820-00165 - Short Hunting - No Display

sws

New member
Hello,

Working with an 820-00165 that has green light/orange light, fan spin, and boot chime but no display. Connecting to an external monitor works and the blinking folder shows up on the external monitor. F7700 has 8.57V on both sides but PPVIN_S0_SW_LCDBKLT at pin 1 of L7701 is 0V. PPVIN_S0SW_LCDBKLTFET going to pin 4 of Q7706 is 8.57V. BKL_EN at U7701 is 0V. PP5V_S0 at U7701 is 5.128V and PP3V3_S0 is 3.4V.

I'm thinking that there may be a short to ground based on getting a small tingle while resting my arm on the chassis and taking a measurement. The short might then be causing U7701 to not turn on the display. However, I can't find the short anywhere on the board. Nothing is extremely hot. Aside from measuring component to component, is there a good strategy for finding a short that would affect the display?

Steve
 

sws

New member
EDP_BKLT_EN is 0V and BKLT_PLT_RST_L is 3.338V. Looking at the schematic, both of these connect to Q7707 which then must decide whether to enable the backlight or not(?) From what I can tell, EDP_BKLT_EN is created by U0500 or am I reading that wrong?
 

2informaticos

Administrator
Staff member
Yeah, PCH sends out EDP_BKLT_EN.
Internal LCD is maybe not recognized; do you get image at least?
If not, no reason to search for backlight...

What about pins 14 & 18/19 of J8300?
 

sws

New member
I think the issue may have been found, thank you. In looking to measure the pins of J8300, I noticed that L8304 didn't look quite right. Under the microscope, it appears as though L8304 exploded. I cleaned up the surrounding area. C8315 is not looking so good either. I'm attaching a photo. L8304 is just to the left of center. I will be looking for a donor part or ordering a new L8304 soon.

Steve
 

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