MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

[whc14765]

I got an old broken GTX 970 on eBay for cheap, just to see if I can repair it. I haven't repaired anything before but I do have electronics experience.

No physical damage at all.
Does not power on at all.

The only issue I see is that the +12V from the 6pin PCIE power connector is showing 5.5ohms to GND. I have been tracing with the schematics and I can't seem to find where the 5.5 ohm short is.

Still waiting on my freeze spray before I can find it thermally. Any advice on how to locate the 5.5 ohm short until then?

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

One of the mosfet might have blown closed and you are looking at the ohms of the Vcore. Check if they are the same.

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

Measure those inductors if it's 5.5 ohms because that's suspiciously close to what vcore ohms are on those cards.

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

If it is the same I hope the Psu turned off quick enough and saved the GPU core from direct 12volts otherwise you got a dead card. However 5.5 ohms on vcore might mean your card is still alive or half dead.

[whc14765]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

I think I found where the 5.5ohms are coming from. One of the VCORE MOSFET packages is showing the 5.5ohms across it's terminals (U4541)



I actually see one solder joint extruding a bit, almost like someone tried to reflow/replace this.

[whc14765]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

Is it possible to test a card with one missing phase of the VCORE buck converter? I mean if I remove U4541 and the 5.5ohm short is gone, would the card boot up?

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

That mosfet must be the one connected to the 6 pin 12v which makes sense. Unsolder that mosfet and check for short.

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

If there isn't any shorts elsewhere on the board and the short on 12v 6 pin is gone if it was me I'd do a quick test.

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

The card might have other problems so you should check resistances on the card.

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

When a mosfet fails it overheats like crazy and creates extruded solder balls like that so this looks promising.

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

Also you need a hot air rework station to remove those mosfets and find out why that mosfet blew. It might be the mosfet driver of that chip or even the voltage controller itself.

[whc14765]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

Yeah, I have a hot air rework station.

About the other resistances - is there a list somewhere on what I should check and what the resistances should be? The 8pin PCIE connector is fine - no shorts. The 6pin was showing this 5.5ohms between +!2V and GND.

This is my graphics card repair so I'm not too familiar what resistances I should be getting.

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

Your gonna have to find a boardview or schematics. For the 5V, 12v, pex, 1.8v rail and memory resistances just search them up on google or youtube repair videos of similar cards.

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

You also have to remove the choke that is connected to that mosfet otherwise you'd have to remove all the mosfet connected to the 12v 6pin

[whc14765]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

UPDATE: I removed the MOSFET package U4541, unforunately, now I see 3ohms from +!2V to GND on the 6pin PCIE connector Looks like there's another short somewhere else.

OOPS: nevermind, just realsied I removed the wrong FET . No more short anymore !

[whc14765]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

You also have to remove the choke that is connected to that mosfet otherwise you'd have to remove all the mosfet connected to the 12v 6pin

How the heck do you remove that thing - just won't come off. I added tons of normal solder but it dissipates heat too quickly. My iron and air station are at 480C.

[princeatom]

Re: MSI GTX 970 4G V316 1.3 - 5 ohms from 12V to GND

Grats so far, and yes that sucker is hard to remove. Gotta get someone to help you hold the heat gun on it and use the soldering iron at the same time. Otherwise it's going to take about a minute 30s or more to remove it with the rework station at 450-500c temp. If your not planning to use the choke later on.