With the recent acquisition of an AMD HD 7990 GPU for Litecoin mining, I had some concerns. In my first post on the subject, I discussed the excessive heat issues that I encountered when mining at full power.
I’ve implemented solutions to problem and documented fully here. Now, I’ve taken the time to disassemble the 7990 and apply new thermal compound. This resulted in a 3C-5C temperature reduction, and below I’ll be discussing the process and full outcome.
VTX3D HD 7990 and Heat
The card manufacturer for my 7990 is VTX. It’s built on the standard AMD spec, and comes with off-the-shelf cooling. I noticed right away that heat would be an issue as soon as I began testing cgminer. Heat climbed to over 100C if I let it run any longer than 15 minutes, AMD recommends keeping the card at or below 85C.
While I have tweaked my config, found a stable voltage setting, and effectively reduced temps while still maintaining the high hash rate expected of a 7990, I figured that I could reduce heat by another few degrees if I changed out the stock TIM.
Thermal Compound Selection
Thermal compound can be a peculiar medium. While many insist that it doesn’t matter if you use the ceramic-based, silver-based, or diamond-based, I have always had good results when applying an a aftermarket TIM. Results are only usually 2C-5C difference, but when it comes to 24/7 mining at full load any reduction can help prolong the life of your GPU.
I chose to use Arctic Silver’s Ceramique 2 for a couple of reasons. At first I was on the hunt for some Arctic Silver 5 but my local Radio Shack didn’t keep any in stock. I have always have had good results with AS5 and so wanted to stay with their product line. When I couldn’t find AS5 at any other PC stores I went with the next best product in the Arctic Silver line, Ceramique 2. While I think AS5 might have provided another ~1C reduction, the Ceramique definitely showed better performance over the stock compound.
Taking apart the card is pretty straight forward. There’s a step-by-step video here.
- The first step to disassembling the HD 7990 is to remove the back plate screws. Once the 8 screws are removed the back plate comes right off.
- There are 4 screws along each side of the card. Remove these from both sides:
- The previous step allows for the fan mount to be removed. However, removing it can be a little bit tricky. There are two connectors that attach right underneath the heatsink fins. Once you’ve pulled the faceplate and fans away from the card a bit, you will see the connectors on opposite corners. Be sure to disconnect these before trying to fully remove the fans:
- Once the fans have been removed, turn the card over to unscrew the heatsink mounts. Be sure to keep track of all the screws and the direction that the brackets lie.
- Now that the brackets have been removed the heatsink should be loose. It is a bit difficult to try and pull the sink away from the card by hand, so I used a flathead screwdriver to very gently pry the heatsink from the board.
Once the heatsink is removed you can investigate the status of the current TIM application. In my case, I felt that the manufacturer coverage was a little spotty. Not only does it look like there was way too much thermal compound, but it also contained a lot of air bubbles.
You can see where the corners of the GPU are bare, and also the large amount of air bubbles present throughout. This could have been a factor in my particular heat issues and may well be the case on other cards from VTX.
I used 90% rubbing alcohol with q-tips and coffee filters to remove the compound. For one heatsink, it was very easy to get all of the goo off. The other was a different story.
This heatsink had a bunch of residue that just would not come off. Only after 45 minutes of scrubbing vigorously with rubbing alcohol soaked coffee filters (also tried acetone) did this ever become acceptably clean. Here is the final product after cleaning the heatsinks and the GPUs:
Applying New TIM
I selected Ceramique 2 from Arctic Silver’s product line. It is a non-capacitative substance, unlike AS5, and so reduces risk of any shorting on the board from accidental contact on an exposed trace or other component.
Regarding which technique to use for applying the thermal paste, I’ve done some research and found that there are only slight differences in coverage with the different methods. What’s more important is the amount that is being used. Thermal compound is most effective when only a very thin layer is present between the GPU and heatsink surfaces. It’s only meant to interface between the two and not actually absorb or dissipate the heat, that’s the job of the heatsink. Here is a good article on Thermal Paste Application Techniques that I found very useful. It seems that probably the best method is using the X shape, but this is somewhat preferential.
I used the spread technique to apply the new thermal paste. I made sure there was only a thin layer by starting with a small pea-sized amount.
Once the new compound is applied, reconnecting the heatsink is the next step. This can be kind of tricky because there are two heatsinks and they are not connected together. I put one on at a time and secured it with the bracket before moving on to the next. When placing the heatsink on the GPU it’s super important that the contact is made flush. That way the compound will spread evenly and more of the chip’s surface has a chance to be covered. Once the one heatsink is attached and secured, move on to the next.
After the heatsinks are secured, just reverse the process above in reassembling the pieces. Once you have the card fully assembled you can immediately fire it up.
At first, the new TIM did not make any difference. In fact after firing up my rig and starting cgminer with my standard settings, temps were higher than they were when I left off. Idle temps on the card were the same, but full load resulted in about 3C higher than what it was before. I thought that maybe the application of the compound had been faulty or that the TIM I used was just not good enough, but after looking into it I found that Ceramique 2 and AS5 have particular curing times. While Ceramique 2 has a shorter curing time than AS5, it is still required for optimal performance.
With this information, I decided to let my rig run at slightly reduced speed in order to let the TIM set. After about a week of running the rig and bringing it down for about 30 minutes to an hour each day, temps gradually reached a lower point.
The final temperature reduction from start to finish was between 3C-5C. Before the new thermal compound, running at memory clock 1500, voltage set to 1.09V, thread count at 2, and intensity at 13, I was getting 80C-85C on my hotter chip. After the new thermal compound, running with the same settings, I am at about 75C-80C on the hotter chip.
This makes me feel a bit more confident in letting my card run at full load 24/7. It was worrisome that the new TIM seemed to make things worse at first, but is comforting to know that there is indeed a set in period and for me personally this took about a week.
All in all, I would say that replacing the thermal compound on an HD 7990 is only necessary in certain situations that produce out of control heat issues. I think that, even with the shoddy application by the manufacturer, they still use a quality product for thermal interfacing. This was a little more trouble than it was worth, but resulted in slightly lower temps, and I’ll take what I can get.
I hope that if you decide to change out your card’s compound you have as good of results or better. Good luck, and happy mining!
If you found this article helpful or interesting, please donate a tip!