820-01814-01 Macbook Pro A1990 with short

[carlucci]

Hi all.
I have here a Macbook Pro that already as been in another tech and came with a short in ppbus_g3h.
the board model is 820-01814-01, I already have the schematic and boardview.
A need guidance here, like where to start cheking.
Thank you.

[mon2]

Re: 820-01814-01 Macbook Pro A1990 with short

hi.

1) PPBUS_G3H is created by U7000.

2) Remove all power. Meter in ohms mode (resistance). Check the resistance to ground on F7000 (fuse), pin # 2. Value in ohms ?

Assuming the reading is low - then you have a short on this rail or a bad cap which will show similar results.

3) Remove F7000 & F7001 (if present) and repeat the reading on F7000, pin # 2. Value in ohms ?

4) With F7000 & F7001 OFF the logic board, power up and check if you see the PPBUS_G3H rail at the proper value @ F7000 pad, pin # 1 ?

This test is without F7000 installed.

Just wanting to confirm that U7000 and local mosfets are working ok.

[carlucci]

Re: 820-01814-01 Macbook Pro A1990 with short

Hi.
Resistance to ground on F7000 pin #2 is 00.3 ohms
After removing F7000 & F7001 pin 2# is 00.3 ohms
Powering the board gives me 12.23v in F7000 pad in pin1.

[mon2]

Re: 820-01814-01 Macbook Pro A1990 with short

So you definitely have a short on this rail. Good to see the PPBUS_G3H working ok.

1) Any liquid damage ? Any corrosion ? Any parts that look like they have been played with?

2) You either have a hacked up (bad soldering) logic board where there are solder shorts and causing this issue. Or you may have a bad cap that is causing this event.

Do not recommend injecting of a power supply from your lab till we know more about this logic board.

Search around where you may find where the last tech was - that area needs to be carefully reviewed for the short. If nothing is found, only then should you consider to inject an external voltage rail of perhaps 1v0 and check the current draw. The idea is that the shorted part will heat up and self destruct - hoping it will be a bad cap.

As noted above, search for bad soldered parts first from the last tech.

For assistance, remove fuse @ F8400. Just for now. Does this short disappear ? This fuse is linked to the backlight regulator.

If the short does not get removed, solder fuse F8400 back onto the logic board.

More ideas to try (to locate the PPBUS_G3H short):

1) remove the trackpad cable or remove fuse F6700. Check for the short condition again.

2) Assuming that the last tech was not a hack and did not short out pads with their soldering...review each polarized cap that is mated with the PPBUS_G3H rail. In the PDF schematic, search for "PPBUS_G3H". Once you find a block of bulk caps, review each for possible visible damage / color change on the body of the part. If you suspect it, carefully remove the bulk cap.

Post back on the condition of your logic board and hope you can use an external power supply to inject power and alcohol to hunt down the bad cap.

Would you have an external power supply and alcohol? We have used this method to fix a number of bad cap logic boards very quickly.

[carlucci]

Re: 820-01814-01 Macbook Pro A1990 with short

Hi, yes I have power supply and iso alcohol. Tomorrow I will follow your tips and will send you the feedback later. Thank you very much.

[carlucci]

Re: 820-01814-01 Macbook Pro A1990 with short

I forgot to tell you, after I remove F7000 and F7001 I saw "light red" spots in the board, so, liquid damage areas.

[dellxps15]

Re: 820-01814-01 Macbook Pro A1990 with short

post picture of red dot zone.

[carlucci]

Re: 820-01814-01 Macbook Pro A1990 with short

pictures attached.

[dellxps15]

Re: 820-01814-01 Macbook Pro A1990 with short

red spot looks like ripped of component, while green spot looks like desoldered component.

remove fuse f7001 f7002 and solder one wire to pin 2. use lab psu and try with 1 volt and see if something get hot.

[SMDFlea]

Re: 820-01814-01 Macbook Pro A1990 with short

red spot looks like ripped of component, while green spot looks like desoldered component.

remove fuse f7001 f7002 and solder one wire to pin 2. use lab psu and try with 1 volt and see if something get hot.

The red spot i think is the moisture sticker.Its white,then turns red with liquid damage,invalidating any warranty. When he said "light red" spots in the board" he might have meant sparks ? don`t know .

[carlucci]

Re: 820-01814-01 Macbook Pro A1990 with short

Yes it's the sticker that turn's red with liquid damage. Tomorrow I will give you the feedback of your tips, Thank you very much.

[dellxps15]

Re: 820-01814-01 Macbook Pro A1990 with short

yes i was meaning red and green zone in my modified pictures

1 red and one green for esch side of the board

[carlucci]

Re: 820-01814-01 Macbook Pro A1990 with short

Hi Guys! sorry my delay. I'm away and will be back in first week of july, please do not close this thread. Thank you.

[carlucci]

Re: 820-01814-01 Macbook Pro A1990 with short

Hello guys, for the sake of respect for everyone, I owe an explanation, I could not return to this subject because in the meantime I was hospitalized with COVID and I am still recovering from all this, I predict to return to active duty in November. Thank you.