820-1700-a Begin Troubleshooting and Board View quetsions

1337GameDev

New member
I currently bought a broken macbook (A2141), that was water damaged, and want to repair it. I have the necessary tools I've amassed over time, but want to begin. I have decent understanding of electronics and the like (I have watched a bunch of videos of repairs, as well as am a professional programmer as my career). I have the board out of the machine, and have organized the screws based on location they came out of and other covers / pieces.

The board has some obvious water damage. I know i'll likely need to source a donor board (i know that can be tricky to source, but i'll worry about that a bit later), but the first part is identifying the damaged components, organizing them / their location on the patient board and ensuring the board doesn't have an "unfixible" component (cpu, ram, ssd, gpu, t2, etc). I have removed the covers on top of these chips, and do not see corrosion near / on these chips. I do not see damage to the LCD connecter, so no 50v should be sent to the cpu / cpu mux. I will likely need to verify this however. I know i'll likely apply conformal coating to this area/other areas for future durability if I fix the board.

My questions are these:

1. What's the first steps to verify the CPU, gpu, ssd, t2, etc aren't going to be damaged if I connect this board to power? I know i should look for obv shorts, but what about verifying that power regulation systems for these won't generate too much voltage? Do I "isolate" these systems by removing caps / chips to ensure any generated voltage won't go to the chips in question and then add back the chips/components once they are checked?

2. What can be done to use a usbc amp-meter to current limit to ensure the board won't short and push a bunch of amps to a valuable chip? I do have a bench current limiting power supply, so i know i can inject voltage and bypass the usage of the amp-meter, just curious on thoughts.

3. On the board view, I tried finding and noting areas of water damage and understanding the circuits impacted, but the board view doesn't line up exactly with the board. I see corrosion around the L7660 area it seems (lower left of the board with the orientation it came out of the machine with the fans up at the top), to the left (close to C6566) on the board view, but there's also a connecter here (my best guess is J6500), that doesn't show up on the board view. So I'm having a hard time identifying components exactly to know if I'm getting a proper ID of components. Is there sub-variants of this board? What are tricks to "orient" or identify components that might be tricky to find on the board vs board view? Are the prefix letters indicative of the component type? (c= capacitor, r = resistor, I = inductor, U = chip, J = connector, etc). I do see an "L" prefix, but not sure what that corresponds to. Ideas / info?

4. What's the best surface to use a hot air station on (well what the motherboard will be sitting on when heating)? I wanted to do this in my living room (and put down a silicon mat to protect the wooden coffee table that states it can handle 400c) and have the fume extractor / camera there. I know not the "best" but i've done work like that before with little issue (i've taken apart hundreds of devices like that). I've heard people say silicon mats, as well as tile, and then things like specializes welder mats or the like.

5. I don't have a sonic cleaner ($1200+ for a basic one). I plan to clean using a toothbrush + alcohol (i know this will take awhile and be annoying / not as good as a sonic clean -- but it's what i have right now). Any ideas / tips / info I need to know when doing this to improve success / durability?

I sourced my board view online, from the "badcaps" forum (has filename of "LB_820-01700_BoardView_file_LO25.brd".) Is this incorrect or for a different variant? The macbook I have is an i7 configured 2019 16inch model ().

Is there any ideas / steps / info I need to know about this board specifically, and is there public collections of diode mode readings to help not needing a donor for comparison (while I look around to source one for a reasonable price)?

Sorry if this info can be googled, I figured i'd ask here to see what info you guys trust and what info you all have to share / help if possible, as there can be conflicting info out there. If you have links you know are good / trust, you can share those too versus just explaining (I understand I'm asking a lot). Thanks for helping! Much appreciated, and hopefully these questions help out others too who are working on their first board.

UPDATE:

On #3, I found a table for schematic prefixes:


L is inductor, and J is a connecter / jack.

I is not used afaik.
 
Last edited:

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

I have to mention that forum goal is to help in a repair process.
General information can be find here too, but if you are interested in personal training, should contact Rossmann staff.

Once you got a machine to repair, you can be sure it was already powered up in the state you've got it.
So, in theory, cannot cause more damage if you power it up, for test.
However, if the board is accessible, start checking for short, or low resistance to ground, on the power rails, like fuses and big coils.
Be sure to disconnect battery first.

If nothing strange detected, you can connect USB-C charger.
Be aware of injecting voltage on the board.
We explained many times on the forum how and when to do it.
Is even more important to understand when NOT do it.

Getting boardview and schematic for all revisions of Apple boards is impossible.
Sometime need to confirm circuits configuration checking continuity between some components, trying to identify what is there; based on schematic however.

Many people think an ultrasonic cleaner repair boards by itself; that's a big error.
Incorrect use of it, can cause more damage on the boards.
If doesn't have sweep function, or is not used, hot spots can appear and break traces, or knock off components.
Never use it to clean small areas.
It's use is more suitable when we expect accumulated crap under BGA chips, or the board is affected by corrosion in large areas and difficult access.

You can find many diode mode and voltage readings on Internet.
A very good webpage here:

This may be the same boardview as you've got, just compare it.
 

1337GameDev

New member
First of all, welcome to the forum!

I have to mention that forum goal is to help in a repair process.
General information can be find here too, but if you are interested in personal training, should contact Rossmann staff.

Once you got a machine to repair, you can be sure it was already powered up in the state you've got it.
So, in theory, cannot cause more damage if you power it up, for test.
However, if the board is accessible, start checking for short, or low resistance to ground, on the power rails, like fuses and big coils.
Be sure to disconnect battery first.

If nothing strange detected, you can connect USB-C charger.
Be aware of injecting voltage on the board.
We explained many times on the forum how and when to do it.
Is even more important to understand when NOT do it.

Getting boardview and schematic for all revisions of Apple boards is impossible.
Sometime need to confirm circuits configuration checking continuity between some components, trying to identify what is there; based on schematic however.

Many people think an ultrasonic cleaner repair boards by itself; that's a big error.
Incorrect use of it, can cause more damage on the boards.
If doesn't have sweep function, or is not used, hot spots can appear and break traces, or knock off components.
Never use it to clean small areas.
It's use is more suitable when we expect accumulated crap under BGA chips, or the board is affected by corrosion in large areas and difficult access.

You can find many diode mode and voltage readings on Internet.
A very good webpage here:

This may be the same boardview as you've got, just compare it.

Well, ive watched a LOT of rossmann repair videos over the past few years, and learned a lot on electronic engineering and such.

I distinctly remember videos where Louis started checking to ensure the CPU / GPU didn't have any issues that'd kill it when powered up. So I know it's a considering, I just wanted to cover this base before powering it up.

And what do you mean "nothing strange?" There very likely is a short on PPBUS_G3H, or other main power rails (as there is no power), and i'll need to fix this before even attempting to power up the board?

And yeah, i know that schematics are hard to find, but I am assuming the schematic is correct, as I feel there is only one board with model 820-1700-A, but every model might not have a schematic.

And yeah, i understand the sonic cleaner thing, where people use it as a crutch. I would only use it to remove flux / random debris after the board is working.

I'll give that logi wiki a read over, as well as perusing the forums for people with this board.

One other question, are SMD components usually interchangeable if I get a different board from the same year? I know the ssd, t2, gpu, ram, cpu, etc might be different, but curious if a board from a different model can be used as a donor for SMD caps, coils, resisters, general use chips, etc after I identify damaged components? I figure there might be differences in tolerances after I look at schematics and compare the SMD component values for coils, resisters, caps, etc.

Is it also common to have board is the same / years near this board for similar circuits, to use as reference / understanding / comparing diode readings?
 

2informaticos

Administrator
Staff member
No power doesn't mean short.
Many different things can cause no power!

"Nothing strange" I mean no short, nor low resistance to ground on a power rail.

I didn't say to power up the board as is.
I just explained, that can't be very risky, as it was already done several times by client.
Once the machine is open and have access to the board, any reason to power it before checking in diode mode first?

Using donor boards for the same model is important when you search for chips with internal firmware.
Passive components don't suppose any complication, apart of finding correct value and size.
Also active components, like diodes and transistors can be taken from different boards.

Please, write directly into Reply box, instead of clicking Reply button.
Unless you see a reason to quote an entire post, visible few centimeters above.
We try to maintain forum aesthetic, thanks.
 

1337GameDev

New member
Looking at the board, im curious if some components are interchangeable. The 820-1700-A board is still really expensive as a donor, and I'm curious if the 820-01598 board (2019 13in macbook pro) has interchangeable components. Particularly the "U8400 (lcd backlight TI dc->dc boost converter)" on each board: "LP8548B1SQ_-04 (LLP)" on the 13in board, vs the "LP8548B1SQX06 (WQFN)". I am assuming WQFN is the package size for this IC, but i'm unsure what LLP means (googling gives no results). The pinouts of these are the same, and in the same order/orientation on the schematic.

I will likely be encountering this a lot, as it seems apple schematics are "slightly" different between models, even if some components could be interchangeable due to oddities.

Just comparing and verifying so i can plan on a donor board as i test components / rails for issues.
 

2informaticos

Administrator
Staff member
As I said, circuits from different boards can be used, if no specific board firmware is involved.
Backlight IC is not suspected to cause such problem, so you can replace it.

Sometime we don't have any information and just need to try and see what happens.
 
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