A while ago I built the blues buster for a friend. Fantastic pedal. A few days ago he returned it to me indicating the gain control does not respond. I have tested this and he is right, in any position it retains the same sound (not completely off, not completely on, don’t have working version for reference so hard to judge). There seems to be a slight diffference in volume when I turn the pot from one side to the other, but nothing audible when playing.
Ofcourse I checked with a new pot: same stuff. Measured resistance on pot leads: goes nicely from 0 to 250k. I’ve replaced the IC too, to no avail.
One thing that struck me is that the voltage on lug 6 is at a stable level: VB (around 4.5V). Is this supposed to be the case? Or should this change with the gain pot position?
Any advice to in which direction I should look for the solution? I have checked a few point around the gain pot with an audio probe but I cannot do it at meaningful levels because of neighbours: will report when I get a chance to do this.
I can only guess with what I have to work with so my best guess is he dropped the pedal on the ground and ruined something my first guess also being the pot. Another popular thing people do is swap chips and can easily mess things up past the diode protection. I have had that happen more than once and now I will always tack solder a chip in place so they can’t switch it. Also make sure the chip is properly seated as well. I would be using an Audio Probe along the entire audio path to see where your problem lies very quickly.