Vega 64 - missing PX_EN

[gurj1979]

Hi guys,

So for the fan to turn on and give 5v at the pin, it needs PX_EN to turn the controller on. The GPU generates this signal and sadly it is showing as 0v.

The card shows display fine and runs as normal, but the fan isn't kicking in due to missing PX_EN signal.

Any pointers and fixes ?

[Prott]

Re: Vega 64 - missing PX_EN

Hi,
if I understand it correctly - if the card runs fine it definitely should have a PX_EN signal from the GPU. Without it it wouldn't run at all cause this signal does bunch of other important stuff.

Try finding out where it gets lost. If you are measuring it on the leg of an IC, for example, try to check if the leg has a good connection with the pad.

[ktmmotocross]

Re: Vega 64 - missing PX_EN

what about resistance to gnd on that pin?

[gurj1979]

Re: Vega 64 - missing PX_EN

Yep. Resistance is 1.2 Mohm on both sides of resistor at the GPU side. So resistor has a value of zero ohms (not checked the actual value in schematics because I had to shoot off to work).

[gurj1979]

Re: Vega 64 - missing PX_EN

I've just measured the value of R109. It is 1K, same as schematics show.
What next? Possibly dead PX_EN or reball ?

[Prott]

Re: Vega 64 - missing PX_EN

If there would be no PX_EN from the core the card wouldn't work at all.

[gurj1979]

Re: Vega 64 - missing PX_EN

I've had the card enter Windows with drivers. But PX_EN is not turning on and fan ain't spinning because of this.

[Prott]

Re: Vega 64 - missing PX_EN

Ok, I went through the schematic and correct me if I am wrong, but it looks like PX_EN actually has to be low during normal operation. If it's high it pulls down the REG_GRP_A_PWRGD which in turn disables the buck converter for the +VPP.

That would solve the issue of the card working even though PX_EN is low.

[gurj1979]

Re: Vega 64 - missing PX_EN

Thanks Prott. But how does that explain the fan never kicking in, and the GPU overheats and forces machine to shut down. The heatsink become mega hot.

[Prott]

Re: Vega 64 - missing PX_EN

I am checking the circuit.

So, the problem is that the fan never gets 12v? Can you measure the pins on the fan header?

Also, did you check the 0 ohm resistors for the fan? And lastly... is the fan motor working? :-)

I don't think PX_EN is the issue.

[gurj1979]

Re: Vega 64 - missing PX_EN

I've uploaded 2 pics. One of them showing display output. PX_EN still missing but I have 3v at Q1032 pin 3. Can't make sense of this one.

[gurj1979]

Re: Vega 64 - missing PX_EN

I've tried 2 fans. Original and eBay because I had doubt at the start.
Pin 1 = GND
Pin 2 = 0.035v
Pin 3 = 3.9v
Pin 4 = 0.082v

Forgot to mention LED light is RED at D4002

[Prott]

Re: Vega 64 - missing PX_EN

I've uploaded 2 pics. One of them showing display output. PX_EN still missing but I have 3v at Q1032 pin 3. Can't make sense of this one.

That seems like normal behaviour. PX_EN, when high, pulls REG_GRP_A_PWRGD low through Q1032.
REG_GRP_A_PWRGD itself is powered by 5V through a voltage divider and a 0 ohm resistor.

[Prott]

Re: Vega 64 - missing PX_EN

I would check R240 (should be 20k) and R213 (should be 0 ohm). Also try checking resistance between the second pin of the fan header (should be 12V ? ) and ground. Also the same pin and 12 V. On my working VEGA both of those are in the range of 10+ kOhm and rising.

[gurj1979]

Re: Vega 64 - missing PX_EN

R240 = 20k.
R213 = no component there 4.5K.
Fan connector voltages listed in above reply.

[gurj1979]

Re: Vega 64 - missing PX_EN

I just noticed U500 had some dodgy soldering from pin 1 to pin 14. Reflowed it, now it wont turn on. 12v & 3v still around the board, but none of the MOSFETs will turn on.
Either I've just killed U500, or it's not getting correct data from the components connected pins 1-14.

[Prott]

Re: Vega 64 - missing PX_EN

Hard to say - I only have a schematic for Strix, which is slightly different. Though I am surprised there's no 12 V for the fan as that pin should be pretty much connected straight through to the 12 V bus.

1. The resistor on R213 was never there or is it physically knocked off / blown off?

2. Next thing to check is the Q211 mosfet. It should have 12 V on the second leg and positive voltage on the first leg.

3. If there's 12 volts but no voltage on the base (1st leg) try checking Q212. Is there any voltage on the leg no. 5?

[Prott]

Re: Vega 64 - missing PX_EN

I just noticed U500 had some dodgy soldering from pin 1 to pin 14. Reflowed it, now it wont turn on. 12v & 3v still around the board, but none of the MOSFETs will turn on.
Either I've just killed U500, or it's not getting correct data from the components connected pins 1-14.

Check for shorts, mainly on 5V. Short on 5V would not show up outside of the card.

[gurj1979]

Re: Vega 64 - missing PX_EN

Check for shorts, mainly on 5V. Short on 5V would not show up outside of the card.

Thanks for the tip. I'll check another time, busy with other jobs now

[Prott]

Re: Vega 64 - missing PX_EN

To make it easier - check the back voltage regulator (under the U500). It's upmost right leg (closest to the HDMI ports) should have a resistance to ground in the range of kOhms.

By the way, I confirmed that on my working Vega the PX_EN is indeed low while the card is in operation.

EDIT: Could you please help me and point me to the direction of the 1k R109 resistor? I need to troubleshoot another Vega card.