MacBook Air A1466 820-00165-A 5V Rail Pulses (on & off)

[mferna14]

Hi all , I am working on a Apple MacBook Air A1466 820-00165-A logic board. The problem was no back light & all was working fine. I replaced the Backlight chip but still no display & now it does not even turn on. I replaced with a known good back light chip assuming the soldered chip was shorted. But still no luck. Now I measure voltage rails. 3.3V is perfect but 5V Rail Pulses (on & off). TPS51980A, 5V ENABLE pin 4 P5VS4RS3 EN R also fluctuates on & off. 5V comes & then shut off again. This happened continously. I checked for any short to ground, but none. When I check for where this signal is genrated, PM_SLP_S4_L also go on & off. Any help would be greatly appreciated. Thanks

[mon2]

Re: MacBook Air A1466 820-00165-A 5V Rail Pulses (on & off)

Hi.

Review this excellent website / webpage:

https://www.it-tech.com.au/mac-q-a/pm-slp-s4-l-timing/

[mon2]

Re: MacBook Air A1466 820-00165-A 5V Rail Pulses (on & off)

And...

https://logi.wiki/index.php/820-00165_Pulsing

[mferna14]

Re: MacBook Air A1466 820-00165-A 5V Rail Pulses (on & off)

Thanks you so much "mon2" for the knowledge above.. I will surely read tomorrow & let you know the out come.

[reformatt]

Re: MacBook Air A1466 820-00165-A 5V Rail Pulses (on & off)

If you are getting pulsing of rails up to CPU Vcore, then that is usually U6100 related. Make sure none of the termination resistors are knocked off or corroded.

If the display is detected, then you should see 8.6V on L7701 (means backlight enable is on and F7700 is ok), then troubleshoot U7701 from there (should have 25V on C7797/C7799). Don't forget to give J8300 a good clean too with IPA. I had one the other day that wouldn't detect the display until cleaning it, despite it looking perfect.

[mferna14]

Re: MacBook Air A1466 820-00165-A 5V Rail Pulses (on & off)

Thanks for the reply "reformatt"... Just for fun sake I re-programmed U6100, but still the same. As of now the Enable pin of 5V of U7501 is also pulsing. Yesterday I went through the power rails once again & observed that PP3V3 S5 is perfect but PP3V3 S4 is also pulsing. 3.3v comes & then off & on, though accordingly this rail should be AWON. I am still checking, it a challenge & have to repair it.

[reformatt]

Re: MacBook Air A1466 820-00165-A 5V Rail Pulses (on & off)

The only rails that are always on are PP3V42_G3H, PPBUS_G3H and the S5 rails. So your statement that a S4 rail is always on is incorrect. You need to check all rails up to CPU Vcore to see if they are pulsing. Also check if you have activity on pin 1 of C6100 with a scope.