any idea whats wrong with my amp

[thingsthatfly]

I have a marshall combo (g40 cdr I think) and ever so often it cuts out, if the reverb is on it is left with just the reverb signal and if the reveb is off it goes silent.  If I make an abrupt sound on my guitar it will cut through and the full signal will come back but if I am using distortion it wont.  Any Ideas? Its really annoying because it started happening when it was under guarantee so I sent it back then shortly after they fixed it it started happening again and it was outside of the guarantee period.  This was a few years ago and i've just put up with it but now I wanna start recording and it might cause problems.

[jbuckner]

It might be the input jack? It sounds to me that your only getting sound or a input signal some of the time.

I'd check the solder joint on the input jack and go from there.