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

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pblegault

New member
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?
 
larossmann

larossmann

Administrator
Staff member
have you checked resistance between pins 17/18 and pins 27/28 of U7000?

If you put 18.5v from a bench PSU on the main DC in rail, disconnect the main fuse, and plug in the charger, can you turn it in? the idea here is that the laptop can talk to the charger and acknowledge that it is plugged in via onewire circuit but get its power from the bench PSU rather than the magsafe. remove F6905 and put the 18.5v from the bench psu on pin 2.
 
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pblegault

New member
Hi Louis,

We tried with the bench power supply and we have the same exact problem. The resistance between 27/28 is 21ohm and resistance between 17/18 is 3.2ohm. Any other idea?
 
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pblegault

New member
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.
 
larossmann

larossmann

Administrator
Staff member
pblegault said:
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.
Click to expand...
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.
 
larossmann

larossmann

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

larossmann

Administrator
Staff member
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

Crizz

Member
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?
 
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