Intermittent Problems

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Intermittent problems are some of the most frustrating ones to solve. The amp works fine until - something - happens, and then it acts up. Most of the effort in debugging this one is to make it act up so you can cause it to happen when you want, which will then in turn let you find the problem, and verify that you have really fixed it. Intermittents always mean that something is just at the very edge of failing and it takes the causing event to push it over. When the causing event or condition is not present, it works fine, or maybe will "reset" when the amp is turned off or cooled.

Notice carefully what makes the intermittent happen, if you can. Very common events that institute intermittent problems are:

This one is probably only going to yield to the laundry list technique, so here goes:

Depending on how desperate you are, you might want to apply a shotgun technique: Methodically remelt every single solder joint in the amp, adding in a bit of rosin core solder as you do. A milder form of this would only remelt the ones in the circuits you suspect. This sounds horrible, but really doesn't take all that long. The worst part of doing this is that you never really find which one caused it, just that the problem quits.

I have a friend who repairs amps for a living and who said he once fixed an intermittent problem on a Fender where the amp was cutting out intermittently. He found that the wires to the output tube sockets had been put in the correct places but never soldered!