Folks! Following up on my previous thread here, we've got a new pile of dead graphics cards on the bench, and we're going to attempt to get at least one of them working.
For those who prefer video, I made a video version.
The cards in this case are Radeon R9 290X's - once again, we'll call them Card A, B and C.
Card C has belonged to me for several years. I actually traded for it with a fellow [H]er, back when it was relatively current. It works perfectly fine, although as you can probably guess from the photo, fans are somehow a consumable for these things.
Cards A and B I bought on ebay for about $20 apiece. They're both "dead," although Card B did actually produce a picture when I tested it a couple of weeks ago. Subsequent tests result in no picture, though. All three cards are identical physically, but Card A has the reference BIOS, as opposed to the Sapphire overclocked version that B and C have.
Given the apparently intermittent nature of the problem with Card B, we're going to concentrate on Card A as our candidate for repair first. Card C will serve as a reference, since it's undamaged, and works properly.
I've already removed Card A's heatsink. Unsurprisingly, there's no sign of physical damage to the front of the PCB.
But if we look at the back...
What's this? A missing cap? Hmm...
I'd be sort of surprised if the missing cap is the reason our card doesn't work. Those tiny caps are generally there to help filter out noise in the power plane, but as someone commented in the GTX 690 thread, his card didn't work with one of the smaller ceramic SMD caps broken off, so some designs may be sensitive enough where most of the caps are actually critical.
Before we just replace that capacitor, though, we should do some additional testing, to make sure it's related to our apparent problem. First, we'll check resistance on each of our voltage rails to see if any are shorted or open. Remember, we're looking for between 1 and 1000. Anything in that range is probably OK.
Here's VCore. Looks OK.
VDDCI (AKA memory power). Also looks OK.
The Aux rail. Also looks sane.
The 1.8 rail. I think this is related to the display ports... looks sane.
The .95 rail - I don't actually know what this does, but it's required for function. Also looks sane...
Unknown SOP-8 chip on the back of the card, pin 8, which is usually the phase pin on this type of regulator. This looks sane too, although I don't know for sure what this IC does.
Ok, that's all of our resistances. We didn't find any shorts, so that's good, and there's nothing with a huge resistance, which might indicate a totally open circuit. Now we need to power the card up and see which rails actually run.
VCore - this should be 1.0 - 1.2 volts. So we know this rail isn't working.
VDDCI - this should be about 1.5 volts, so we also know that this rail isn't working either. Notably, this and VCore share a pretty complex controller.
.95 - Ok, this one is working.
1.8v Rail - This one is working too.
Aux - Not working. I have a feeling that this may be waiting for an enable signal from something else, maybe the memory rail. I think I mentioned in the GTX 690 thread that the output of one VRM is frequently wired up to the enable input on another, so that rails start up in a specific order.
5V Rail - Also working. This is what powers the VRMs themselves. The controllers need power of their own, and in some cases it's also used for the gate drive of the MOSFETs.
Ok, so we've learned that something major isn't working at all. These symptoms lead me to suspect the problem lies in or around the control IC for our VCore VRM, which is shared with the VDDCI VRM. That's a pretty elaborate chip with 56 (!!!!) tiny pins. I think the next step is to look for anything simple, like power to it, or an enable signal that's missing, and for that, I need to consult the data sheet.
For those who prefer video, I made a video version.
The cards in this case are Radeon R9 290X's - once again, we'll call them Card A, B and C.
Card C has belonged to me for several years. I actually traded for it with a fellow [H]er, back when it was relatively current. It works perfectly fine, although as you can probably guess from the photo, fans are somehow a consumable for these things.
Cards A and B I bought on ebay for about $20 apiece. They're both "dead," although Card B did actually produce a picture when I tested it a couple of weeks ago. Subsequent tests result in no picture, though. All three cards are identical physically, but Card A has the reference BIOS, as opposed to the Sapphire overclocked version that B and C have.
Given the apparently intermittent nature of the problem with Card B, we're going to concentrate on Card A as our candidate for repair first. Card C will serve as a reference, since it's undamaged, and works properly.
I've already removed Card A's heatsink. Unsurprisingly, there's no sign of physical damage to the front of the PCB.
But if we look at the back...
What's this? A missing cap? Hmm...
I'd be sort of surprised if the missing cap is the reason our card doesn't work. Those tiny caps are generally there to help filter out noise in the power plane, but as someone commented in the GTX 690 thread, his card didn't work with one of the smaller ceramic SMD caps broken off, so some designs may be sensitive enough where most of the caps are actually critical.
Before we just replace that capacitor, though, we should do some additional testing, to make sure it's related to our apparent problem. First, we'll check resistance on each of our voltage rails to see if any are shorted or open. Remember, we're looking for between 1 and 1000. Anything in that range is probably OK.
Here's VCore. Looks OK.
VDDCI (AKA memory power). Also looks OK.
The Aux rail. Also looks sane.
The 1.8 rail. I think this is related to the display ports... looks sane.
The .95 rail - I don't actually know what this does, but it's required for function. Also looks sane...
Unknown SOP-8 chip on the back of the card, pin 8, which is usually the phase pin on this type of regulator. This looks sane too, although I don't know for sure what this IC does.
Ok, that's all of our resistances. We didn't find any shorts, so that's good, and there's nothing with a huge resistance, which might indicate a totally open circuit. Now we need to power the card up and see which rails actually run.
VCore - this should be 1.0 - 1.2 volts. So we know this rail isn't working.
VDDCI - this should be about 1.5 volts, so we also know that this rail isn't working either. Notably, this and VCore share a pretty complex controller.
.95 - Ok, this one is working.
1.8v Rail - This one is working too.
Aux - Not working. I have a feeling that this may be waiting for an enable signal from something else, maybe the memory rail. I think I mentioned in the GTX 690 thread that the output of one VRM is frequently wired up to the enable input on another, so that rails start up in a specific order.
5V Rail - Also working. This is what powers the VRMs themselves. The controllers need power of their own, and in some cases it's also used for the gate drive of the MOSFETs.
Ok, so we've learned that something major isn't working at all. These symptoms lead me to suspect the problem lies in or around the control IC for our VCore VRM, which is shared with the VDDCI VRM. That's a pretty elaborate chip with 56 (!!!!) tiny pins. I think the next step is to look for anything simple, like power to it, or an enable signal that's missing, and for that, I need to consult the data sheet.