A1502 screen only issues

[aazjo]

I have a MBP A1502 (early 2015, 820-4924) with a screen that will not turn on. I have swapped screens with a cracked test screen and the computer boots and the cracked screen works for both backlight and image. The black/blank screen appears to do nothing.

I have collected resistant data from the cracked screen connector pins and submitted to OBData server:

1 PPVOUT_SO_LCDBKLT OL
3 I2C_BKLT_SCL 9.97M
4 I2C_BKLT_SDA 9.89M
5 PP3V3_S0_EDP_R 79.10k
6 SMBUS_SMC_0_S0_SCL 321k
7 SMBUS_SMC_0_S0_SDA 323k
8 EDP_BKLT_PWM 99k
9 LCD_HPD_CONN 101.5k
10 LCD_IRQ_L 7.94M
11 DP_INT_AUX_P 1M
12 DP_INT_AUX_N 1M
28-30 PP5VR3V3_SW_LCD 7.19k

Testing the black/blank screen I get similar results, but slightly lower values.

I have tested PPVOUT_S0_LCDBKLT when powering on the computer with the black/blink screen attached and get 0V. Attaching the cracked working screen I get 39.3V. I have swapped LVDS/eDP cables between the screens with no difference, so both cables appear to be good. Disconnecting the screen cable and plugging into HDMI also works perfectly.

What else can I test on this seemingly perfect black/blank screen before giving up on it? I have an adaptive backlight tester that I have used for TV backlight and other older laptop backlight circuits, but I don't know how these newer eDP screens work with their PWM inputs and if that tester would short something else out. If I was to use it I would think that I would put positive on PPVOUT_S0_LCDBKLT and negative on any of the GND pins. Please let me know what you think and/or if this screen is salvageable in any way.

[mon2]

Re: A1502 screen only issues

1) What is the history on the replacement black screen ? Is it known to be 100% compatible with this logic board model ? Does it work on other A1502 logic boards?

2) meter in voltage mode. what is the voltage of PP5VR3V3_SW_LCD @ L8300, pin # 2 ? This is the power rail for the LCD.

a) check the voltage without any LCD connected.

b) check the voltage with the black screen connected. The voltage on this rail should match the value of the cracked but working lcd. If not, that is a hint that the display is not of the same pinout as the original cracked display.

3) On the same logic, check and post the voltages for the I2C bus interface lines that mate with the LCD display to extract the display ID.

I2C_BKLT_SCL
I2C_BKLT_SDA

Compare to the voltages on the working, cracked display. Expecting these lines to be close to +3v3 for the working LCD display = I2C bus is open drain and the pull-up resistors on the I2C line will pull these lines to a 'soft high' state.

[aazjo]

Re: A1502 screen only issues

1. It have purchased multiple A1502s from Ebay, so I don't really know the histories of them. But when I opened the latest two, they seemed incredibly clean and didn't appear to have been worked on previously. I have tried the black/blank screen with other 4924 & 3476 boards and it has the same behavior, does nothing. Since I had the cluch cover off on them I took a look at the part numbers and compared them to other known good screens, here is what I found:

Part#, Screen Description
LSN133DL03-A03, cracked screen that works with 4924 (2015) boards. Date code 20151203
LP133WQ2(SJ)(A1), blank screen that I've been trying to troubleshoot. No date code
LP133WQ1(SJ)(E1), known-good screen that works with 3476 (2014) board.
LSN133DL03-A04, known-good screen that works with 4924 (2015) boards. Date code 20151008

Since the part numbers of the blank screen and my known-good 2014 screen are both similar, I will conclude that they are for the same type of 3476 boards. I tested the blank screen with my 3476 and it was still blank, no change to its behavior. I think I can conclude that it is failed, someone swapped it out for the 2015 screen that should have been with the working board, and perhaps something is shorted out on the inside according to the reading that I got below.

2a. PP5VR3V3_SW_LCD is reading 5.13V on my 4924 board without the LCD connected, but then drops to 0V shortly afterwards. I'm assuming this is normal behavior when it detects that the LCD is not connected.

2b. I tested all of the pins on J8300 with both screens hooked up. Last reading is the cracked screen and the first reading is the blank screen (colon separated).
1 PPVOUT_SO_LCDBKLT 0V : 39.3V
3 I2C_BKLT_SCL 5.13V : 5.08V
4 I2C_BKLT_SDA 5.13V : 5.07V
5 PP3V3_S0_EDP_R 0.0mv : 3.32V
6 SMBUS_SMC_0_S0_SCL 0.0mv : 3.30V
7 SMBUS_SMC_0_S0_SDA 0.0mv : 3.30V
8 EDP_BKLT_PWM 0.7mv : 2.19V
9 LCD_HPD_CONN jumps to 1.89V then back to 0.0mv : 3.29V
10 LCD_IRQ_L 0.2mv : 3.19V
11 DP_INT_AUX_P 0.0mv : 1.6mv
12 DP_INT_AUX_N 0.0mv : 1.6mv
28-30 PP5VR3V3_SW_LCD 0.0mv : 5.11V

3. See above readings.