K2015 THD board usually isn't too difficult to fix, I fixed a couple of broken ebay cheapies some time ago.
Find the data sheet for all chips (AD9850, OPA275 and a couple more, follow the signal from AD9850 towards the BNC, the area with the analog switches is a bit confusing, those 2x4 opamps on the bottom are used to buffer the signal on each BNC, each opamp has 200Ohms on output to get 50Ohms on BNC).
One of mine had a bad OPA275 and another magically fixed itself after swapping a couple of chips. It's also very helpful to have another working K2015 next to broken one, so you can compare signals, exchange those 17AT65 EPROMs to confirm data integrity and swap suspect chips, so you don't have to buy them only to realize the problem is somewhere else ;-)
I have uploaded 17AT65 firmware here on forum, in case you need it.