It's been a while since we've collectively looked at a dead graphics card, but as I'm sure many of you can relate to, the last couple of months have been a real turd sandwich for me, and I just haven't felt like doing this, but that ends today.
I made a mistake uploading the video to Youtube, so I'll have to post that later, but it's coming, for those who prefer the sonorous melody of my voice...
On the bench, we have this handsome Sapphire Radeon R9 390 Nitro, which came to me in the same lot as the 980 Ti we looked at last time. I was kinda stoked to get this card in that lot, as I can't remember ever seeing a 300 series of any kind in person. I gather that almost everyone who might have wanted one already had a 200 series, and was unmoved by the minor improvements these brought to the table.
The seller described the card as totally dead, no fan spin or anything, which is a pretty clear indication of a power issue. Power issues are our favorite kind, as they're basically the only kind it's really practical to repair, particularly without a BGA machine, and furthermore, they're the sort of issue you're most likely to cause through overclocking, which is way more [H]ard than if your graphics card just lost it's will to live.
Our first step is to test resistance on the 12V input rails. We do this first so that if there's a short to ground on any of them, which is a common mode of failure, we know not to power the card up until we've cleared the short.
The near 8 pin connector. I mention in the video that this is probably OK, but hindsight being 20/20, I should have recognized this as faulty. Still, higher is better than lower here, so this is actually not the end of the world.
The far 8 pin connector. Looks healthy.
The PCI-E input pin. Also looks healthy.
Next, we'll plug the card in and apply power, so we can see which DC rails are actually running. We can't probe all of them with the backplate on there, but doing this with the heatsink installed is the best way to avoid the risk of smoking the GPU die. As described by the previous owner, we get nothing on the screen.
5V rail looks healthy.
3.3V also looks healthy
VCore, though, not so much. This should be in the 700 to 1200mV range. 230 is way low.
That's everything we can really test with the backplate in the way, so it's time to remove it.
With the card torn down, we have much better access to do our normal resistance tests. Here's VCore. Looks healthy. Normal should be something like 1.5-4 ohms.
The memory rail looks healthy. 90ish to 150 is what we expect here.
Memory controller also looks healthy. On a 290 or 290X, you'd expect a bit lower than this, but it's in the realm of normal.
The card's obviously dead, though, so something is clearly still wrong. Let's look at that near 12V input again. A nice thing about this card that I wish more graphics card makers would do is that they've included fuses on each of the input power rails. This means that we're much less likely to burn a hole in the board itself like the 980 Ti did if we have a short somewhere. In the case of that 980 Ti, I suspect the initial failure was actually a power stage, which shorted the input power to ground, and because there was nothing to turn it off, it melted the traces feeding that failed power stage together, destroying the board. A fuse on the 12V input power probably would have saved it.
We know from past experience that the 12V input on these GCN cards should typically be 5K-10K, so that near power connector that read in the millions is suspect. Let's check those fuses.
We've got continuity between the connector and the fuse...
But no continuity across the fuse. So, we know that this fuse is blown.
The other fuses appear to be OK. (Far 12V and PCI-E input, respectively)
It turns out that the near 8-pin is connected to the top 3 VCore phases, plus the memory power.
The far 8 pin is connected to the lower 3 phases.
If we check resistance to ground on the 12V input for those first three phases, we've got a dead short to ground, so now we need to figure out where it is...
Anyone care to guess as to how we find the short?
I made a mistake uploading the video to Youtube, so I'll have to post that later, but it's coming, for those who prefer the sonorous melody of my voice...
On the bench, we have this handsome Sapphire Radeon R9 390 Nitro, which came to me in the same lot as the 980 Ti we looked at last time. I was kinda stoked to get this card in that lot, as I can't remember ever seeing a 300 series of any kind in person. I gather that almost everyone who might have wanted one already had a 200 series, and was unmoved by the minor improvements these brought to the table.
The seller described the card as totally dead, no fan spin or anything, which is a pretty clear indication of a power issue. Power issues are our favorite kind, as they're basically the only kind it's really practical to repair, particularly without a BGA machine, and furthermore, they're the sort of issue you're most likely to cause through overclocking, which is way more [H]ard than if your graphics card just lost it's will to live.
Our first step is to test resistance on the 12V input rails. We do this first so that if there's a short to ground on any of them, which is a common mode of failure, we know not to power the card up until we've cleared the short.
The near 8 pin connector. I mention in the video that this is probably OK, but hindsight being 20/20, I should have recognized this as faulty. Still, higher is better than lower here, so this is actually not the end of the world.
The far 8 pin connector. Looks healthy.
The PCI-E input pin. Also looks healthy.
Next, we'll plug the card in and apply power, so we can see which DC rails are actually running. We can't probe all of them with the backplate on there, but doing this with the heatsink installed is the best way to avoid the risk of smoking the GPU die. As described by the previous owner, we get nothing on the screen.
5V rail looks healthy.
3.3V also looks healthy
VCore, though, not so much. This should be in the 700 to 1200mV range. 230 is way low.
That's everything we can really test with the backplate in the way, so it's time to remove it.
With the card torn down, we have much better access to do our normal resistance tests. Here's VCore. Looks healthy. Normal should be something like 1.5-4 ohms.
The memory rail looks healthy. 90ish to 150 is what we expect here.
Memory controller also looks healthy. On a 290 or 290X, you'd expect a bit lower than this, but it's in the realm of normal.
The card's obviously dead, though, so something is clearly still wrong. Let's look at that near 12V input again. A nice thing about this card that I wish more graphics card makers would do is that they've included fuses on each of the input power rails. This means that we're much less likely to burn a hole in the board itself like the 980 Ti did if we have a short somewhere. In the case of that 980 Ti, I suspect the initial failure was actually a power stage, which shorted the input power to ground, and because there was nothing to turn it off, it melted the traces feeding that failed power stage together, destroying the board. A fuse on the 12V input power probably would have saved it.
We know from past experience that the 12V input on these GCN cards should typically be 5K-10K, so that near power connector that read in the millions is suspect. Let's check those fuses.
We've got continuity between the connector and the fuse...
But no continuity across the fuse. So, we know that this fuse is blown.
The other fuses appear to be OK. (Far 12V and PCI-E input, respectively)
It turns out that the near 8-pin is connected to the top 3 VCore phases, plus the memory power.
The far 8 pin is connected to the lower 3 phases.
If we check resistance to ground on the 12V input for those first three phases, we've got a dead short to ground, so now we need to figure out where it is...
Anyone care to guess as to how we find the short?