820-3476 Retina liquid damage

[arnonabuurs]

Hi guys I have a Retina 3476 that had a tiny liquid spil on U7501, see attached images. Rest of board looks good.

- 12.65v coming in at pin 23 VIN
- 3.43v at pin 21 S5_PWR_EN
- 3.43 at pin 12 SMC_PM_G2_EN
- 0v at P5VS4RS3_EN Pin 4

Seems I need to troubleshoot the P5VS4RS3_EN signal which I did:

- R8179 = 0 ohm and 0v
- R8175 = 0 ohm

- R8178 = 100ohm
- U8180 = 3.34v on pin 5 ov on Pin 1
- R8185 = 0 ohm
- R8184 = 330ohm
- R8186 = 36.6k (schematics says 39K, checked another board its 37K should be OK?)
- R8187 = 0 ohm
- R8183 = 325 ohm
- R8188 = 58k ohm (schematics says 68k, another board I have is also 58 so seems OK)

Any suggestions what to look for? Whats should PM_SLP_S3_L show for voltage? Any suggestions welcome.

 

[arnonabuurs]

UPDATE: got a spinning fan but not starting up, no chime. Tried PRAM to no avail.

 

[dukefawks]

CPU Vcore present? USB mouse lighting up?

 

[arnonabuurs]

CPU Vcore present? USB mouse lighting up?

OK will check tomorrow. I have an idea the CPU is the issue as soon as I turn the Mac on, the fan spins and cpu gets very hot. The fan will turn off and then on again etc.

 

[dukefawks]

If the fan is on/off it is power cycling. Also check for corrosion around BIOS chip/clock chip and diagnostic connector.

 

[arnonabuurs]

There is as good as no corrosion it was just a tiny spot in one place, checked all board with microscope. Tomorrow I will check again.

 

[arnonabuurs]

No light on Mouse and no vcore present

 

[arnonabuurs]

OK so now the fan stopped spining and im back to no PP5V_S4 ^^ ...great

 

[dukefawks]

Did you clean around the TPS51980? Just ultrasonic the whole board and inspect those traces at the TPS51980.

 

[arnonabuurs]

Yes the board was already very clean it was just one drop in some leg of TPS51980, we replaced it. 3.3v coming out just no PP5V_S4. Well, I did get a spinning fan before. I try clean again. Do these boards power on automatically when charger is plugged in?

 

[arnonabuurs]

Update: cleaned it all again, assembled together now it again starts spinning, 2-3 times then it stops. I measured CPU Vcore it was 1.74v at R7310 oin 1 and then drops to 0 and fan stops spinning.

Another update, now i kept it on the charger for a longer time with battery connected. The fan starts spinning max and does not switch of anymore. CPU VCore is at 1.739v. The USB can power an external drive, but mouse doesnt light up.

Edit: could it be current sensing issue?

 

[dukefawks]

Check the resistors in the SPI ROM data lines and check around clock chip

 

[arnonabuurs]

R6103 = 81k and on another board I have 99K according to schematics, to much difference so replace?

 

[dukefawks]

No, you are measuring in circuit so 81K is fine. It is the low value ones 15 and 45 ohm I think that always corrode.

 

[arnonabuurs]

the board has 0 sigh of corrosion though. I checked them all the rest is OK, on to the clock chip now