I've got a 20+ yr old Proton D540 integrated amp that I scrimped and saved to purchase back in college, and has served me well. Unfortunately over the past couple of months the left channel has intermittently gone silent. It is worse when the amp is cool, seems to go away when the amp has been used for a while. I use it in an area of the house where it is used infrequently. It also gets better when I smack the lid a la Arthur Fonzarelli. I have opened the cover, inspected the interior goods, and have used canned air to blow out any accumulated dust. All the connections appear fine, I don't see any fx on circuit boards or the like.
When the problem first started I called a local electronic repair shop and enquired about repairs. I was told it would be cost prohibitive, just buy a new receiver. I don't want that.
Anybody have a troubleshooting path I can follow?