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820-00165 A1466 - backlight/image/randomness...

J

jpadie

New member
i have just started looking at this board. lots of rubbish all over it but no real corrosion to see under a scope.
plugged it in and the board started up with no orange light. green light, chime, fan spin and image but no backlight.
I replaced the backlight driver and backlight was back.

replaced the flex cable to DC-In board and I got the orange light.

then the backlight became intermittent (turning on/off irregularly). then the image sometimes did/sometimes didn't appear at all. then sometimes the machine stays on continuously drawing 720mA and sometimes it drops down to 20mA (no s5 rails, measurable g3H rails present, but can't check the clock as it's under the board and this symptom has not appeared with the board out of the chassis).

measuring backlight voltage with the screen unplugged shows a descent from 30v all the way down to 8.56v.

CPU getting too hot to touch, FYI (with heat sink, new paste and fan on).

any clues?

Edit
Unexpected shutdown now occurring when board is out of chassis . All g3h rails confirmed present

Shutdown doesn't occur when flex cable (brand new) is unplugged. CPU powers and heats up in this state.
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
Does the MLB stay on if LIO flex is disconnected?
If yes, then try other LIO board/flex.
Also check LIO connector for corrosion, on MLB.
 
J

jpadie

New member
Does the MLB stay on if LIO flex is disconnected?
Click to expand...
Yes

If yes, then try other LIO board/flex.
Click to expand...
Done. Same behaviour.

Also check LIO connector for corrosion, on MLB.
Click to expand...
No corrosion. But pins 19 (SYS_ONEWIRE) and 27 (SMC_LID) are blackened.
continuity between the pad and the connector is fine on both those pins. and of course the keyboard is not plugged in.
 
J

jpadie

New member
I have used an original magsafe and a version wired up to my bench power supply.

I'm now not getting any spin up with the flex cable installed, and without the flex cable I get vCore.

tried three different IO boards and three different cables. All rather odd!
 
J

jpadie

New member
fan spins with no flex cable. vcore comes up.
didn't check for USB activity.
But as you recommended I tried an original mac charger instead of a bench supply and it the board spins up just fine with the LIO connector in situ. I don't understand why though! in the magsafe2 cables there are only two wires so the charger can't be adding any intelligence over what is inside the magsafe port. And my cables were original apple ones! Any thoughts? The board is drawing about 10W with the battery plugged in
I will plug in a screen over lunch and see whether the back light issue persists.
thanks.
 
J

jpadie

New member
Screen backlight is good and stays on now.

But the display has now developed the "footlights" issue. Perhaps a badly seated cable.
 
2informaticos

2informaticos

Administrator
Staff member
Magsafe 2 handshake protocol is different than first model.
Since 2015, 1-->2 adapter can generate weird issues, like backlight one.
 
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