a1502 820-4924-A Liquid Damage... no image, but boots when Magsafe plugged in

papalati

Member
Okay, so I wanna clear something up... you asked previously "When you start the board with internal LCD connected, check for voltage at R8320 pads."

Boardview shows R8320 as a 4 pin pad as I took a screenshot of, but when I look at the board it looks like pins 1 and 2 are a bridged pad to 3 and 4. Unless the 2 tiny pads above them are 3 and 4.

Please see comparison pics and let me know which letter is right. A or B.

I'm assuming A is right.
 

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2informaticos

Administrator
Staff member
R8320 is not placed on the board, so all 4 pads are tied together; for this reason I said "pads", not "pins".

No reason to replace Q7700, if BKLT_SD is not 0V.
Try known good full LCD assembly; must be from 2015.
 

papalati

Member
So what are the two small points above the pads that I marked 3 and 4 in image A?

Cause I don't have another panel to try. If I got the board working then I would've spent the money on another panel but if I can't get the board working then I'm not spending 300-400 on a good panel.

When I connected the good board before sending it back it showed the backlight and this one doesn't still so that means something is still wrong with this one.

I think I have to give up then at this point. :(
 

papalati

Member
I'm not sure if any of this matters...

r7750 = pin 2 = 0v

r7733 = pin 2 = 0v

how many volts should c8354 be? I’m only getting 1.47v
 

2informaticos

Administrator
Staff member
If you get 3V at DP_INT_HPD, internal LCD is detected and probably the image is there; but not visible on the cracked screen.
Until BKLT_SD gets 0V, you cannot get any voltage at D7710.
Do you still have 3V at BKLT_EN_R?

If you got backlight with another 4924 board on this LCD, then the problem is in the actual board.

"So what are the two small points above the pads that I marked 3 and 4 in image A?"
Are the pads for Kelvin connection lines of Isense, not used in this case; directly connected to pins 1 & 2 respectively.
 

papalati

Member
3.3v at DP_INT_HPD

BKLT_SD u7700 at Pin 11 = 12.4v
BKLT_SD R7702 at Pin 2 = 12.4v

No, I no longer have 3v at BKLT_EN_R. Now says 0v.
 

papalati

Member
u8300
1 = 0v
2 = 0v
3 = 5v
6 = 0v
7 = 5v
8 = 0v

u8310
1 = 0v
2 = 0v
3 = 0v
4= 0v


u8330
1 = 3.3v
2 = 0v
3 = 3.3v
4 = 0v
5 = 0v
6 = 3.3v
7 = 3.3v
8 = 0v
 

2informaticos

Administrator
Staff member
Please pay more atention wgen you work.
We need to be sure about all posted values.
Pins 1 & 3 of U8300 are tied together, like in schematic.

Do you really have 0V at all U8310 connections?
Pin 1/A1 is connected directly to 3V3_S0 (C8308)....
 

papalati

Member
Sorry about that. I thought I was making contact with the pins but it turns out I wasn't. Thought my probes were small enough as they are tiny but not tiny enough to fit underneath after all. Yes all the components around it are getting power. Need to find smaller probes.
 

2informaticos

Administrator
Staff member
Why try to make contact underneatch the chip?
Even on bigger QFN chips, you can easy make a short between pins.

ALWAYS measure touching the pins of surrounded components connected to the chip pin you want to test.
Use schematic/boardview to find proper test point.
 

papalati

Member
Okay. Gonna have to place an order for the connector. Any other ic's or other components that could be an issue that I should order just to be safe?
 
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