Popping Sound JCM900 4102

[norby3]

So I got a little bit logical about this and decided to follow an approximate path through the circuit. There was/is some black stuff on the terminals of the power transformer on the red and black terminals, though they don't look totally smoked like a resistor might. Differentiating between burns and corrosion on solder is what I needed to do. Anyway a couple of the terminals (B+ I believe) on the tube sockets also look a little carbony but not overly so. What I thought was a little brown discoloration looks more like deposits. I scraped a bit on the power transformer terminals and the stuff came off like you'd find on a burnt chicken leg.

I don't know what the root cause yet. I think I'm correct in my analysis however, but I'm still learning about this stuff.

[MikeH]

The flash does weird stuff...the joints are firm and shiny, but not beautiful. In fact, the soldering job the manufacturer did on this is far below my standards.

Now that you've isolated the problem to the power section, I'd start by cleaning up/reflowing the joints in that area. Actually I'd start by chopsticking the area to see if you can isolate the problem. My "Chopstick" is a narrow rubber stopper with a dowel rod fitted into it. With the amp running, tap on the components in the problem area and see if you can recreate the pop. Make sure you tap on any connectors (like the 4 pin, 6pin, etc. connectors that connect the boards together - I've found those to cause crackling due to loose connections or corrosion). If nothing specific shows up, then I'd try cleaning up all of the joints.

[g1]

As far as the output fuses, power down when removing or installing.
The black stuff you are describing sounds like solder flux. It can get very dark, almost black looking depending on how much heat is applied to the joint.

[soundguruman]

So I got a little bit logical about this and decided to follow an approximate path through the circuit. There was/is some black stuff on the terminals of the power transformer on the red and black terminals, though they don't look totally smoked like a resistor might. Differentiating between burns and corrosion on solder is what I needed to do. Anyway a couple of the terminals (B+ I believe) on the tube sockets also look a little carbony but not overly so. What I thought was a little brown discoloration looks more like deposits. I scraped a bit on the power transformer terminals and the stuff came off like you'd find on a burnt chicken leg.

I don't know what the root cause yet. I think I'm correct in my analysis however, but I'm still learning about this stuff.

"A little carbony"
even the slightest trace of carbon can make it arc...in a variety of places...
It would be helpful to post some pictures.