Randall RG 170 ES reverb problem-HELP!

Hello Group,

I have had this head for the longest time & it seems that the reverb on it has gone out.At 1st I thought it might be a footswitch issue so I tried another.Both footswitches change from clean/crunch but the "reverb " button is not kicking in the reverb.When I turn the knob from left to right,I hear a slight crackling noise but no sound difference (no reverb).

I know that this amp is old but it has become part of the "family" you can say.Before I take it to be "serviced" & spend a bunch of money (I'm tapped out cause of the holidays),I am hoping for some input from someone in the know.If I can possibly get it to kick in on my own that would be great.Any help will be appreciated!