Reading of the voltage of one phase feeding the GPU
Here is the localization of the different voltage measurement (or v-check) points on the Radeon HD 6870 PCB (back side):
Radeon HD 6870 voltage check points (2 pictures total)
VDDC is the GPU core voltage (there are 4 x 2 points because 4 phases feed the GPU). MVDD is the memory voltage and (correct me if I’m wrong) VDDCI is the I/O bus voltage (between memory and GPU core) and comes from the PCI-Express slot.