I have just built a tubescreamer using the Tonepad circuit and board. I have two problems. Firstly the tone control does not seem to be doing much. I am using a 25k pot for tone instead of a 20k.
Secondly, the amount of volume boost that i am getting seems to be negligable. I have to have the volume turned up all the way to match the level of the amp when the pedal is turned off.
As for the tone - it is excellent. I have been accidently supplied with a 250k gain pot - I dont know whether this is contibuting to any problems
Those tone and gain pots should be ok (tho you'll miss out on extra-high gain with 250k - a 1M pot is a better substitution for the 500k).
You should be getting a major volume boost when turned up. And the tone control should be doing quite a bit, too.
An "audio probe" (as described in other threads on the forum) is useful for determining where you are losing signal volume. Otherwise, it a slow check of all components for values and soldering.
good luck