820-476-A no fan spin

Fanfwe

Member
Hello,
So, this is my first attempt at an Apple board repair.
I have a defective board taken from an A1502 2013 13' Retina MBP.

No sign of liquid damage, no obviously burnt component. Overall board visually looks in very good shape.

Board gives a green and then orange light on the charger, but no fan spin.

I have checked the power rails, and PPBUS_G3H is present at 12.58V
All S5 power rails are present and with good voltage
Nothing on S4 power rails.

Looking at the power switching circuits, the Enable signals for PP5V_S4 and PP3V3_S4 are low.
According to the schematic, they are driven by the PCH.

Not quite sure where to look at from that point. I've seen people suggesting to look at RTC and SPI flash.
I have a good 32Khz signal on PCH_CLK32K_RTCX1.

I also looked at the SPI_CLK signal, and I can see pulses there when I apply power to the board, then a steady 3.3V
One thing I don't quite understand is who is driving this clock. Because on the schematic, there's two SPI masters on the bus - SMC and PCH, which seems weird to me.

So, this is where I am at. Hopefully the PCH is not dead. Any idea where to look at next ? Is it worth it dumping and/or reflashing the ROM ?

Thanks in advance!
 

2informaticos

Administrator
Staff member
Try first to start in SMC bypass mode.
If nothing, post PM_BATLOW_L, PM_RSMRST_L, PM_PWRBTN_L and SMC_ONOFF_L levels.
 

Fanfwe

Member
Hi,

Board won't start in SMC bypass mode.

Levels are (with the board out of the machine, no battery plugged in):
PM_BATLOW_L 3.33V
PM_RSMRST_L 3.26V
PM_PWRBTN_L 3.41V
SMC_ONOFF_L 3.41V
 

2informaticos

Administrator
Staff member
OK then, all PM_SLP_Sx_L signals should pulse at same time, check that.
Also check for pulse at all big coils...
 

Fanfwe

Member
PM_SLP_S5_L, PM_SLP_S4_L and PM_SLP_S3_L all pulses from 0V to 3.3V when pulsing SMC_ONOFF_L
PM_SLP_S0_L however is a little weirder. After connecting charger, I get a pulse from 0V to 3.3V but then it goes down to about 2V (with a lot of ripple, too). Then each time I pulse SMC_ONOFF_L, I see a pulse from this 2V to 3.3V and then back to 2V.
I measured 120kOhms to ground on PM_SLP_S0_L, so the pull down resistor seems OK.

As for the coils, I can see permanent high frequency pulses on L7130, I can see pulses for a short time on L7520 when I pulse SMC_ON_OFF_L, nothing at all on L3905, continuous high frequency pulses on L7430, and nothing on L7310 and L7320. Hopefully I didn't miss any.
 

2informaticos

Administrator
Staff member
So no pulse at all at VCORE.
Inspect for corrosion around U1950 and check if ALL_SYS_PWRGD pulses at same time with all PM_SLP_Sx_L signals.
Ignore PM_SLP_S0_L, is not important now.
 

Fanfwe

Member
No signs of corrosion around U1950.
Nothing on ALL_SYS_PWRGD. Remains at 0V even when I pulse SMC_ONOFF_L

Looking at the schematic and ISL88042 datasheet, ALL_SYS_PWRGD will be pulled to ground until all 4 S0 rails are good. But my S0 rails (actually all rails from S4 and down) don't turn on, so I shouldn't be seeing any pulse on ALL_SYS_PWRGD, right ?
 
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2informaticos

Administrator
Staff member
If PM_SLP_S3_L pulses, some S0 voltages (controlled by it) should pulse too; check corresponding coils...
 
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Fanfwe

Member
So I checked PP1V05_S0, PP1V5_S0, PP3V3_S0 and PP5V_S0 and I get a pulse on all of them whenever I connect charger, or pulse SMC_ONOFF_L.
Special thing on PP3V3_S0 though, it actually never gives 0V. Averages at 1.94V and pulses to 3V3 when I pulse SMC_ONOFF_L
 

Fanfwe

Member
I get a pulse on pin 7, but not on pin 3.
So, I checked the other input of the AND gate on pin 6 (SMC_DELAYED_PWRGD) and no pulse there. SMC_DELAYED_PWRGD is not shorted to ground.
 

2informaticos

Administrator
Staff member
SMC_DELAYED_PWRGD appears after VCORE.

"Nothing on ALL_SYS_PWRGD. Remains at 0V even when I pulse SMC_ONOFF_L"
You cannot get pulse at pin 7 of U1950 if no pulse at ALL_SYS_PWRGD.
Please post correct information.

Check for pulse and short at all Power FETs from page 60.
Pay atention to C6412/22/32/42.
 

Fanfwe

Member
So U8050 doesn't give me a pulse on the output. But the enable signal from the SMC also doesn't pulse.

More interesting, I think, is on U8005. I do see a pulse out of it, but only about half a volt, instead of 1.05. I measure 175 Ohms to ground on PP1V05_S0SW_PCH_HSIO so it looks like this is where I have a short to ground, right ?

And yeah, I re-probed ALL_SYS_PWRGD for pulses and I get them. I must have probed wrong last time, sorry about that...
 
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2informaticos

Administrator
Staff member
"More interesting, I think, is on U8005. I do see a pulse out of it, but only about half a volt, instead of 1.05"
Is not easy to catch the peak pulse with multimeter.
An o-scope helps in such case.

"I measure 175 Ohms to ground on PP1V05_S0SW_PCH_HSIO so it looks like this is where I have a short to ground"
Doesn't look like short; compare with similar working board.

Did you check 4V5 and 5V power rails from audio area?
 

Fanfwe

Member
Yeah, I'm already doing those measurements with a scope, not a multimeter. So I'm 100% sure that the pulse out of U8005 is only 0.5V, not 1.05V.
Unfortunately I do not have another working board I can compare this to, but on all other power rails, I'm at least in the range of kilo-ohms, if not meg-ohms to ground, which is why I'm surprised by this 175 Ohms here.

I just checked PP4V5_AUDIO_ANALOG, PP5V_S0_AUDIO_AMP_R and PP5V_S0_AUDIO_AMP_L and all three are pulsing.
 

2informaticos

Administrator
Staff member
That is PCH power rail, so could have lower value than other rails.
What happens if you start without U8005?
 
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Fanfwe

Member
I desoldered U8005. Still no fan spin when connecting charger. Anything specific I should look at now that the chip is off the board ?
 
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