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Earlier this year we have published a tutorial on how to raise the Power Target limit on GTX 750 – the first Maxwell-based video card. Now it is time to provide an update on how you can raise the maximum power limit of the new Maxwell GPUs – GTX 970 and GTX 980. The thing you need to do and the tools required are pretty much the same, however you need to use more up to date version of nvflash that supports the new cards. Also as compared to GTX 750 where many of the cards do not have additional PCI-E power connectors with GTX 970 and GTX 980 you also need to raise the limits of the PCI-E lines as well in order to allow the card to take advantage of the full increase in TDP you can set. And if you wonder why you would need to raise the power target limit for standard pretty low TDP values set for most GeForce GTX 970 and GTX 980 cards – it is quite simple – more overclock resulting in more performance and higher hashrate. The standard TDP levels set in the video BIOS of the new Maxwell cards are pretty much fine for the default operating frequencies and the default boost frequency, but are not enough to realize the full overclock potential of GTX 970 and GTX 980. With a little increase in the TDP limits and proper cooling many of the GeForce GTX 970 and GTX 980 based video cards are able to hit and keep a boost frequency for the GPU at about 1500 MHz or even more.
Back with GTX 750 we used a tool called Kepler BIOS Tweaker and you can still use it for basic TDP limit modifications for the new cards, but now there is a new version of that tool with official Maxwell support. It is now called Maxwell II BIOS Tweaker and the latest version for the moment is 1.36. If you are already familiar with the Kepler BIOS Tweaker tool, then you should not have any problems using the new tool. You also need to use a new version of the nvflash tool for saving the original and flashing the modified video BIOS on the video card, we have included the required files in the package below. Alternatively you can also use the latest version 0.8.0 of the tool GPU-Z to save the video BIOS as previous versions had issues when trying to save the BIOS file of GTX 970 and GTX 980 video cards, unlike the version of nvlfash that we’ve had to use for DOS for the GTX 750 modification. Now you can use a modified windows version of nvflash for easier saving and flashing of the video BIOS without worrying about getting a certificate error, the only thing you need to do before saving or flashing the video BIOS from windows is to first disable the video card driver from Device Manger.
How to backup your current BIOS with nvflash:
nvflash -b backupbios.rom
How to flash the modified BIOS with nvflash:
nvflash -6 modifiedbios.rom
The easiest way to figure ut what values you need to modify to increase the TDP limit of your particular GPU is to use a tool such as MSI Afterburner or EVGA Precision X for example that gives you a slider to increase the Power Target limit. You need to note what is the maximum value in percent available for your BIOS and then look for the field with that Max value in the Power Table panel of the Maxwell II BIOS Tweaker tool. This will show you the total card TDP value, the one you need to increase, but not the only value you will most likely have to increase. In our case the 100% (standard) TDP limit of a GTX 980 GPU is set at 180W with a maximum user selectable value of 225W, however there is a bit of a catch here. The top three fields above the total TDP value are respectively for the PCI-E slot power (66W by default) and the first and second PCI-E power connectors on the card (75W each). You cannot modify just the total TDP value and not also increase the separate power lines maximum as if you do not the BIOS will still limit the power that the video card uses to the combined maximum of the PCI-E slot and the two additional PCI-E power connectors. So if we want to increase the total maximum TDP of the video card to 275W (+153%) as the maximum user selectable as in the example above, then we would also need to increase the first and the second PCI-E standard power limits by adding 25W more to each and this way we would be able to get to the desired maximum set for the card total TDP. We are not modifying the 100% value of the total TDP to 275W, but instead leave the default 180W TDP value there, so that we can increase the maximum (Max value) with Afterburner or Precision X if we need to, but if we don’t the card will still have the standard 180W TDP limit.
Do note that in order for the increase of the maximum TDP level to have some effect on performance you would also need to overclock the video card by increasing the GPU and video memory frequencies. As we have mentioned with a good cooling (even the stock one can do just fine with increased fan speeds) you should be able to reach a maximum boost frequency of 1500 MHz or even higher with most GTX 970 and GTX 980 cards. In fact you might be able to hit such high OC frequency even without increasing the TDP level, however if you start hitting the standard TDP level of the video card the boost frequency will drop down. In order to be able to high the maximum stable boost frequency of the video card and keep the card working at it you will have to increase the TDP level, so that the GPU will have enough headroom. Do note that not all crypto mining algorithms will utilize the maximum available TDP level, so for some of them increasing the TDP level may not be required at all.
Nvidia is advertising their new GeForce GTX 750 Ti GPUs based on the new more power efficient Maxwell architecture as being with 60W TDP, but in truth they seem to be much more power efficient than that. A lot of people are already interested in using these new GPUs from NVidia for mining, because the performance that the Maxwell delivers seems to be very good in terms of hashrate per Watt ratio. When you use CUDAminer to mine with the GTX 750 Ti you will notice the card will quickly reach the 100% power target limit and normally you are not allowed to increase the power limiter of the card above the 100% value, you are allowed to only lower it further. The interesting thing here however is that the default TDP limit for GTX 750 Ti is actually set to 38.5W inside the BIOS and the minimum of 78% you can go down to is equal to just 30W TDP and as we’ve mentioned Nvidia is talking about 60W TDP for these cards. The fact that the cards are actually limited to 38.5W by their power limiter is something that can prevent you from squeezing the maximum performance that you can get by overclocking the GPU and/or the video memory of the card, so increasing the TDP limit by modifying the BIOS and reflashing the video card with the modified BIOS can help you with that.
Since many of the GeForce GTX 750 Ti video cards do not have external PCI-E power connector you will be limited to the maximum power that these cards will be able to use due to the 75W maximum of power that PCI-E x16 slot can provide by specifications (66W for the 12V line that you will be actually using, the other ~10W are for the 3.3V line). But even this will provide more than enough headroom since the default TDP limit is not 60W as we though, but really just 38.5W, so lots of headroom for overclocking. In order to be able to modify the BIOS of your video card you will need to first save the original one from the card, you can use GPU-Z for that and make sure you keep the original BIOS as a backup and save the modified one as a separate file (you can also backup the BIOS with the nvflash under DOS if you are having trouble with GPU-Z). Then you need to fire up Kepler Bios Tweaker and open up your BIOS file and edit is as shown in the screenshot above (left is original, right is the modified) in order to get 65.5W as the maximum TDP of the card. After that you need to flash the BIOS back to your card using the provided nvflash, you can download the flasher and the Kepler Bios Tweaker along with a standard BIOS from a reference 750 Ti and a modified version of that BIOS to allow 65.5W TDP from the link below. We suggest that you save the BIOS from your own video card and modify it, also do have in mind that modifying and flashing modified video BIOS to your video card can be dangerous, so you should be extra careful what you are doing and not modifying things that you should not or does not know what they are for!
The procedure described above will work for increasing the power target limit on other video cards as well not only on GTX 750 Ti, however before increasing the limit make sure that your video card cooling can keep the card cool enough. Using the video card fro mining will bring the power target to 100% in most cases even without overclocking the card additionally, so just by increasing it you might e able to squeeze some extra performance even without overclocking it further. The version of nvflash provided in the archive below is the latest one that will work with the GTX 750 Ti as well as with older video cards, it is the DOS version of the flasher as the Windows version of nvlfash does not seem to work properly – it does not want to flash the modified BIOS to the card saying that the BIOS digital signature is wrong. No problems flashing the modified video BIOS though trough the DOS version of nvflash 5.163, so we have only included the DOS version that will work with the method described above. There are two BAT files configured to flash the modified video BIOS and to restore the original version of the included reference design board BIOSes, you just need to run “nvflash your_bios.rom” and confirm with “y” when asked by nvflash (make sure you’ve made a backup of your original video BIOS first!). Again, be aware that video BIOS flashing and modification can be dangerous and can temporary render your video card useless, at least until you reflash it with the original BIOS, so do keep a backup of the original! Also note that increasing the TDP limit beyond the recommended value above could also be dangerous, so be well aware that this modification can be dangerous! Feel free to share your results for overclocking and mining hashrate after increasing the TDP limit of your GTX 750 Ti or another board in the comments below.