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A2779 - 820-02841 - No image - U6070 troubleshooting

J

joesklar

New member
Hi there,

I'm trying to troubleshoot the U6070 circuit for this board. I have no image, but I know the LCD is good from testing on another laptop.

I have the following readings:

R6071
Pin 1: 12V
Pin 2: 3.2V

R6072
Pin 1: 3.2V
Pin 2: 0V

C6070
Pin 1: seems to fluctuate between 0V and 3.2V
Pin 2 0V

Q6070
Pin 1: 1.78V
Pin 2: 0V
Pin 3: 0V

Is in voltage in correct? I can't see any reference in the schematic for what the voltage should be.

Any help would be much appreciated. I'm attaching the boardview and schematic in this folder as it is too large to upload.
03 820-02841 SCHBRD - Copy.rar

Kind regards
 
2informaticos

2informaticos

Administrator
Staff member
What is the relation between image and U6070?

Any history available?
Did you test USB activity and external video?
 
J

joesklar

New member
Hi,

Sorry, I realise that was some crucial info I left out.

The history is a prior repair attempt. I found U6070 had loads of flux marks. I figure this is something to do with the fact that the video is not showing on internal screen.
USB is at 20V stable and fluctuating between 50 and 500mA.
System boots fully and outputs external video.

I have no chime or keyboard backlight. I think this is related to this missing P3V8AON_ISENSE_EXT, which could also be causing the no image issue.

Thanks
 
2informaticos

2informaticos

Administrator
Staff member
Seems that you don't understand what you are looking for.
Mentioned signal must be close to 0V; is related with the current consumption from 3V8_AON.

Did you check if JP600 gets correct power rails?
 
J

joesklar

New member
Yes I don't know everything, that's why I pay the forum membership ;).

JP600 has no power going to it. Power in via pins 37 & 38 "PP3V8_AWAKESW_TCON" from what I can tell this power is coming from UP710.

All readings taken with LCD connected.

PPDCIN_AON - 19.8V
PPBUS_AON - 12.3V
PP3V8_AON - 3.8V
PP5V_S2_MAIN - 5.1V
PP3V3_AON - 3.3V
PP5V_AON_P3V8AON - 5.0V
PP1V8_S2SW_SNS - 1.8V
PP1V2_AWAKESW_BLC - 1.2V
PPBCON_AWAKESW_BKLTCONN_VIN - 3.3V
PPMDB_AWAKESW_TCON - 0V
PP3V8_AWAKESW_TCON - 0V

UP710
PIN 1 PP1V8_AON - 1.8V
PIN 2 LCD_PWR_EN - 0V
PIN 3 PMU_SYS_ALIVE - 1.79V
PIN 4 EDP_PANEL_PWR_EN - 0V
PIN 11 EDP_PANEL_1V8_EN - 0V
PIN 13 EDP_BKLT_1V29_EN - 0V

LCD_PWR_EN coming from U8100. I don't like where this is going...
 
J

joesklar

New member
I think the readings I gave above the LCD connector must have been misalgined. I tested again and got the following:

UP710
PIN 1 PP1V8_AON - 1.79V
PIN 2 LCD_PWR_EN - 1.79V
PIN 3 PMU_SYS_ALIVE - 1.79V
PIN 4 EDP_PANEL_PWR_EN - 1.79V
PIN 11 EDP_PANEL_1V8_EN - 1.79V
PIN 13 EDP_BKLT_1V29_EN - 1.79V
PIN 10 EDP_PANEL_DISCHARGE - 0V

UP701
PIN 1 PP3V8_AON - 3.8V
PIN 2 LCD_PWR_EN - 1.8V
PIN 3 PP3V8_AON - 3.8V
PIN 5 (SCHEMATIC) - 0V

On closer inspection, there is a solder blob sticking from the underside of UP710. I will reflow and post readings again. I assume that EDP_PANEL_DISCHARGE must be live for QP700 to output and in turn power PPMDB_AWAKESW_TCON.
 
2informaticos

2informaticos

Administrator
Staff member
Don't touch UP710 yet.
You may have bad UP701; it should deliver output voltage.
Check first diode mode at its output; w/ and w/o LCD connected.
 
J

joesklar

New member
Hi,

I replaced UP701 as advised, but still no voltage. All readings remain as prior to swap.

Pretty sure QP700 is an en N-channel, so it wants voltage on the gate to turn on. Because pin 10 (EDP_PANEL_DISCHARGE) of UP710 is 0V, it is not switching...

What are your thoughts?

Thanks
 
2informaticos

2informaticos

Administrator
Staff member
Why would you want to enable QP700?
Do you know what DISCHARGE means???

Check if UP701 delivers output voltage with screen disconnected; at least in the first seconds, when machine chimes.
 
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