820-00281 No Power

CRC2018

Member
So my second 820-00281 in as many weeks. Customer advises they were watching youtube when it just shut down no power. Have taken it in and board looks very clean but is exhibiting the following behaviour:

With battery plugged in i'm not getting PPBUS generated and my charger isn't able to power the machine - my usb c ammeter just keeps cycling on and off. With the battery unplugged I am getting PPBUS voltage at 12.6V and correct negotiation of the charging voltage from the charger. The board however still won't power up i've checked some common voltages:
PP3V3_SUS - present
PPBUS - present 12.6v
SMC_ON_OFF_L sits at 3.3v but does drop to 0v when power button pressed.
SMC_LID sits at 3.3v when lid open and drops to 0v when lid closed

When I initally connect my charger / usb c ammeter to the board when it's bare after negotiating the correct charger voltage I get a brief current surge to 1.5a then it drops down to 0.0a and stays there.

I haven't delved to much further into this one yet however would appreciate any advice in where to look first or if there is any common issue with the behavior I have described!
 

2informaticos

Administrator
Staff member
If you get that high current pulse, means the board tries to start and many secondary voltages should appear in that moment.
So check for pulse at all big coils.
If no pulse, check for short then.
Also check ALL_SYS_PWRGD.
 

CRC2018

Member
Seeing a quick pulse on the PP5V5_S4 and PP3V3_S4 power rails to 5v and 3.3v. ALL_SYS_PWRGD - missing, the S0 rails don't pulse - only seem to have S5 rails after the pulse. Should also add I checked PM_SLP_S4_L which is low 0v.
 
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2informaticos

Administrator
Staff member
So you get a pulse at PM_SLP_S5_L, but no reaction at all at PM_SLP_S4_L?
Trigger SMC_ONOFF_L and check again.
Also check P5VS4_PGOOD.
 

CRC2018

Member
Yes pulsing PM_SLP_S5_L - cannot seem to see any pulsing of PM_SLP_S4_L
P5VS4_PGOOD is not present although R7801 seems good.
Should add - no pulsing at all with SMC_ON_OFF_L only when i replug charger then i get the quick pulse then off to S5 state again.

Should add as well that after more testing I am seeing a pulse on the S0 Rails for less than a second.
 
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2informaticos

Administrator
Staff member
"Seeing a quick pulse on the PP5V5_S4 and PP3V3_S4 power rails to 5v and 3.3v."
In this case, P5VS4_PGOOD should pulse too.

Post diode mode to ground at L7600.
You may need to change U7650.
 

2informaticos

Administrator
Staff member
Is better to use an o-scope to catch fast pulse on the coils.
It will also show if the pulse reach the nominal value expected.
ALWAYS check on coil output pin connected to filter capacitor.
 

CRC2018

Member
Diode reading at L7600:
Pin 1 - 0.418
Pin 2 - 0.417

A scope is something I am thinking of investing in but currently do not own!
 

2informaticos

Administrator
Staff member
So PM_SLP_S4_L pulses.
In the same way, check PM_SLP_S3_L and all big coils.
Also check all power rails from page 74, Power FETs.
 

CRC2018

Member
PM_SLP_S3_L is also pulsing - all other rails (at big coils) appear to be pulsing.
One strange behaviour appears that PM_SLP_S0_L pulses to 3.3v then drops down to 2.75v and stays there after everything else has pulsed
 
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CRC2018

Member
Update - in SMC bypass mode it starts and runs. So we looking at bad SMC? Presume i'll need to get a donor SMC off another 820-00281 or are the ones from the 12" Macbook compatible?
 

2informaticos

Administrator
Staff member
I don't think to be SMC.
In fact it detects a problem and stops the board; some sensor triggers it.
Instal HWMonitor and look for strange I/V, or temp values.
 
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CRC2018

Member
Well I thought i'd have a go and reflow SMC anyhow - board now powers up in normal mode but not with battery connected. Looks like i've got a dead battery as well.
 

2informaticos

Administrator
Staff member
Is the battery recognized at least?
Which is exact PPBUS_G3H voltage?
Post diode mode and voltage at SCL/SDA lines of battery bus.

I also recommend to reball SMC, if reacted to reflow.
You had a bad contact for some SMC sensor line...
 

CRC2018

Member
PPBUS_G3H Without Battery - 12.61V

System will not start with battery connected but if I connect it after turning system on it recognizes it and says 2% not charging. Also PPBUS_G3H Voltage slowly raises from 12.61v up to 13.02V with the battery attached.
 
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