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Finally got around to continuing work on this machine. U9701 was replaced and now I get no power, no chime, just a quarter fan spin. When I listen close there is a buzzing sound coming from the fan when I press the power button. Magsafe light is ok, green at first then red because battery is...

Removed U9701 and checked all traces, everything OK there. Ordered replacement U9701 and will see where that takes me.

PRAM Reset was done, issue persists. BKL_PWM (measured on C9704 and R9704) = 3.3V

Tested with good display, also no backlight. Unit chimes and Image is visible with flashlight. No liquid damage that I can tell. Having difficulty narrowing down the problem. Here's what I got so far: C9799 - 12.52V C9797 - 12.52V C9796 - 12.52V L9701 - 12.55V R0910 - 12.5V U9701 - 3.1V pin 3...

Ah, figured it out :) Will make the measurements tomorrow.

Ah yes... Diode mode. The one thing I've never used and am unable to figure out how to use. Maybe my meter doesn't do/support it? Been meaning to ask how to do that. Only diode symbol I see is the setting I put it on to check continuity so all I get is beeping, no readout.

Continuity is ok from pins 3 and 4 to R7750-R7753 and probe points to U7700 (I see no means of measuring actual U7700 pins without removing chip).

Where would I find lp8550? Doesn't show on schematic or bv. I went over the entire board several times, it's pretty much like new.

By following the schematic best I could and with the help of two other posts on this forum: - https://www.rossmanngroup.com/boards/forum/board-repair-troubleshooting/19199-solved-820-4924-no-backlight -...

Thanks for sharing Louis!

KG display arrived, Mac is in perfect health. Lesson learned; test everything myself even if others have tested it already. Thanks for the help along the way guys :) (I don't know how to mark posts as solved, can an admin do so pls?)

Removed both, issue resolved. Thanks dukefawks

No cracks in either, they actually look perfect (though that may have been the alcohol on it that cleaned them), still remove 'em?

Hah you may have just jinxed me ;) Easy fixes are nice but they don’t make for a great learning experience. Will inspect closer and remove the culprit shortly.

No liquid damage or drop damage, no previous work done on this Mac. I get the appropriate light on the magsafe and it responds to SMC reset. No power to the machine though. I checked PPBUS_G3H and get 0.686V at F7140 Also get: PP3V42_G3H at C4850: 3.43v PPVRTC_G3H at C1910: 3.43v PP5V_S5 at...

That did the trick. Mac powers on and is running ASD now. I don’t understand it but I won’t question it :) Thanks dukefawks

Heh as long as I can make it "not coming back for a power issue" ;)

Thanks dukefawks, Not doubting your experience but curious as to why I shouldn't bother putting a new one back? Schematic mentions "critical" and judging from the intense heat there's a lot of power flowing there. Also, would tinfoil deflect enough heat away from the plastic connectors next to...

G'day, Got an 820-3662 that just stopped working one day, no liquid damage or drop damage. Right now the magsafe responds to an SMC reset but otherwise it's a brick. Found (the hard and painful way) C7620 becomes incredibly hot within seconds after connecting power. I can say I've never felt...

KG display en route. Should get here same time as fine meter probes. To be continued.