820-2879 magsafe light no power ( q7085 voltage fluctuate )

[pblegault]

The voltage from the Q7085 ( PPDCIN_G3H-INRUSH ) is fluctuating from 0 to 18.5V. The 12.6V RAIL also go to 0V to 12.6V every second. I replaced the U7000, SMC, Q7080, Q7085. I also check all resistances near of U7000 and everything is good. The magsafe light is green but no power.

There is no short to ground on all coils.

Does anyone recognizes this problem or has any idea what could cause this?

 

[pblegault]

With a battery I am getting orange light. Battery is charging and the computer will try to start but after 3 try the fan will spin to maximum and there is no video.

 

[pblegault]

When I mesure on the 12V rail i get 3.4V then 12V then 3.4v ....

 

[larossmann]

With a battery I am getting orange light. Battery is charging and the computer will try to start but after 3 try the fan will spin to maximum and there is no video.

Is CPU vcore and MCP vcore present? Does it chime?

If CPU and MCP vcore are present and there is no chime, my guess here would be dead MCP or corrosion under the MCP.

This is a really shit machine to be doing anything to. core 2 duos always are.

 

[pblegault]

Hi Louis,

MCP Core and CPU core = 1V

 

[larossmann]

you answered only part of the question

 

[pblegault]

Hi,

Sorry Louis. Thank you for answer.

There is NO CHIME. Only fan spinning.

MCP CORE: 1V
CPU CORE: 1V

 

[dukefawks]

Resistance to GND on 3V42 bus?

 

[pblegault]

96 kilo ohm

 

[pblegault]

This is from L6995 to ground.

 

[larossmann]

My best guess is that something got under MCP89. I would do a light reflow and see what happens.

 

[pblegault]

Hi, I did a reflow and I get the same problem

Don't know what to do.

 

[pblegault]

Anybody have the same issue? I have 3 boards with the same issue.

 

[larossmann]

At this point I'd trash it. It's old. All the BGA chipsets available to fix this machine will be pulled from other boards, that were thrown away, because they too had a dead MCP89.

 

[Crizz]

Louis is right use it as donor board. But if you want to fix it, put it away, get yourselves a day off, forget about it, enjoy the sunny day, go to the beach, relax and then come back with new motivation and treat the machine as never touched it before! Measure all the rails from the beginning and make sure you miss nothing!
That's how I fix my nightmare boards.

Did you inject 18.5v on DCIN or 12.6v on PPBUS?
Did you removed the fuse from PPBUS while injecting?