820-3476-A No Power Issue

[ddahlstrom]

I have a macbook pro A1502 (13" Mid-2014) with board number 820-3476-A that no longer powers on. When only fan and DC-in board/power cable is plugged into motherboard, I get fan spin that gradually accelerates as well as a green-then-orange light on charging cable. When the macbook is fully assembled, I do not get any lights on the charging cable or signs of life from computer. The main power rail is present, any ideas on where to look? Thank you.

 

[dukefawks]

History? Liquid? Is CPU Vcore present on L7310?

 

[ddahlstrom]

Does not appear to be any liquid damage (although plenty of dust/hairs everywhere). Laptop has supposedly been through regular wear for a couple years. It died and no longer powers on or does anything except when I have motherboard out of computer. Will check for Vcore on L7310 and let you know what I find

 

[ddahlstrom]

CPU VCore was present at L7310 at (1.7V). On the schematic it is listed as PPVCC_S0_CPU_PH1 which blends with PH2 to make PPVCC_S0_CPU. Both phases are present and at proper voltages. CPU is getting warm when board is out and adapter is plugged in. Also, after further testing, I have realized that P3v3S0 is missing from all points I tested on the board. Found the 3v3_S0 switch (U8030) and found that the P3v3s0_en signal is missing. It is my understanding that this switch is what sends the signal to CPU to activate S0 (on) state. Since the enable signal for this switch is missing, then the chip would never tell computer to actually switch to on state. Am I understanding this correctly?

 

[dukefawks]

PP3V3_S0 must be present for CPU Vcore to be there. Double check that Vcore is present and 3V3_S0 is really missing, it should not be happening.
Also the enable for U8030 comes straight from all the other S0 enables, so check voltage on both sides of R8186.

Don't use comments, use reply.

 

[ddahlstrom]

You were right dukefawks. I rechecked my measurements and found that CPUVcore is present as well as the 3.3v enable signal for U8030. I took a bunch of measurements and observed operation. With board installed into computer, I get a green/orange light, but no fan spin and no other signs of life. When the board is external with only fan and DV cord plugged in, I get green/orange light as well as fan spin and a warm CPU. Main power rails are active and I took some measurements and thought I would record some of the more important ones here to help with troubleshooting:

Vcore present:
3v3 enable at U8030 present
All 5V rails present for S5-S0 states
5VS5 present at C7505
PM_SLP_S0_L present at pin 1 of U1420
3V present at pin 2 of R8162
Also verified that all S3 rails for each state are present as well

For the most part it seems as if the power rails are active and present. Any more ideas on where I should check? Heck it could even be hardware at this point but I am pretty sure I ruled that out already.

 

[ddahlstrom]

Was able to determine that it was the I/O board attached that was shorting out the computer. As soon as the connector is plugged into J9500, I only get orange light and no fan spin. With everything plugged in besides J9500, the entire computer powers on and works fine. Why do you think this is happening? The board number for the I/O board is 820-3539-A. The daughter board looks very healthy and devoid of corrosion/burnt areas.

 

[dukefawks]

No use in diagnosing an IO board, first try a known good one including cable. The board should work fine without it connected, so test that too.

 

[ddahlstrom]

The computer works great without the cable plugged in, although the trackapad is incredibly laggy at the Admin sign-in screen but works fine once signed in.

 

[dukefawks]

That is normal because it is missing a few thermal sensors. Get another IO board and cable and see if that fixes it.