Only 1 second of backlight
I've been trying to diagnose a problem with mid 2017 A1534, board 820-00687.
Doesn't turn on.
When trying to turn on, LCD backlight comes on for about one second, and nothing happens after that, also there is no image while that happens or after (when shining a light on LCD).
Negotiates and takes 20v properly from charger.
Gives a chime when connecting the charger.
I'm a complete novice in board level troubleshooting, so don't be surprised if I don't know something obvious. I did read up everything I could find.
So far I think I've narrowed it down to something around the L8410 inductor.
Schematic says that after the inductor voltage should be around 45v, while instead it's 8.6 exactly like before it.
I assume something should pulse the input into it to boost the voltage for the backlight, but there is no pulsing. Just stable DC.
Probably that "something" is U8401 which controls the Q8406 MOSFET which should be doing the pulsing.
Are there any preconditions to U8401 initiating the pulsing? Or should I assume that it's dead?
Edit: BKLT_EN_R coming from CPU to U8401 does go to 3.3v and stay there.
Update (02/15/2023)
As for the differences, I'm using a brd file for 820-00244, so far the only difference I found was at the XW8401 slot, which shows a component in the file but not present on the board.
Is dit een goede vraag?
7 opmerkingen
@hellomacos - You know?
door Ben Capehart
@beanman56
Thanks for tagging me in:-)
door HelloMacOS
@con_el_queso
Have you tried a different display?
The fact you get 20v(20v is booting) looks promising but the 1 second if backlight concerns me,these models suffers from a issue called flexgate which can cause these sorts of issues
I would try with no display attached(not for long though)just to see what results you get
Also have you tried it in a external display?
Thanks:-)
door HelloMacOS
@hellomacos Hi there, thanks for the reply.
Nope, I have no access to a different display because I don't do any of this professionally. Had a dead laptop laying around and decided it couldn't get any dead-er, so might throw my all at it.
Your mention about flexgate got me researching and I couldn't verify that A1534s were in fact affected. Could you point me to resources about that?
I have tried external display just an hour ago and no luck. But I don't know whether I did everything right while attempting.
door The Man Himself
@con_el_queso - This MacBook series didn’t encounter the MacBook Pro 2016/17 systems did with a short cable on the backlight cable.
door Dan
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