Re: Mining LiteCoin and PrimeCoin and PC just shutting down - seeking advice
Ohh, good to hear it's winter there! From a mining perspective, that is... 
Since your cards are not overclocked and assuming the manufacturer set them to run at a sane voltage, I'd think that you would have been ok (but pushing the limits) on a 750W PSU. Nonetheless, it seems that your particular unit may not be quite up to the task.
My best guess would be that the extra load from primecoin mining was finally enough to push things over the edge (as I understand it, that was the first time you'd run into shutdown issues?). The PSU somehow managed to support the load of primecoin + litecoin mining for a week, but I suppose that was enough to do it in. Continuously supporting a load that meets or exceeds a PSU's limits for extended periods of time will cause it to wear out exponentially faster than normal (if it doesn't outright kill it). PSU manufacturers often take for granted that most people buying their units (especially the cheaper ones) will use less than half the unit's rated capacity. For this reason they'll often build the units just good enough to say that they're rated at XXX watts, but the unit is not truly capable of delivering that kind of power continuously. Of course, on the other hand, sometimes high quality PSUs are capable of performing beyond their rated capacity, but I wouldn't recommend that! In your case I think the issue is partially the high load that CPU+GPU mining placed on the PSU and partially that the PSU itself may not be the greatest to begin with.
A random thought; another thing that may be compounding the issue is that the overcurrent protection circuit in the PSU can wear out too. Particularly if it gets tripped a lot, it can become weaker and more sensitive causing it to trigger sooner and sooner. I honestly don't know if this is playing a part at all or not -- there are really all sorts of things that could be going wrong to cause the odd issues that you're having.
At three months old, your PSU is still fairly new so maybe you can try exchanging it with the manufacturer. I'd expected you to say it was 5 years old or so.
Nonetheless, if you still plan to CPU and GPU mine simultaneously, I'd recommend that you upgrade. If you do go this route, definitely find something that's at least 80+ silver rated -- the difference in efficiency will more than make up for the initial added cost within six months of mining.
Anyways, I suppose we still can't be 100% sure that the PSU is the cause yet. I definitely like to be sure before buying new parts. To clarify: when you tested with the 650W PSU, it only shutdown when you tried to run primecoin AND litecoin mining simultaneously, right? I'd guess you were probably just drawing too much from the 650W which caused it to shutdown too. If you have a friendly local computer shop you may be able to get them to bench test your system with a different PSU (say, a strong 850W+ to rule out drawing too much current) for little or no cost. If the problem still persisted then, you'd at least know for sure that the issue is not your power supply. If it wasn't the power supply my next thought would be maybe the motherboard. I would say with near certainty that the issue is not the CPU or memory and probably not the GPUs.
Good luck in getting things worked out!
Since your cards are not overclocked and assuming the manufacturer set them to run at a sane voltage, I'd think that you would have been ok (but pushing the limits) on a 750W PSU. Nonetheless, it seems that your particular unit may not be quite up to the task.
Question, it ran fine for just over two months (on GPU mining) before the problem started - is there a possible explanation for that? Possibly wearing down already?
My best guess would be that the extra load from primecoin mining was finally enough to push things over the edge (as I understand it, that was the first time you'd run into shutdown issues?). The PSU somehow managed to support the load of primecoin + litecoin mining for a week, but I suppose that was enough to do it in. Continuously supporting a load that meets or exceeds a PSU's limits for extended periods of time will cause it to wear out exponentially faster than normal (if it doesn't outright kill it). PSU manufacturers often take for granted that most people buying their units (especially the cheaper ones) will use less than half the unit's rated capacity. For this reason they'll often build the units just good enough to say that they're rated at XXX watts, but the unit is not truly capable of delivering that kind of power continuously. Of course, on the other hand, sometimes high quality PSUs are capable of performing beyond their rated capacity, but I wouldn't recommend that! In your case I think the issue is partially the high load that CPU+GPU mining placed on the PSU and partially that the PSU itself may not be the greatest to begin with.
A random thought; another thing that may be compounding the issue is that the overcurrent protection circuit in the PSU can wear out too. Particularly if it gets tripped a lot, it can become weaker and more sensitive causing it to trigger sooner and sooner. I honestly don't know if this is playing a part at all or not -- there are really all sorts of things that could be going wrong to cause the odd issues that you're having.
At three months old, your PSU is still fairly new so maybe you can try exchanging it with the manufacturer. I'd expected you to say it was 5 years old or so.
Nonetheless, if you still plan to CPU and GPU mine simultaneously, I'd recommend that you upgrade. If you do go this route, definitely find something that's at least 80+ silver rated -- the difference in efficiency will more than make up for the initial added cost within six months of mining.Anyways, I suppose we still can't be 100% sure that the PSU is the cause yet. I definitely like to be sure before buying new parts. To clarify: when you tested with the 650W PSU, it only shutdown when you tried to run primecoin AND litecoin mining simultaneously, right? I'd guess you were probably just drawing too much from the 650W which caused it to shutdown too. If you have a friendly local computer shop you may be able to get them to bench test your system with a different PSU (say, a strong 850W+ to rule out drawing too much current) for little or no cost. If the problem still persisted then, you'd at least know for sure that the issue is not your power supply. If it wasn't the power supply my next thought would be maybe the motherboard. I would say with near certainty that the issue is not the CPU or memory and probably not the GPUs.
Good luck in getting things worked out!