A1932 - Black screen, no startup sounds

[Strolch]

Apple MacBook Air 13" A1932 2018. It's on. Touchpad clicks and board gets warm. There is no start-up sound and the display stays black. The audio board was defective after liquid damage. Nothing is visible on the logic board. bild comes with another logic board. So display and cable are intact! I have both logic boards here and can also measure on both.

[Strolch]

Re: A1932 - Black screen, no startup sounds

From C8469-C8473 I have 43 volts on the board where the display works. On the board where the display remains black, I have 0.0200 volts from C8469-C8473!

[mon2]

Re: A1932 - Black screen, no startup sounds

Remove all power. Meter in resistance mode.

Check the resistance to ground on C8469-C8473 for the non-working board.

Compare the resistance to ground of the working board.

[Strolch]

Re: A1932 - Black screen, no startup sounds

All right around 168K ohms after a few seconds.

[Strolch]

Re: A1932 - Black screen, no startup sounds

possibly U8400

[mon2]

Re: A1932 - Black screen, no startup sounds

What is the 820-xxxx marking on your logic board ?

[Strolch]

Re: A1932 - Black screen, no startup sounds

820-1521-a

[mon2]

Re: A1932 - Black screen, no startup sounds

With the adapter & known good LCD connected, what are the voltage readings for:

1) F8400, pin # 1

2) F8400, pin # 2

3) R8442, pin # 1 (EDP_BKLT_EN)

4) R8442, pin # 2 (BKLT_EN_R)

5) I2C_BKLT_SCL

6) I2C_BKLT_SDA

7) I2C_BKLT_SCL_R

8) I2C_BKLT_SDA_R

[Strolch]

Re: A1932 - Black screen, no startup sounds

Then do I have to remove the display to measure? Or just remove the 6 screws from the display board and fold the display board over?

[mon2]

Re: A1932 - Black screen, no startup sounds

Compare notes with the working unit.

For the logic board with the working backlight, do you have the display connected ? Pretty sure that you will need to mate the display to allow for the logic board to turn on the backlight.

Respectively, need to check under the same conditions as the working board, if the backlight IC is being ENABLED on the non-working board ?

Is the DC input to the backlight fuse OK ?

The I2C pins are not stuck on the backlight IC ?

Proceed with patience and care to prevent damage.

[Strolch]

Re: A1932 - Black screen, no startup sounds

I had slipped while measuring near F8400 and wanted to test the board and installed it. Then there was some smoke and the U8400 burned out ;-( from the intact board!

[Strolch]

Re: A1932 - Black screen, no startup sounds

Then I'll probably swap the U8400 from the board first and see if it works again.

[mon2]

Re: A1932 - Black screen, no startup sounds

Ouch! They are commonly available on Aliexpress.

Being in this position, consider to flux and carefully remove the same IC off the non-working board and transplant onto this board and see if the backlight works.

Lots of flux & patience.

[Strolch]

Re: A1932 - Black screen, no startup sounds

I bought 10 pieces from Ali. I'm not sure if it fits this board. The the IC both the same? The numbers are not the same.

[mon2]

Re: A1932 - Black screen, no startup sounds

Perhaps a different housemark.

Did the vendor state the part to be the same as the original backlight IC ?

Worth testing with 1 device.

Post the bottom side pic of the new part. The defective one needs to be replaced of course but do make a note of the pin #1 orientation for this surgery.

[Strolch]

Re: A1932 - Black screen, no startup sounds

I also installed the IC in the A1707 15 inch MacBook Pro! On the schematics the IC on both boards Air and Pro are the same LP8548B1SQ_-04 and LP8548B1SQ_-03 and the same contacts

[mon2]

Re: A1932 - Black screen, no startup sounds

It should be fine to use.

[Strolch]

Re: A1932 - Black screen, no startup sounds

Das sind die IC die ich gekauft habe

[mon2]

Re: A1932 - Black screen, no startup sounds

That is a good store - have used them many times for parts. No issues.

[Strolch]

Re: A1932 - Black screen, no startup sounds

I unsoldered U8400. 3pins don't look good one pin is gone. Pin 8 is not connected. I will rebuild the 3 pins and solder in U8400. I hope the display will work again. Then I measure the other board.