[SOLVED]A1502 820-3476-A USB on I/O board disabled

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nik1981

Member
Hi, I have a A1502 with 3476 (8GB) board that has has had liquid damage. Its been cleaned and now works apart from the right USB (I/O board) is being disabled due to too much draw. The left usb works fine, even when the right it disabled.
Keyboard and trackpad work fine. Trackpad had some liquid damage on one of the ribbons initially but that was cleaned off and it sorted the crazy cursor issue.

I've tried with keyboard and trackpad ribbons not connected and its the same.

I've tried another I/O board and ribbon connector with the same result.

If you plug in a mouse, you get a light but nothing more.

I've seen it once work fine for about 10 seconds after initial boot up, but then it was disabled by the OS
Any ideas as to what I should check would be really appreciated.
 

dukefawks

Administrator
Check voltages on R1580-83, those are the USB over current alerts to the CPU. One of them will probably be low. Check diode mode on the one that is low.
 

nik1981

Member
Thank you Duke,

R1580 is 3.28v on USB_EXTA, 3.33v on PP3v3 - 98.3kohm
R1583 is 3.21v on USB_EXTD, 3.33v on PP3v3, - 78.6kohm

Apart from the 78.6kohm on R1583, they look pretty okay, maybe 3.21v on R1583 is a bit low also.

What do you think?

Thanks again for helping, I hope I gave enough info.

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Diode test

R1580 is 0.420 on USB_EXTA
R1583 is 0.438 on USB_EXTD

Both resistors measure 0.301 on PP3v3 pins

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Last edited:

nik1981

Member
I took off R1583 with the intention of replacing it, but when its off the board, it has 99.8k resistance which it perfect really.
 

nik1981

Member
Found that pin 1 (USB_EXTB) on R1581 wasn't actually making contact, so removed that, cleaned the pads and replaced it. The right USB seems to be working now.

Those 0201 resistors aren't great to solder!
 
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