820-2838 No PP3V3_S3

[Japtastic]

Hi, I'm fairly new to logic board repair and schematic reading / electronics although I have been in the IT repair business for the last 20 years.

I'm trying to work out my first logic board repair and may well have got confused along the troubleshooting route. Could do with a helping hand!

These are my test results / notes:

PPDCIN_G3H = 14.8v SCHEMATIC SAYS 18.5v ??

PPBUS_G3H = 8.35v SCHEMATIC SAYS 8.4V

PP3V42_G3H = 3.29v SCHEMATIC SAYS 3.42v

PP3V3_S5 = 3.2v SCHEMATIC SAYS 3.3v

PP3V3_S3 = -- SCHEMATIC SAYS 3.3v

PP5V_S3 = -- SCHEMATIC SAYS 5v

R7910 Pin1 = 3.26v Pin2 = 3.11v 47k ohm tested ok
C7911 Pin1 = 3.29v Pin2 = 3.17v
C7910 Pin1 = 3.1v Pin2 = 0v
Q7903 Pin1 = 0v Pin2=G Pin3 = 3.25v
Q7910 Pin 4 = 3.29v Pin 3 = 3.11v Pin1,2,5,6 = 0v

There is no obvious water damage to the board and everything looks great and very clean.

Am I right in thinking the next step is to replace Q7910?

Of course, I could be mis-reading the schematic entirely and have the completely wrong end of the stick...

Cheers

Stewart

 

[aprendiz]

Press power button or use power pads on the logic board.... This board does not power on by itself....

 

[Japtastic]

Thank you, I thought they all turned on when power was given! Lesson learned. I do now get very fast fan spin and hot CPU. This leads me on to another problem but I will troubleshoot first before posting again.

I'm still not completely clear on where my logic failed. Everything looked like PP3V3_S3 should have turned on with the values I was testing? An explanation on where I went wrong on this would help me greatly.

 

[aprendiz]

In order to have PP3V3_S3 you need P3V3S3_EN, this signal came from MCP and is sent only after press power button...

 

[dukefawks]

Fan spins fast because trackpad is not connected. Put it back together including battery and test again.

 

[Japtastic]

Thanks chaps. I will have to wait to test it once I get the rest of the machine sorted, also waiting for some donor boards to replace a couple of caps.

Am I right in thinking that my logic was nearly correct? The voltage at the gate was only slightly lower than the source but it was looking for 0v aka P3V3S3_EN_L so it could open? From my tests this seems the case.

Also is this expected / normal? PPDCIN_G3H = 14.8v SCHEMATIC SAYS 18.5v

 

[dukefawks]

You are looking for problems that are not there. Put this thing together and it will most likely be working.

PPDCIN will depend on what voltage your charger puts out. Apple is lazy and copy paste this stuff from other diagrams. Output voltage between 45/60/85W chargers are all different.

 

[Japtastic]

Thanks for the info. I'm no't looking for problems just trying to learn the way these components work together. First time reading a schematic so it was a general question on P3V3S3_EN_L and the MOSFET.