Last night I came across a problem I have encountered before - as the volume went up the balance moved left. I knew a defective LDR was involved, but not which one. Looking in my parts drawer I found 4 more LDRs - not sure where they came from or if any were bad, but usually I get rid of defective parts quickly. I switched out #2 (far left), deciding to just try replacing 1 at a time from left to right -I really don't remember just what that change brought about - just that things still were not right. After trying several changes I realized that I had got the LDRs mixed 
and no longer knew what was in the unit at first so I numbered all 8 and then went about trying different combinations and keeping track of the results. Now the volume goes up and down without affecting balance, but only the right channel increases when I try to change the balance - the left just stays the same. From my notes I think that positions 3 and 4 affect the left channel. Before I open the unit up again and start switching those 2 around, is just one of the (3 or 4) responsible for increasing left channel volume to change balance? It would save me a lot of trial and error if I only had to concentrate on 1 position.
Looking at the LDR3x board from the microcontroller end, the 4 LDRs at the far end are (left to right) Right_Shunt, Right_Series, Left_Shunt, Left_Series.
It's not immediately obvious which LDR or which side caused a balance shift although chances are the side it shifts towards (the louder side) is where the problem is. Or...the side which doesn't seem to track volume change normally while the other side does is also a big hint.
In terms of diagnostics, 1st step is to always rerun auto-calibration and see if that corrects the problem. If auto-cal does not complete, note which LDR it was on when it hung up during auto-cal. LDR #1 and #2 are Right_Series and Right_Shunt respectively. If auto-cal didn't hang and didn't improve things, then change out the shunt LDR on the side that's louder, THEN IMMEDIATELY run auto-calibration, and only then run music through it and see if things are back in balance. If there was no improvement, put the original shunt LDR back, replace the shunt LDR on the other side, rerun auto-calibration and do another listen. Chances are you'll be back in business at this point. It's rare that a series LDR fails but that could also be the case. You just have to try and see.
