820-02098 - A2242 - No image

[joesklar]

Hi everyone, new member here.

I've worked on older Apple devices in the past, but have only worked on a few of the newer devices. I'm a hobbyist and not fixing any of these devices for a customer base. I've bought a few devices recently (M1, M2 Pros mainly) with various board faults.

This particular laptop boots, chimes etc. There is no image, backlight, or external monitor output.

This was reported as liquid damaged, but there's no obvious problem areas on the board. I notice that UP800 has no output (tested on LP800), but I guess this is due to no image?
The display connector(s) all look to be pristine. I was trying to test voltages on JP600 but could only verify pin 4 as present. Not sure where the best test points are when the screen is connected. Is there a table anywhere for nominal diode mode readings? Or am I jumping the gun and should be checking other areas first?

Any help would be much appreciated!

Kind regards

 

[2informaticos]

First of all, welcome to the forum!

All image and backlight signals MUST be checked with LCD connected, so isn't an easy job.
You should try to find test points using schematic/boardview.

Find and check corresponding points for pins 4, 32, 34, 38.

BTW, did you test external video disconnecting JP600?

 

[joesklar]

Good morning, and many thanks for the welcome.

I tested the external video with JP600 disconnected. Still no output.

Just for my understanding, when you say the LCD should be connected for all signal checks, does this include diode mode readings?

I removed the antena bar so that I'd have more movement in the flex cables to do testing. I found that the cable connecting to J400 has a hard crease/fold in it. I imagine this is a botched prior screen replacement attempt. It may be the source of the issues?

Pins 32 and 34 connect only to a small BGA chip and the SOC. How can I test these?
Pin 38 is supposed to connect to RD892, but there is no component there. Is that normal?

I've attached a PDF of my findings here

Thanks for your help so far!

 

[2informaticos]

For diode mode readings, you can check in both cases, w/ and w/o LCD connected.
You can get more information, comparing the readings.

You should test with known good LCD assembly.

 

[joesklar]

Hi,

I don't have a known good assembly at the moment. I do have a A2779 though. Do you know if the display assemblies are interchangable?

Thanks

 

[2informaticos]

Yes, you can use it for test.

 

[joesklar]

Ok I swapped the display. One step foward, and two back. I have an image now. Apple logo, but no backlight and it is power cycling by itself every 30 seconds or so. Initially I had a chime with the boot loop, but that has stopped too.

 

[joesklar]

The screen from this laptop (A2442) also does not work on the A2779. So I'm happy that this screen is cooked.
What I'm unsure about is, will buying a replacement LCD fix the issue? I'm concerned that there is no video output. Should there be video output when the screen is disconnected? For info I have only tested via HDMI. I don't have a USB-C monitor.

 

[2informaticos]

You should get HDMI output w/ or w/o internal LCD connected.
But sometime, external video appears later, if internal is still connected.
The problem is that you are not sure if HDMI output is OK.
Should test with USB-C adapter to discard such issue.

I didn't swipe screens for M1 and M2 machines.
Someone told me that he swipped screens between working M3 machines (identical) and didn't get backlight.
You may have problems with MLB backlight circuit, but should test with proper screen; to avoid any incompatibility issue.

 

[joesklar]

Hi,

Okay understood. I will order a USB-C adapter and a replacement LCD. Will post back when I know more.

Many thanks

 

[joesklar]

Quick update, the laptop works with external display output on the USB-C adapter.
I have the LCD on order as well. Fingers crossed that fixes the issues. If not hopefully the backlight circuit and HDMI out are simple enough to resolve.