I posted about this earlier, but I've made some progress and I have more specific questions.
This is a Lenovo G580 Model 20157 with a LG4858 UMA MB. The MB part number is 48.4SG16.011.
The original symptoms were: Power button -> fan turns on, webcam light turns on, no gfx core voltage or video output, caps lock doesn't work. Eventually the fans stop and go again before the board powers down.
So I rigged up an Arduino Due as an SPI EEPROM programmer and flashed a factory bios (I think?) to the U6001 which is a Winbond W25Q64. Upon rebooting, the screen went white and now the board responds to keyboard input. 800mV on the gfx core rail.
All signs point to this thing actually booting. I can play with the bios settings blind--F10 followed by enter (save and restart in the bios) causes the board to reboot. A disk with Windows on it will boot but with no video! I don't have another screen to test with, unfortunately.
Anyway, I found that U4901 (a switch that uses LVDS_VDD_EN to conduct 3.3V to LCDVDD) was getting flesh-burning hot. LCDVDD was fluctuating wildly around 200mV, probably the U4901 thermal protection cutting in and out. Unplugging the LCD connector and removing the bypass caps on that rail didn't change this. So I removed U4901 and shorted 3.3V to LCDVDD through a multimeter on the current setting. The screen went from white to black with 150mA flowing. Colored and backlit black, not screen off black. Still no signs of functioning video.
My question is what does U4901 actually do? Can I just leave it shorted? It's a SY6288 "Low Loss Power Distribution Switch" with over-current and thermal protection. I read that for LCD screens in general, you control screen contrast by changing another voltage in relation to VDD. But I suppose you could also do it the other way around. Is this chip just used as an on-off switch with protection for the 3v3 rail or is it supposed to actively modulate the 3.3V input to the screen? The input signal LVDS_VDD_EN suggests it's just acting as a switch but I'm not sure.
I need to get another screen to see if I have video problems further upstream. It could also be that the bios is still wrong. If you have bios advice please let me know.
It is not the processor. I have an identical processor and swapping it doesn't change anything.
Thanks for reading! I do have a new motherboard on the way, but since I've seen two G580s with this exact problem, I feel some need to fix this particular board and post about it so as to help others.
This is a Lenovo G580 Model 20157 with a LG4858 UMA MB. The MB part number is 48.4SG16.011.
The original symptoms were: Power button -> fan turns on, webcam light turns on, no gfx core voltage or video output, caps lock doesn't work. Eventually the fans stop and go again before the board powers down.
So I rigged up an Arduino Due as an SPI EEPROM programmer and flashed a factory bios (I think?) to the U6001 which is a Winbond W25Q64. Upon rebooting, the screen went white and now the board responds to keyboard input. 800mV on the gfx core rail.
All signs point to this thing actually booting. I can play with the bios settings blind--F10 followed by enter (save and restart in the bios) causes the board to reboot. A disk with Windows on it will boot but with no video! I don't have another screen to test with, unfortunately.Anyway, I found that U4901 (a switch that uses LVDS_VDD_EN to conduct 3.3V to LCDVDD) was getting flesh-burning hot. LCDVDD was fluctuating wildly around 200mV, probably the U4901 thermal protection cutting in and out. Unplugging the LCD connector and removing the bypass caps on that rail didn't change this. So I removed U4901 and shorted 3.3V to LCDVDD through a multimeter on the current setting. The screen went from white to black with 150mA flowing. Colored and backlit black, not screen off black. Still no signs of functioning video.
My question is what does U4901 actually do? Can I just leave it shorted? It's a SY6288 "Low Loss Power Distribution Switch" with over-current and thermal protection. I read that for LCD screens in general, you control screen contrast by changing another voltage in relation to VDD. But I suppose you could also do it the other way around. Is this chip just used as an on-off switch with protection for the 3v3 rail or is it supposed to actively modulate the 3.3V input to the screen? The input signal LVDS_VDD_EN suggests it's just acting as a switch but I'm not sure.
I need to get another screen to see if I have video problems further upstream. It could also be that the bios is still wrong. If you have bios advice please let me know.
It is not the processor. I have an identical processor and swapping it doesn't change anything.
Thanks for reading! I do have a new motherboard on the way, but since I've seen two G580s with this exact problem, I feel some need to fix this particular board and post about it so as to help others.
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