(Solved) 820-00840-A logic board. Short on both USBC ports.

[joshAU]

Hi all.
Had a customer bring in this A1708 Macbook Pro reporting that neither USBC port worked.
I thought they had easily replaceable USBC ports, so I ordered one in...only to find that its an unusual setup directly soldered to the logic board.

I cleaned the connectors and tested - and wow, they sure get hot very quickly.
I'm guessing a short circuit on both ports.

I'm getting 2.4 ohms resistance to ground onPP20V_USBC_XA_VBUS, measured at pin1 of C3303.
Not a complete short but lower than I assume it should be.

Not familiar with this model at all unfortunately, nor have I worked on USBC circuits before, so any advice greatly appreciated.

 

[2informaticos]

So you have original USB connector still in place?
Remove F3000/10 and check if still short.
If short remains before the fuses (on the connector side), D3300/400 are the first suspects...

 

[joshAU]

Hi 2informaticos.
No, I still haven't removed the original connector.
I removed both fuses and tested.
On both fuses, on pin1 they both show 2.4 ohms.
Pin2 no short.

I removed D3300, then D3400, and pin1 is still showing 2.5 ohms.
Measuring D3300 and D3400, while removed froim the board, with red on the larger pad (pin1) and black on pin2, they both show approximately 111 ohms. The other way they both measure over 200K ohms.
So I guess they are OK?

WIth both D3300 and D3400 removed, pin1 of the diodes show directly connected to ground (zero ohms), where as pin2 show 2.4ohms.

And gee aren't they fragile, lol?
I managed to shatter one with just the pressure of the tweezers.

Having a close look at j3000, one the USBC connectors, there appears to be some damage that is shorting it out through J3300.
What do you think?
The first one is on the connector that is the highest, when looking at the top side in boardview, and on the top side.
The second one is on the connector that is the lowest, when looking at the top side in boardview, and is on the bottom side.

Is it very hard to solder one of these J3300, new if available, or from a donor board?

 

[2informaticos]

You must change the port, is clearly damaged.
I only changed from donor board.
Not so difficult to solder it.
Use 138 degrees solder paste to desolder; better to use 58 degrees ChipQuik alloy.

 

[joshAU]

Thanks 2informaticos.
OK.... I'll give it a shot.

I've never really used solder paste to desolder anything....
I've already removed the heat shield from the bottom side of the board.

Should I be covering the 50+ pins under the heat shield on the bottom side of the board with 138 degrees solder paste?
And heat from that side as well?
Is that the correct way to approach it?

I do not have any 58 degrees ChipQuik alloy.

Thanks again for your help.

 

[joshAU]

Hmm, I don't think I have a board amongst my dead parts.... damn.
Had a look at that online auction site - one seller is selling them "refurbished" for $90 USD plus $30 international shipping, lol.
I think I'll pass at that price.

 

[joshAU]

Correction.... I found a dead board that matches....

 

[joshAU]

OK, fixed.
Thanks again 2informaticos.
You were right, once again - it was the USB ports themselves that were shorted.
I managed to desolder one from the ONLY matching board I had.

It was relatively straight forward, until I accidentally desoldered two tiny diodes right near by, while cleaning out all the pin holes.
They were not fun to reattach.

All good now, charging on both ports, detecting USB devices on both ports.
Thanks again.