Preamble: Not water damage. Suddenly black screen during use, can't turn on afterward.
This is my first chip-level laptop repairing.
Detail diagnosis: AC LED on, battery charge normal. Power LED on but no display and no error LED blinks. Long press power button can turn off the power LED. When no RAM, power LED is keeping on and all know voltage is present(detail is as below). When RAM is installed, no display, all voltage measured but the power self turns off after 30 sec.
Voltage measured:
V19: 19.7V
3VALW: 3.36V
5VS: 5.02V
3VS: 3.36V
V2P5: 2.57V **
V1P8: 1.82V
V1P2: 1.24V
V1P05: 1.05
VNN: 1.02V
VCGI: 0.72V
VDDQ: 1.2
VMemory: 1.2V
VTT: 0.6V
Basically, all LDO or DC-DC can be measured with the correct output. The above V2P5 is just a guess from the label (broad label PU2501), Gemini-Lake does not define this power rail.
While on, measure with an oscilloscope: 19.2M/32.768K oscillate, G781 temperature IC reports <35C. LCDVDD low seems epd_vdden is low (since no schematic is available, it is just a guess from a similar schematic of LA-G07EP)
Tried cleaning original bios, same symptom. Tried HP stock bios without any modification, 5.3 blinks.
Conclusion:
POST fails at VGA initialization with a timeout. Possible faults from 1) fried CPU, 2) support circuit for display, or 3) RAM. Since I don't have another RAM module to verify, I wish to rule out 1) and 2) first.
Any suggestion on further diagnosis??
This is my first chip-level laptop repairing.
Detail diagnosis: AC LED on, battery charge normal. Power LED on but no display and no error LED blinks. Long press power button can turn off the power LED. When no RAM, power LED is keeping on and all know voltage is present(detail is as below). When RAM is installed, no display, all voltage measured but the power self turns off after 30 sec.
Voltage measured:
V19: 19.7V
3VALW: 3.36V
5VS: 5.02V
3VS: 3.36V
V2P5: 2.57V **
V1P8: 1.82V
V1P2: 1.24V
V1P05: 1.05
VNN: 1.02V
VCGI: 0.72V
VDDQ: 1.2
VMemory: 1.2V
VTT: 0.6V
Basically, all LDO or DC-DC can be measured with the correct output. The above V2P5 is just a guess from the label (broad label PU2501), Gemini-Lake does not define this power rail.
While on, measure with an oscilloscope: 19.2M/32.768K oscillate, G781 temperature IC reports <35C. LCDVDD low seems epd_vdden is low (since no schematic is available, it is just a guess from a similar schematic of LA-G07EP)
Tried cleaning original bios, same symptom. Tried HP stock bios without any modification, 5.3 blinks.
Conclusion:
POST fails at VGA initialization with a timeout. Possible faults from 1) fried CPU, 2) support circuit for display, or 3) RAM. Since I don't have another RAM module to verify, I wish to rule out 1) and 2) first.
Any suggestion on further diagnosis??
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