I wanted to contribute and explain how I was successful, after having the same issues as you. I have two practically new XFX 7850 Ghost/Core series 1GB cards, and these things are finicky as heck! Wow (insert doge meme). I could not get these to run scrypt at rates anywhere close to what is shown online (under 230 kh/s... similar to my 7790s) and any time I dial up the intensity or clock rates, the hardware errors would pour in, making hashing with the card worthless... The cards are stable, and run great in gaming, even with an overclock, but I could not get any settings to work on these to get any meaningful hashrate.

Well I was successful at getting over 320khs on each card when doing my first tests with them for a short period of time with these settings (i am not typing the obvious parts of the config):
--intensity 17 --gpu-threads 1 --gpu-engine 1100 --gpu-memclock 1200 --shaders 1024 --thread concurrency 8000

However, once they got warm, and over time, I started getting errors any time I try to go back to those settings... In addition, in one desktop, I was running a card that needed to run at a gpu threads count of 2. I figured all hope would be lost...

Then I began fiddling for a good long while, and if let the 7850 run at 2 gpu threads, turned down the intensity and thread concurrency, I actually could get meaningful hashrate. If I turned up the intensity one more to 13, I would get HW errors out the a-... places. My hashrate collapsed hard when I would set the thread concurrency over some number around 6000. It appeared that underclocking and overclocking both the core and memory would not cause hardware errors unless they are too extreme. Clock rate will vary by model of 7850... stock clocks should be great, and if you can get close to your max overclock, it can be even better.

Therefore, along with a 7900 series card as a display card, with 8GB of memory on the desktop, I was able to tune the 7850 with the following settings to get over 360khs on this desktop, and another 7850 (by itself) to run at 380khs, all without hardware errors:
--intensity 12 --gpu-threads 2 --gpu-engine 1050 --gpu-memclock 1200 --gpu-vddc 1.1500 --shaders 1024 --thread-concurrency 4096 --worksize 256 (dont just copy paste in case i mis-spelled something)

I ran the 7850s anywhere between 800/1100 and 1100/1200 with success, but the limiting factor was noise or heat (the heatsink on the Ghost/Core series XFX are dismal). If the intensity is changed to 13, you get hardware errors. I think that you may be able to get a thread concurrency of just under 5200 to work as well. I used numbers from 5120 (1024 x 5) to 5192 (8192 and changing 8 to 5 haha) while fiddling and <5200 is all I can remember. I think values too low (3072 or so) will cause hardware errors as well, and numbers over the mid 5000s will cause the hash rate to collapse hard. I tried a worksize of 128 but the changes might have been within the magnatude of error but the worksize could be worth tweaking. The voltage is not needed, but I tried it to see if it helped with both overclocking and stability of the gpu. Stock voltages are like 1.1380V, and 1.1500V isnt a big increase. I didnt see any gain using a voltage of 1.1750V either, so changing voltage is up to you... oh and yes even on this limited model, cgminer was able to adjust the voltage no lower than 1.1380v and i didnt try above 1.1750v. I confirmed this change in GPU-Z.

Oh and I am using cgminer version 1.7.2 and the Catalyst 13.9 version. If you see the power tune set to 3 (3%), it is because of a weird powertune bug that older versions were plagued with that make it where any number in the range of 0-1,4-20 (approximately) caused one or both cards to not switch to full clock speeds and stuck in its low power and frequency setting. You can use the powertune values that worked for you already, but 3% is a nice and safe value (and 20% doesnt unlock any more performance on this card, nor any stability).

I wish you luck. I am still fiddling with the cards. I could not get over 230khs with the threads set to 1 without a ton of hardware errors, regardless of intensity, clocks, thread concurrency, but I found a nice compromise in switching to threads of 2... thank you 7900 series card for forcing me to fiddle and find a solid hash rate! If you have any questions about settings on the 7850, feel free to PM me any time.

Cheers,
-Tony

EDIT: By the way, the desktop with the 7970 in it and the 7850, I have 8gb of ddr3 ram and no SDK pack installed. I get around 360-ish khs on that PC... The other motherboard where I am running the other 7850, I have a heavily underclocked dual core CPU and only 2GB of ddr3 ram and I get 380khs! This is great since I had the same exact issues as you until now. On either PC, a thread concurrency of over 9000 (lol) would not start... However the exception is when you turn the gpu-threads to 2 and lower the intensity to below 13. The only card running at 16384 tc is the 7970.. the others run funny at 8192, so I run them at 8000 (a sweet spot!)... regardless of system with 8gb of ram or 2gb... When I run a threads of 2, I use 4096 (even with 7790s if I had to run at a thread count of 2). I feel like the odd one out where I have 8gb of ram and I cant do a high thread concurrency like all tutorials and folks say. I just ignore that and use 8000 for a threads of 1 and 4096 for a threads of 2. I do keep trying different values with the same confirming results, so I am not stubborn and habitual with my cgminer settings, just thorough haha! Peace.

grytigbcm

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