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**EdwardGeo** · 10-01-2021, 12:45 PM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

PP3V3_LCDVDD_SW_F = 0v
PP3V3_S0_LCD_F = 3.3V
PPVOUT_SW_LCDBKLT = 0v

**mon2** · 10-01-2021, 01:39 PM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Which logic board # ?

Should be

820-2530
820-2879
820-2936
820-3115 (perhaps this one for mid-2012?)

See attached.

1) Post the voltages @ 1 and @ 2 for the series ferrite bead (L9004) on the LVDS power rail. If the voltages are 0 volts -> power down and remove all power.

Meter in resistance mode. Check and post the resistance to ground for the same @ 1 and @ 2 locations.

2) Then repeat and post the voltages and resistance readings for @ 3 & @ 4 locations on the logic board.

Attached Files

**EdwardGeo** · 10-01-2021, 02:47 PM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Originally posted by mon2 View Post

Which logic board # ?

Should be

820-2530
820-2879
820-2936
820-3115 (perhaps this one for mid-2012?)

See attached.

1) Post the voltages @ 1 and @ 2 for the series ferrite bead (L9004) on the LVDS power rail. If the voltages are 0 volts -> power down and remove all power.

Meter in resistance mode. Check and post the resistance to ground for the same @ 1 and @ 2 locations.

2) Then repeat and post the voltages and resistance readings for @ 3 & @ 4 locations on the logic board.

Thanks for quick reply. I did stress test on replaced cable and found short on led reverse or led backlight one of wires. If press on bottom of laptop, the cable touches the bottom case. So I do think that this is engendering issue or material which are made to be easy recycled.

Anyway if add little pressure on original cable, the 4th led return or reverse will get a short. Actually all wires isolation looks very bad. After cable disassembly I found signs of small burn.

So I think that the dead ic that controlling backlight is controll vdd. As short already have gone, possibly replacement of the ic will solve this problem.

Thank you, will measure voltages as you recommend

**mon2** · 10-01-2021, 04:00 PM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Confirm the logic board # when convenient but believe the backlight for the LCD will be TI # LP8550

Arrow currently has stock of these:

https://www.arrow.com/en/products/lp...as-instruments

We have free international shipping. It helps, can try to drop ship it to you - to date, any address we select appears to be with free shipping - including to our suppliers in Asia. We have replaced these in the past with success on backlight cases but of course you will need to review the other raised concerns.

If you have not done so already, from personal experience - good flux (Amtech or a good clone of it) + hot air tool at low pressure (30-35%) but high heat (500C is what we found works on our tool). Then gently nudge the IC with tweezers till it starts to dance. Finally lift the guy off the logic board.

Coat the WLCSP backlight pads with leaded solder (low temp solder) by skimming across the pads with a blob of solder on your soldering iron tip.

Flux again and remove the excess solder with good desoldering braid. If the braid gets stuck - DO NOT force it off else you may rip off a PCB pad = game over on the repair. Just use higher heat to melt the junction and remove the desoldering braid. Then use IPA (alcohol) to clean the pads.

Flux again and apply the new IC. The IC is small - at least to my naked eyes (we have not purchased a soldering microscope yet) - go slow till the solder balls melt and sink into place.

Suggest for you to source a few of these backlight ICs for service / practice.

**piernov** · 10-02-2021, 12:52 PM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

As always no point in troubleshooting backlight if there is no image...

**EdwardGeo** · 10-03-2021, 02:05 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Originally posted by piernov View Post

As always no point in troubleshooting backlight if there is no image...

there is no image, because there is no voltage on LVDS panel, so it cant operate.

The short was on old cable, which crumbled under the influence of time, the voltage Vdd 3.3v which goes to panel is made by same IC as backlight.

Waiting for replacement IC, hope that there is no other problems

**EdwardGeo** · 10-03-2021, 02:36 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Where can i find operation sequence of lvds?
How system making lvds working?

**EdwardGeo** · 10-03-2021, 03:13 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

What if chipset is not enable vdd for lvds?
That happens if S0 not talk back to chipset via I2C?

**piernov** · 10-03-2021, 07:10 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Yes LCD must be recognized properly by the chipset by reading EDID through DDC I2C bus before LCD power rail is enabled.
Also LCD power rails will be disabled anyway if lid is closed. (SMC_LID low)

**EdwardGeo** · 10-04-2021, 06:46 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

SMC_LID = 3.3V
LCD_IG_PWR_EN = 0v
LVDS_DDC_CLK and LVDS_DDC_DAT = 3.3v
PP3V3_S0_LCD_F = 3.3V

So possibly display died or chipset?

**EdwardGeo** · 10-04-2021, 06:56 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Originally posted by mon2 View Post

Which logic board # ?

Should be

820-2530
820-2879
820-2936
820-3115 (perhaps this one for mid-2012?)

See attached.

1) Post the voltages @ 1 and @ 2 for the series ferrite bead (L9004) on the LVDS power rail. If the voltages are 0 volts -> power down and remove all power.

Meter in resistance mode. Check and post the resistance to ground for the same @ 1 and @ 2 locations.

2) Then repeat and post the voltages and resistance readings for @ 3 & @ 4 locations on the logic board.

the board is 820-3115-B

PP3V3_S5_LCD = 3.3V
L9004 = 0 Ohm \ 0V
L9008 = 55 KOhm \ 0V
LCD_IG_PWR_EN = 0v

Attached Files

820-3115-B.zip (1.61 MB, 33 views)

**EdwardGeo** · 10-04-2021, 07:03 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

deleted

**mon2** · 10-04-2021, 10:06 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

L9004 = 0 Ohm \ 0V

Ouch!!

Remove the LVDS screen and all power. Measure and post again the resistance to ground on L9004.

**EdwardGeo** · 10-04-2021, 10:40 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Originally posted by mon2 View Post

Ouch!!

Remove the LVDS screen and all power. Measure and post again the resistance to ground on L9004.

Thanks for quick response.

I disassemble lcd and trace the ddc I2C signal, this goes to rom ic, I think that this contain edid image. I think that need to measure the clock with frequency meter. If there is no data talking then possibly the chipset dead?

**mon2** · 10-04-2021, 11:07 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Hi. See attached. L9004 is the power to the LCD display via pins 2 & 3 on the LCD connector.

Is it this ferrite bead where the resistance to ground is 0 ohms & 0 volts (when powered) ?

If yes, remove the LCD and check the resistance again.

Do you see the same resistance @ C9011? C9012 ? If yes, remove each carefully and then measure the resistance again to ground.

Review the trace from U9000 to this FB for the resistance. There is a short somewhere on this line.

Attached Files

**EdwardGeo** · 10-05-2021, 12:12 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Display datasheet:

https://cdn.badcaps-static.com/pdfs/...9d48ed29e7.pdf

Not sure, but seems the one I have

**mon2** · 10-05-2021, 04:56 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Ok. What is the status of the short on L9004 rail ?

Remove the display and confirm the resistance to ground on L9004.

**EdwardGeo** · 10-05-2021, 09:28 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Originally posted by mon2 View Post

Ok. What is the status of the short on L9004 rail ?

Remove the display and confirm the resistance to ground on L9004.

L9004 to GND = 20 kOhm and goes to infinity

I done I2C capture and seems the display is not sending data. But chipset is doing his job, not sure if that is correct (i do have only i2c sensors debugging experience) but add Sealogic projects. So DDC talk to lcd is present, but no answer. Tested all pin connections from Main board to LCD board, resistance are okay. Tested LCD board on short, heat - nothing...

Attached Files

**EdwardGeo** · 10-05-2021, 10:16 AM

Re: MacBook Pro 13.3 mid 2012 - a1278 - no internal display

Can I force bypass edid read and power on 3.3 v to lcd vdd to check if lcd will power on?

Or read eeprom with programmer to be sure that this one is working?

Actually if any lvds display have same power on sequence, I can use any display to capture it and understand how that works. And replace display or if data exchange is incorrect, replace chipset

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MacBook Pro 13.3 mid 2012 - a1278 - no internal display

MacBook Pro 13.3 mid 2012 - a1278 - no internal display

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