Re: Macbook 820-00840 no image, no backlight

I fixed the computer! I replaced the screen connector, and everything is good again. The resistance between PPVOUT_S0_LCDBKLT and EDP_INT_AUX_N was measuring 500kOhm before replacing the connector. After replacing the connector it was infinite resistance. So the decreased resistance was enough to interfere with communication or there was physical contact between the AUX pins due to the connector being burnt.

Re: Macbook 820-00840 no image, no backlight

Thanks for the tip. I measured diode and resistance on the CPU side of C8529 (EDP_AUXCH_C_N) and C8528 (EDP_AUXCH_C_P). Here are the results in a pseudo table.

[CODE] AUX_N AUX_P
Diode mode (red to ground) 0.256V 0.259V
Diode mode (black to ground) 0.289V 0.292V
Resistance (red to ground) 1.56k 1.56k
Resistance (black to ground) 10.1k 10.k[/CODE]

So the AUX channels don't appear to be shorted to ground.

Re: Macbook 820-00840 no image, no backlight

Well this board is just messing with me now. I hooked up all of the connectors including battery and the backlight came on with 44V at PPVOUT. Of course there was no image, and I couldn't get the backlight to come on again.

Re: Macbook 820-00840 no image, no backlight

I did clean the carbonized material with an ESD brush before first connecting the display, so perhaps that's why it worked at first.

What exactly should I be measuring between diode mode? Between both EDP_AUX and PPVOUT it is open circuit with 1mA that my DMM using. It's also open circuit between EDP_AUX and ground. I tried the probes the in both direction to make sure.

Re: Macbook 820-00840 no image, no backlight



I did a PRAM reset. It did not help, but I do have another problem that it won't post with J6951 connected; that may be due to connecting and disconnecting the battery though.

I can't measure the SMC_LID signals since they are on the bottom of board when I have to mount the board in the case. I am able to measure LID_OPEN, which is the ORed output of both SMC_LID signals, and it is high when the screen is open. Does that mean it doesn't recognize the screen?

I was able to measure EDP_PANEL_PWR_EN,...

I have an 820-00840 that has water damage. The corrosion was around the backlight driver, WiFI chip, inside the screen connector, and the BGA chip (PI3USB32) next to the USB port that doesn't show up on schematics. The board was initially stuck at 5V, but there were no shorts or obviously blown chips. After brushing the corrosion away from the PI3USB32 chip (no reflow yet), the board started taking 20V with peak 0.6A that settled to 0.3A. That seems normal from what I've found online.

I brushed the screen connector and checked the resistance between PPVOUT_S0_LCDBKLT and EDP_INT_AUX_N....

Re: New Members - please post your introductions here

Hello all,

New member here trying to fix a laptop for a friend. I have a background in electronics, but I don't work on computers.