Re: Sapphire HD 7870 possible short
I think you have the VRM sections mixed up. The GPU takes a lot more power than the RAM, so it will have more power phases.
A short between Drain and GND on the lower FET could be a shorted FET (quite likely) BUT - it could also be anything in parallel with one of those FETs, like an output filter capacitor (I'd be wary of those SMD output capacitors), some IC, or even the GPU itself (that is unlikely though).
Isolating the FETs for testing by removing the coils should work, but you will need a good hot air station to do that as they will suck up a lot of heat... might pay to inject current instead.
If you want to try injecting current, you don't need a huge amount. Just enough to heat the bad part a little. You can put isopropyl alcohol on them all and see on which one(s) it evaporates the fastest. Get a current limited supply set to something less than the full rail voltage, and limit it to 100-200mA or something to start with. You can turn up the current a bit if you need to but if you just whack something capable of several amps straight on there, you may burn up the faulty part so bad it cooks the board and then you'll be screwed.
If you have a very sensitive meter, you can also measure mV drop across each FET\Capacitor and see where the drop is lowest - that should be your shorted part. Or do the same thing with Ohms and power off. That will require a very good meter though.
In any case - do not exceed whatever voltage would be on the rail during normal operation, otherwise you risk blowing the GPU\RAM or whatever else is powered from that rail.
Also, in the interests of avoiding ESD damage, it may pay to keep the card off carpet....
And please upload your photos to the forum instead of elsewhere.
I think you have the VRM sections mixed up. The GPU takes a lot more power than the RAM, so it will have more power phases.
A short between Drain and GND on the lower FET could be a shorted FET (quite likely) BUT - it could also be anything in parallel with one of those FETs, like an output filter capacitor (I'd be wary of those SMD output capacitors), some IC, or even the GPU itself (that is unlikely though).
Isolating the FETs for testing by removing the coils should work, but you will need a good hot air station to do that as they will suck up a lot of heat... might pay to inject current instead.
If you want to try injecting current, you don't need a huge amount. Just enough to heat the bad part a little. You can put isopropyl alcohol on them all and see on which one(s) it evaporates the fastest. Get a current limited supply set to something less than the full rail voltage, and limit it to 100-200mA or something to start with. You can turn up the current a bit if you need to but if you just whack something capable of several amps straight on there, you may burn up the faulty part so bad it cooks the board and then you'll be screwed.
If you have a very sensitive meter, you can also measure mV drop across each FET\Capacitor and see where the drop is lowest - that should be your shorted part. Or do the same thing with Ohms and power off. That will require a very good meter though.
In any case - do not exceed whatever voltage would be on the rail during normal operation, otherwise you risk blowing the GPU\RAM or whatever else is powered from that rail.
Also, in the interests of avoiding ESD damage, it may pay to keep the card off carpet....
And please upload your photos to the forum instead of elsewhere.
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