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820-3115-B No Boot

S

sangolossyfon

Member
Board symptoms- Fan runs max speed when plugged in no matter what. But no backlight or display, no activity when USB is plugged in, even in SMC bypass. All S5-S0 5V and 3.3V rails are good so suspecting CPU failure. This one had no sign of life at all until I replaced C1768 which had broken loose from the board and now it just spins the fan. G3H voltage 13.22V, PP5VS0 5.23V, P3V3S0 3.51V. Draws 18W from wall.
 
S

sangolossyfon

Member
I actually re-measured CPU core voltage and the PLT and they were 1.15v and 3.3v respectively. While USB ports do get power there is no usb activity.
Coils-
L7030- 13.5/14v
L7630- 1.1/7.5v
L7100- 0.8/1v
L9701- 2.5/3.5v
L7520- 8.8/1.1v
L7510- 4.4/1.1v
L7260- 5.4/6.4v
L7220- 3.5/3.8v
L7330- 1.6/1.6v
Only coil with 0v was 7550, 0v on both sides.
The cpu does get a bit warm.
 
2informaticos

2informaticos

Administrator
Staff member
CPU core should drop from 1.1V to 0.7V aprox, when board boots.
There may be a communication problem between PCH, CPU and BIOS.

BTW, stop checking DC voltage on any coil's input pin.
 
S

sangolossyfon

Member
Yes it just stays at 1.17v. Does the same in SMC bypass mode. Also I will say that the fan does spin up slowly to full speed, if I put it in SMC bypass mode the fan gets to max speed much more quickly. CPU and PCH both do get hot. 19.5w draw from wall so this makes sense.

Could the 0 volts on L7550 be indicative of an issue?
Also, could the broken (one end was broken off) C1768 have caused any other parts of the board to fail? It does supply power to CPU.
 
2informaticos

2informaticos

Administrator
Staff member
"Could the 0 volts on L7550 be indicative of an issue?"
I already mentioned on other post, this board doesn't get iGPU core voltage on boot!
It is enabled only when hard graphics load is detected.
 
2informaticos

2informaticos

Administrator
Staff member
"There may be a communication problem between PCH, CPU and BIOS"
Check all SPI BUs Series Termination resistors and all their traces/solders.
Try flashing known good BIOS.
Check all PCH's voltages from page 22; there may be open series resistor, or coil.

Last options, reflow PCH and CPU; to burn eventually accumulated crap underneath.
 
S

sangolossyfon

Member
NO problems with the resistors that I can see and they all matched their correct ohm values.
Tried replacing BIOS chip to no avail.
Tried reflowing CPU and PCH
so i'm giving up on this one unfortunately. On to the next!
 
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