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Flextone II HD: Left Channel Dropping Out Intermitently [ SOLVED ] My LEFT SPK CHANNEL was dropping out more often than not & thought i had a CAP or TRANS issue, but found the LIVE/STUDIO toggle switch in the back was simply oxidized/dirty. Spent about an hour inducing/resolving the problem to narrow down root cause & solved it with Electronic Contact Spray (go easy with it yo!) The front knobs were mentioned several times, but didn't come across this issue/root cause so figured I'd drop a note on quite the serious problem with an equally simple solution. Picked up one of these units a while back for its stereo capability and on the first go at it, the Left Channel was "hotter than Georgia pavment" then slowly faded out to about 50% so stuffed it off in a room for about a year & now finally getting back around to loose ends. Parsed boards and excluding component failure, the 'pots' were often brought up as root cause to volume problems. Given they are analog front-ends to digital functions, 'scratchy pots' can cause wild swings in the values they induce to the logic boards. My particular issue didn't really match, so sat with the unit for about an hour to create the problem, solve it, create the problem. Triage: Powered down amp and swapped the speaker cable between LEFT & RIGHT and adjusting the front knobs and changed 'channels', FX, cabs, etc. - wasn't telling me much Moved on from A/B comparisons and stuck with the LEFT problem child channel Originally thought it could be week PCB traces or solder joints since it worked for about 3min when I first powered it up. Toggled the Speaker Ohms toggle from 4-8-16 several times - no help. Since the channel came back to life intermittently, went ahead and sent the XLR outs to a mixer to monitor with headphones. LEFT still had issue Swapped LEFT/RIGHT XLRs & problem followed the LEFT XLR cable. Deduced issue was NOT with the POWER AMP ( which was my original thought ) Ran TRS from FX SEND to RET no change Went ahead and pulled the head out of the chassis and found duplicate boards in use for LEFT/RIGHT paths, so swapped the to I/O ribbons off the MAIN PCB Issue STILL on the LEFT CHANNEL swapped the I/O ribbons to their original orientation. Before diving in to look at components, sat with it for about 40m recreating/fixing the issue I noticed that if I MAX'd each knob for full volume, the LEFT channel would be inclined to eventually come back to full strength. Was still suspecting the POTS, but it really didn't seem logical that controls that impact BOTH channels could take out only one channel - was musing perhaps a POT leg was shorting or creating some other ground issue. The root cause was found when taking another look at the back & found the LIVE/STUDIO toggle switch. When I touched it, the familiar scratching sound ushered forth and after jiggling it around delicately I could kill & resuscitate the LEFT CHANNEL. I dropped the MIDI/XLR board out and gave it a quick spray of Electronic Contact Spray, worked in for about 30s, reinstalled and SOLVED. Hope either the diags or the root cause / solution helps someone else!