-wire circuit is working but there is no PP5V_S4, no PP5V_SUS, no PP5V_S3, no PP5V_S0 power rail. I tried to figure out why but I am stuck.
Every time I look through the schematics, I end up at the Panther-Point-Mobile (guess thats the PCH) and when I look on I end up at the power rails. It is like an infinite loop.
I hope someone can help me.

Thanks a lot!

 

[dukefawks]

History of the machine? Got green then orange light? PPBUS voltage? Are you using a REAL GENUINE APPLE 85W charger?

 

[TheoGa]

Hello,

the machine suddenly turned black while working, no signs of liquid damage.
PPBUS_G3H = 12.61V, it has a green light for 3 seconds and then it switches over to an orange light on the charger.
Yes, it is a REAL GENUINE APPLE 85W charger.

Thank you!

 

[Gurmon]

Do you have PP3V3_S5 ?

Voltage on pin 2 of R7941 ?

 

[TheoGa]

Yes, PP3V3_S5 is present and I got 3.361 Volts on pin 2 of R7941 (3.434V on pin 1)

 

[dukefawks]

SMC_ADAPTER_EN present?

I still suspect that adapter, these do not power on from anything that is not 85W.

 

[TheoGa]

Hello,
yes SMC_ADAPTER_EN is present (2.4V).
Yesterday I bought a new charger from the Apple Store and it started working again, but suddenly the machine died again.

After the machine died, I heard a ticking noise when I attached the charger. I then replaced U7201 which stopped the ticking noise but the machine wont turn on.

My power rails:
- PPDCIN_G3H = 16.69V
- G3H & 3V42 present

- PP5V_S5 = 0V!!!
- PP5V_S4 = 1.4V
- PP5V_S3 = 0V!!!
- PP5V_S0 = 0V!!!

- PP3V3_S4 = 0V
- PP3V3_S5 = 1.56V
- PP3V3_S3 = 0V
- PP3V3_S0 = 0V

U7201 measurements:
- VIN = 12.61V
- EN2 = 3.41V
- EN1 = 0V

now when I look up where EN1 comes from, I get to U7970 which should theoretically be enabled when PP3V3_S5_PWRCTL
is present. But the problem is that PP3V3_S5_PWRCTL comes from U7201 which depends on PP3V3_S5_PWRCTL. This is a infinite loop. What can I do?

U7970 measurements:
- Pin 6 (Enable) = 1.5V

Thank you a lot!!!

 

[dukefawks]

PP5V_S5 is a simple LDO from U7201. Check enable at pin 12 and check for short on PP5V_S5. PPBUS still present and 12.6v?

 

[TheoGa]

Hello,

I get 3.41V at pin 12 of U7201

PP5V_S5 is 1.4V at C7205 (very very slowly increasing voltage - from 0V to 1.4 approx. 30 sec.)

Yes PPBUS_G3H is 12.6V

 

[dukefawks]

Well 5V_S5 should be present then if there is no short on that bus. So either dead U7201 or bad traces/soldering. VIN pin 23 is also a common suspect.

 

[TheoGa]

I just replaced U7201 for testing purposes and I think now I have a fully working chip but the ticking noise is back.
I now have clean 5V on 5V_S5 but when I hear a tick on the logicboard, the voltage on 5V_S5 drops to 3V for a few milliseconds.
I think thats probably the issue why nothing is working but where does this ticking come from? SMC?

And I have 12V on pin 23 (VIN) of U7201

 

[Alan.L]

Ticking is probably from a coil. I bet you didnt eliminate the inital ticking noise.....then again unreliable rail can also cause coil making ticking noose.

 

[TheoGa]

I also guessed the noise came from a coil but I can't figure out which

what do you mean with "unreliable rail can also cause coil making ticking noose"?

 

[Alan.L]

you can start by check all the coils used in S4/S5 state. like L6995. you dont need to check coils use for screen, keyboard backlight and thunderbolt.

 

[TheoGa]

Ok, thank you. Do you mean I should check them for a short inside the coil or infinite resistance or... ?

 

[dukefawks]

Check for short to GND on L7220 or L7260.

 

[TheoGa]

I checked all coils and I couldn't find a single short.
The wired thing I found is that when I removed C9823, C9848 and C9849 the ticking stopped except one tick at the beginning. I now replaced these three parts but nothing changed. noise still there.
I am kind of clueless..

 

[dukefawks]

Is the machine power cycling? It sounds like it is running into a short somewhere. Check all rails for shorts including all S3 and S0 rails.
Was this liquid damage?

 

[Alan.L]

by this time, i would start injecting voltages into each rail to see when the noise is coming from and check if anything gets hot..

 

[TheoGa]

Hello,

Thank you guys, I now fixed my ticking issue! it was some come kind of corrosion or some nasty stuff near U8900 which caused a short. (The board was officially not liquid damaged)

Now the fan spins but while checking all the coils I realized that I have a short on L7510, L7520, L7530, L7550, L7560, L8930, L8960 (the coils under the black tape).
Basically the CPU get very hot very fast and when I go over the circuits for Phase 1,2,3 and AXG Phase 1,2 I see a short to ground on the CPUIMVP_PHASEXX rails. Is there a way to check the all transistors (Q7515, Q7551,...) without desoldering them? Or do you think they could be the problem?