820-2850 not turning on

ytesfay80

New member
I have an 820-2850 board. The customer told me there was a liquid spill a long time but they cleaned it up and it was working for a long time until it stopped turning on one day.
When I plug in the charger I get a green light but no fan spin or anything. I removed the board from the machine in order to test the power rails.

PPBUS_G3H - 12.59v
PP3v42_G3H - 3.4v
SMC_RESET_L - 3.4v
SMC_ONOFF_L - 3.4v
PM_PWRBTN_L - 3.4v

The current sensing pins on u7000 all measured properly.

PP5V_S5 and PP3v3_S5 are both present
PP5V_S3, PP3v3_S3 and the S0 rails are missing

I checked U7201 and these are some of the voltages I got.
Pin 1(ENTRIP1) - 0v
Pin 6(ENTRIP2) - 0v
Pin 4(TONSEL) - 4.96v

Is this an issue with the TPS51125?
 
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dukefawks

Administrator
First inspect board for corrosion closely. Check if 5V_S3 comes on for a fraction when plugging in the power.
 

ytesfay80

New member
I can't find any corrosion on the board since the customer said they cleaned the board after the liquid spill a while ago. I can see some probe points and pads on J2650 that look like they had liquid spilled on them.
I measured 5V_S3 and it is not coming on at all when the charger is plugged in.

I checked for PM_SLP_S4_L on R7912 and I got 0v.

Should I throw this is in the ultrasonic and see if that fixes it?
 

ytesfay80

New member
Okay I gave the board an ultrasonic cleaning and still no change.
With my multimeter PM_SLP_S4_L is not present at all even when the charger is initially plugged in.
 

ytesfay80

New member
Okay here are the measurements I took.
r1800 - Pin 1(3.41v) Pin 2(3.31v)
r1801 - Pin 1(3.41v) Pin 2(3.13v)
r1802 - Pin 1(3.41v) Pin 2 (3.40v)
r1803 - Pin 1(3.415v) Pin 2(3.409v)

I checked PM_PCH_PWRGD and PM_SYSRST_L and I got 0v. PM_PWRBTN_L and PM_SUS_PWR_ACK both show 3.4v
PLT_RST_L gives me around 0.25v as soon as I plug the charger in then it goes to and stays at 0v.

PM_BATLOW_L pulsed up to around 1.5v when the charger is first plugged in then it also goes down to 0v.

All of these measurements are done with only the board and no external components plugged in besides the dc-inboard and fans.
 
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ytesfay80

New member
Oh crap. I've been using a 60w charger this whole time. I will go to best buy and purchase an 85w charger.
 

ytesfay80

New member
Okay. I went and got a genuine 85w apple charger and it is still not turning on.
I re-took the measurements and they are the same except that PM_BATLOW_L is now pulsing almost every 5 seconds and goes up to around 3v then back to 0v and it repeats.
PM_PCH_PWRGD is also pulsing every 5 seconds and goes up to around 0.31v.

Update: Now when I check PM_BATLOW_L it pulses up to around 0.85v as soon as the charger is plugged in and doesn't come back high.
 
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ytesfay80

New member
I connected the battery then the charger but the charger light is staying green and not turning orange. Shouldn't it turn orange once the battery is detected and charging?

Anyways I left it on the charger with the battery connected so I will check on it in a bit. What should I do afterwards. Short the SMC_ONOFF_L to ground and see if it turns on?
 

dukefawks

Administrator
Well, that indicates a communication issue with the SMC. Check the data bus from SMC to battery on diode mode. But in your first measurements you say PPBUS @12.56V so SMC must be working. Disconnect battery indicator and try charging again.
 

ytesfay80

New member
I checked r5280 and r5281 in diode mode with no charger plugged in and this is what I got. The readings were the same for both resistors
Pin 1 - -OL
Pin 2 - -0.97v (Its showing what looks to be a negative number. Didnt know that was possible and the multimeter beeps the entire time I have the probe on pin 2)

In resistance mode both showed over 2kohms when the schematic says it should be 1kohms

The area around the ISL6259 looks clean with no liquid damage.
 

dukefawks

Administrator
Measurements do not make sense. No idea what you are doing here....Red probe to GND black to the data bus, multimeter on diode mode. No power and battery of course!
 

ytesfay80

New member
When you say the data bus are you referring to the 2 resistors R5280 and R5281 correct?

I had the battery plugged in which was probably causing those bad readings. I removed the battery and measured in diode mode with red probe on ground.
Pin 1 - 0.38v
Pin 2 - 0.503v
The measurements were the same for both resistors.

Also, In resistance mode they are both measuring 2kohms.
 
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