X550CC no PWM for +VGFX_CORE

[paulo66]

Asus K550C - X550CC_V2 MB turns ON, no image.
Now, the power sequence tests fine except for the last step: +VGFX_CORE is absent. The controller is not sending the PWM signals for the upper and lower MOSFETs. So, what else is necessary to trigger those PWMs?

One other fault: the fan starts spinningupon power up, but after a while it speeds up and down as if controlled by a ramp wave (rising sawtooth).
This happened after reflashing the Bios. Does it have to do with the ME Region?

Thanks in advance.

[paulo66]

Re: X550CC no PWM for +VGFX_CORE

One more question: +NVVDD (NVidea Vdd?) is only 0.9V... is it the right voltage? Seems kind of low...

[paulo66]

Re: X550CC no PWM for +VGFX_CORE

Ah and the Caps Lock LED is always lit!

[Smoxx]

Re: X550CC no PWM for +VGFX_CORE

+NVVDD 0.9V is OK. Technically, the range is 0.6v~1.2v.

The absence of +VCCGT (VGFX_CORE) may be normal on boards with discrete graphics.

If all voltages are OK then can be really a BIOS issue or a bad EEPROM. You can try flashing a known good BIOS to a new IC to see if it makes a difference.

[paulo66]

Re: X550CC no PWM for +VGFX_CORE

Appreciated the prompt reply! There´s a number of different .bin files for this MB so I´m going to order a Pomona 5250 and a few 25Q64s and hopefully hit the right one. I´ll report back.

[paulo66]

Re: X550CC no PWM for +VGFX_CORE

EEPROMs arrived, 5250 clip not yet, but already flashed a new chip. And, soldered it the wrong way. Now it's OK, but there is a short across a few caps and a chip is getting hot. Can't install Boardviewer at work, so I can't see right now what chip it is. It's meant to convert the 19V to 3 and 5V though. So the shorted cap(s) must be at these outputs. I'll remove the caps one by one in the hope the chip is still fine.

[paulo66]

Re: X550CC no PWM for +VGFX_CORE

EC dead.

[Conste]

Re: X550CC no PWM for +VGFX_CORE

yep the EC is dead

[paulo66]

Re: X550CC no PWM for +VGFX_CORE

Yeah, after removing all suspect caps and the buck controller, the short was still across the +3VAO line. It was the EC +3VA inputs shorting the controller's outputs.
What is puzzling is why placing the BIOS the wrong way could cause such an issue. BTW the BIOS looks fine.

[mcplslg123]

Re: X550CC no PWM for +VGFX_CORE

Pin4 of bios chip is gnd-thats why the damage when u place it in wrong orientation.

[paulo66]

Re: X550CC no PWM for +VGFX_CORE

Sure, it's like with the DIL8 single supply opamps. Pin 4 is supposed to be grounded for it to work but it's not ground in itself, right? Even if pin 4 presented a too low resistance to the +3.3V line, it would be protected by the current limiting resistor. I mean, that series resistance would also present a safe load to the source of that voltage (EC I believe).