A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-02016

[mon2]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Can you confirm that with a known good display, you indeed can see the screen graphics? Just the backlight is not working ? With a flashlight along the sides / front of the LCD, you can view the normal desktop graphics ?

Suspecting the meter may have issues.

[slimmy182]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

I confirm that with a known good display, I can see the screen graphics using iphone torch!

Using an other meter I confirm 'OL' reading for two RP842 pads. Anyway, pad 2 seems to reach 'OL' faster than pad 1 when number are raising.

[mon2]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Very good to know that your display is showing the graphics.

Post the voltage reading for IPD_LID_OPEN_1V8.

[slimmy182]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Very good to know that your display is showing the graphics.

Post the voltage reading for IPD_LID_OPEN_1V8.

I'm really sorry, but I can't find where is located

[mon2]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

See attached. This signal is used to enable / disable the backlight based on the position of the top lid.

[slimmy182]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Many thanks.

IPD_LID_OPEN_1V8 Measure 1.80V . That should be correct right?

[mon2]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Yes. This is a good reading. This means that the LID sensor is working and the logic believes the lid is in 'open' state. This signal enters U8100 IC which is the same chip that should enable the backlight.

The backlight may be enabled briefly if it believes the backlight circuit is drawing too much current. That is, perhaps the ENABLE is turned to HIGH but then a current sensor reports that too much current is being drawn for whatever reason and then quickly shuts it off so we are observing a logic LOW or OFF state with the meter.

Place your meter in resistance mode @ 2k scale. No power to the logic board.

Check and post the resistance for the following:

red meter probe on one side of RP853; black meter probe on the other side of the same resistor. You should have a reading close to 1k8 = 1,800 ohms.

If you do not see this value then switch to the next higher scale and test again.

This is only to confirm if the meter is properly reading the resistance.

After the above, place your meter in DC voltage mode (30V or higher).

Check and post the voltage readings for the RP801 & LCDBKLT_EN_L.

The LCDBKLT_EN_L signal has to be a lower voltage than what is being passed through from source & drain to ENABLE the mosfet @ QP800.

That is, the switching BOOST regulator @ UP800 pulls the line @ pin 11 (BKLT_SD) LOW to turn on the mosfet QP800 to pass through the voltage from PPBUS_AON.

[slimmy182]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

here it is:

Resistence to ground @RP853 = 1.780 ohms

@RP801 = 11.9V

LCDBKLT_EN_L = 11.2V (measured in RP802 and CP801) (CP801 is no stuff, right?)

Is that difference enought to enable backlight?

I also check @DP800 and is 0.3V in PAD A and 0V in pad Z

I noticed that RP845 show a little sign on it, see attached. Reading is 5.17V on both side

Inspecting display connector seems all right

[mon2]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

@RP853 = 1.780 ohms

Ok. Since you are in the 2k scale, this really means the resistance is 1k78 = 1,780 ohms. This is a good reading.

Can you review again the resistance to ground using the same 2k scale for:

RP842 - check each pad of this part.

Red meter probe on the pad; black meter probe to ground.

@RP801 = 11.9V

Good.

LCDBKLT_EN_L = 11.2V (measured in RP802 and CP801) (CP801 is no stuff, right?)

Is that difference enough to enable backlight?

No, afraid not. This is due to the switching regulator being disabled through pin # 17 which is with a low voltage. This low voltage passes through RP842.

At this stage, not sure why the enable pin is low. I think RP842 is off the logic board so the part is not mated with the driver chip U8100.

While we could force the mosfet to turn ON, this does not help till the IC @ UP800 is ENABLED via pin # 17 (UP800).

What is the voltage @ FP800? You have measured this one before but interested to know the exact voltage that ENTERS the current sense resistor @ RP800 and we know that 11.2 is on the exit. If the difference is too high, this could be causing the trigger of 'too much of a voltage drop = high load' so shut down the IC @ UP800.

With your meter in DC 20V scale, measure with great care as the parts are nested inside a dense area on the logic board:

the voltage on both sides of RD6C8.

PS: Have to do some drywall repairs but will be back later in the day.

[slimmy182]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

At this stage, not sure why the enable pin is low. I think RP842 is off the logic board so the part is not mated with the driver chip U8100.

Actually RP842 is on the board! I resoldered it back yesterday.

Repeating resistence to ground measurement for RP842 give me same results, 'OL' for both sides even if I use the max scale on multimeter.

measures for @ FP800 fuse is 12V both sides

@ RD6C8 = 0V , both sides

And again, thank you very much for your support. I hope to solve this problem and get back using computer as normal

[mon2]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Actually RP842 is on the board! I resoldered it back yesterday.

Repeating resistence to ground measurement for RP842 give me same results, 'OL' for both sides even if I use the max scale on multimeter.

This is a good reading which confirms there is no short circuit to ground on the ENABLE pin.

measures for @ FP800 fuse is 12V both sides

Can you confirm that the voltage is exactly 12V at the FP800 fuse ?

Downstream the voltage @ RP801 = 11.2 volts ?

[slimmy182]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Yes! I confirm 12V both sides of FP800 fuse, and 11.2V on @RP801

I just used two different multimeter to confirm it, same results. Variability is 0.01V

[mon2]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Remove all power. Meter in resistance mode.

Check & post the resistance to ground @ RP801 (same location as where you read 11v2).

[slimmy182]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Resistance to ground @ RP801 = 180.8 ohms (200k scale, if I use lower one 20k or 2k I get ‘OL’)

Sorry for being so late in reply to your message. Working in hospital leave me so little free time in that moment

[slimmy182]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

In the mean time I re-read measure, but this time whit the good LCD connected to the board, and I got:

RP842 = 1.8V pin 1 and 0V pin2 (It should be both pin 1.8V?)
CP842 = 1.8V pin 1 and 0V pin2

I2C_BKLT_SCL = 5.21V
I2C_BKLT_SDA = 5.21V

RP801 = 12V
LCDBKLT_EN_L = 11.3V (measured in RP802 and CP801)

FP800 fuse 12V both sides

RD6C8 = 0V


Only changes is that I see 1.8V on ENABLE pin now!



Anyway, have you guess why the mac is still "belive" it have LCD attached even if is really not?

[mon2]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Hi. RP842, pin # 1 @ 1v8 is a very good sign. Continue to use this LCD panel.

See attached.

Confirm the voltage on pad # 2 of RP842. It must also be 1v8 unless RP842 is not soldered properly or is damaged.

Consider to use the meter in resistance mode and remove all power -> check the resistance across RP842 component only (just tip to tip). This has to be close to 0 ohms.

What is the reading ?

Then move to measure from the pad of RP842 and then the pad where CP842 is located. Again, this should be close to 0 ohms unless RP842 is broken or not soldered properly.

Also recheck the voltage drop that is of concern. At the fuse is 12V but after the fuse is 11v2 ? See attached to confirm you are measuring at these sites.

[slimmy182]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

check the resistance across RP842 component only (just tip to tip) 0.00 ohms

RP842 pin 1 and CP842 pin 1 = 0.00 ohms

RP842 pin 1 and CP842 pin 1 = 480 ohms (2k scale)

No sorry for misunderstanding! In the two parts you indicated to me voltage is 12V! fuse is 12V and RP801 is 12V, my fault.

11.3V is for YELLOW PIN in attached schematics RP802 and CP801 (NOT RP801), in RED PIN RP802 = 10,60V

[mon2]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Ok. The voltage drop makes sense. These are good readings.

Confused about the following:

check the resistance across RP842 component only (just tip to tip) 0.00 ohms
* ok - good reading

RP842 pin 1 and CP842 pin 1 = 0.00 ohms
* ok - good reading

RP842 pin 1 and CP842 pin 1 = 480 ohms (2k scale)
* the reading changed to 480 ohms ?? Measured from where to where ?

If you short your meter probes together, the reading should be close to 0 ohms. This is what is expected between RP842, pin # 1 to CP842, pin # 1.

First confirm the resistance (no power to the logic board) is indeed about 0 ohms. Only then proceed to apply power to check that 3v3 is present on either side of RP842. Since RP842 mates with CP842 (pin # 1), you can measure @ CP842, pin #1. This voltage is important.

If the resistance is NOT 0 ohms then RP842 is not soldered properly or is defective.

Can you confirm again ? Respectively, when RP842 shows 3v3 on pin #1, this same voltage must carry through onto CP842 since it is a wire conductor between these 2 points. With the 3v3 voltage to the switching power supply, it will serve as the proper ENABLE signal.

[slimmy182]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

RP842 pin 1 and CP842 pin 1 = 480 ohms (2k scale)
[

Again sorry for confusing pin, I was doing faster.

This is right

RP842 pin 2 and CP842 pin 2= 480 ohms (2k scale)

the resistance across RP842 component only (just tip to tip) is 0.00 ohms

I re-soldered RP842, that mean is defective I guess. Can I put It upside down or is better to just put a jumper?

[mon2]

Re: A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-0201

Yes, RP842 is only a 0 ohm resistor. So you can remove it and apply a blob of solder to act like a short circuit.

The voltage on one side of RP842 must be the same as on the other side since this is just a short circut.

Once you are 100% sure of the soldering between these 2 pads only, apply power and the 3v3 voltage should reach the switching power IC (UP800) to ENABLE it.