**CRT Warning** don't work on a CRT without experience and know-how of proper precautions. They can kill you. (That's the disclaimer)
Those kind of issues are almost always related to a capacitor problem. Try leaving it on without a signal plugged in and see if it does the same thing.
If it does than it is very very likely a cap issue. If it doesn't, then you have an issue related to the signal processing circuitry probably, and should inspect signal levels going into the jungle IC.
The schematics for these are readily available but it will take some work to track down the issue. Start with a visual inspection of all the large caps around the power supply to see if they are bulging and then replace the obvious large coupling caps.
-Segasonicfan
