Repair r9 390 nitro gpu

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I removed the coil with the help of both the iron and the hot air and now I can see that the caps are still shorted to ground and the aux vrm does give 0.22v and the 5v regulator works fine as there is 12vvan5v at the sides.

[Shock]

So showing low resistance 0.1 ohms? which caps?

[JKKDev]

At this point, I would remove the IR3553. If that's not causing the short then one of the caps is shorting. Nothing else is there as far as I can see.

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So showing low resistance 0.1 ohms? which caps?

Yes 0.1ohm on the filtering caps of the aux vrm

[JKKDev]

So showing low resistance 0.1 ohms? which caps?

Yes 0.1ohm on the filtering caps of the aux vrm

Can you show exactly where you measured the 0.1 ohm?

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At this point, I would remove the IR3553. If that's not causing the short then one of the caps is shorting. Nothing else is there as far as I can see.

If the gpu itself was shorted, it would heat up right?

I don't think that the mosfet is shorted as there us no short between drain and source but is a resistance of 5.8 kohm.

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Those 2 electrolitic chaps and 4 ceramic ones.

[JKKDev]

Those 2 electrolitic chaps and 4 ceramic ones.

And you are sure that your ohms measurements are valid? If that's the case something has to be shorted as a voltage rail shouldn't have a 0.1 Ohms resistance to ground. Something also had to get fried at some point (I think it's the IR3553) if nothing is heating up but the voltage rail isn't present. You never confirmed if the IR3553 has the 12V present.

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The 12v is present at the IR3553 and befor removing it, the voltage at the coil was 0.22v but now that I have removed it, the voltage us 0.03v. At this point I think that the problem is with the control ic s.

Also let me know what you guys think about the rx470 gpu that I posted earlier.

[JKKDev]

I don't see how it would be a problem with the control as you still have a short... I would still remove the IR 3553 and the caps until the short clears. Basically, you have isolated a very small area of the board between the IR3553 and the coil which only has capacitors on it. As there is a short here it's either caused by the IR3553 or the caps.

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I don't see how it would be a problem with the control as you still have a short... I would still remove the IR 3553 and the caps until the short clears. Basically, you have isolated a very small area of the board between the IR3553 and the coil which only has capacitors on it. As there is a short here it's either caused by the IR3553 or the caps.

I have desoldered the IR3553 and the shirt is still there.

[JKKDev]

I don't see how it would be a problem with the control as you still have a short... I would still remove the IR 3553 and the caps until the short clears. Basically, you have isolated a very small area of the board between the IR3553 and the coil which only has capacitors on it. As there is a short here it's either caused by the IR3553 or the caps.

I have desoldered the IR3553 and the shirt is still there.

Now do the circular caps.

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Done that and the shirt is still there

[JKKDev]

I know this seems dumb but I'm 100% sure there is something wrong here. I would try removing all the small caps that are connected to this one pad one by one and if the short isn't gone just resolder it back. Go around on both sides and something has to give at this point.

If you feel like it, you could try visually figuring out if this rail goes anywhere else on the board but I'm almost certain that it shouldn't leave before going through the coil.

EDIT: Hold up, is the R646 connected to this pad? If so measure it and if it shows a short try removing it.

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 I did remove anithing that I was thinking it might been shorted but there is nothing that have been changed.

I resoldered the IR3553 but now instead of the 0.22v I get 0.10v

At this moment I think that I will wait until I get the other gpu and see I the simphtoms are similar.

Also, do you think that I have any chance to repair the rx470? I posted some pictures earlyer and I was wandering if this one is easyer to repair?

[JKKDev]

I'll be honest... Lines across the screen can't be a good sign... But I don't know enough about it to help you out. You could try different types of outputs (if there are any - hdmi, dvi, vga). If they all exhibit the same behavior there is something wrong with the core imo.

You definitely can't probe it like you can the r9. The only thing you could look at are the voltage rails. If those are nominal then something's up with the core. If some are outside spec or have high ripple then it's the supply rails. But without a scope, this will be hard to figure out.

One thing before we give up on the R9 just to make sure. Which pad of where the coil used to be is shorting to ground?

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I will attach a photo with the pads.

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Here

[JKKDev]

Without knowing where the rail goes there's no way you're going to track this short down... You can check the capacitors behind the core. If any of them have ground on both sides you're most likely done. Anyway, I'm not sure I can help you any further. If you have any ideas of your own feel free to share

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All the caps on the core give a reading of 0.2ohm so the core might be OK, I hope.

I really appreciate the help and the interes in my situation. You guys are awesome!

If anyone have any idea on what the problem might be, please let me know.

[Shock]

Please don't start posting multiple cards faults in the same thread! It's extremely confusing and annoying reading, start a new thread for a new repair.

According to this video below that Aux VRM section eventually goes to the GPU memory controller. There may be additional components on the GPU side or rear it feeds.

To do that low power short finding troubleshooting technique you mentioned you need to inject a low voltage on that rail and use an adjustable current limiting power supply. Or some people use a battery or simple DC voltage source and use a current limiting resistor. The idea is the low voltage and limited current means the short can only dissipate the maximum power you have predetermined and heat up rather than fuse.

Rasz and Wraper forum members here seemed to have worked on a lot of GPUs so I have messaged them for their comments.

[Shock]

Just to confirm that you are looking at an actual issue. Was there no voltage on that AUX VRM output to ground and then you removed the inductor and then the VRM was suddenly showing voltage to ground again? If so that looks like a short on that VRMs output, it can mean the VRM is faulty only under load or/and a component or trace short somewhere on the output of that VRM.

[wraper]

If upper MOSFET was short, some or all RAM chips should be dead because of overvoltage. GPU memory controller might be bust as well, but they are more robust than RAM IME. I personally would attach power to RAM from external PSU and watch with IR camera. Evaporating alcohol trick will not work because heat dissipation on dead chips will be minimal due to very low resistance. They barely heat up a few degrees maximum even if you push 5A into the power rail.

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This is what I was thinking as well that the memory chips might have gone bad as the ram vrm was shorted but after taking the mosfet out, I was able to see that they are fine and only the pads are shorted. Thus if I try to take out the inductor from that rail, it will tell me if the short is on the ram chips or at the driver part, right?

Also, I don't have a psu with curent limiting but I have some step up and step down convertor one of which actually has a curent limiting setup. Can I use that one whit a pc psu and insert 2v at 3A?

And yes, after removing the inductor on the aux vrm, from ground there was a voltage of 0.22~0.10. Also I removed one inductor fro the core vrm and as well the voltage raised from 0v to 0.22v

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I removed the inductor from the memory vrm and the short between drain and source is gone but there is 0.2 ohm from ground to the other side of the inductor