Marshall Support

need component layout for this amp

I recently took the amp out of storage and now when I plug a guitar into the transducer I get no out put. Could the input be faulty or is the whole second amp shot? Or could it be a bad fuse or tube?

How do you tighten the loose input jack? It is loose on the inside.

I have a JCM 800 Series 50W 4104 2x12� valve amp, I have had it since new and probably played it 30 times over 20 odd years ( Never been touched), the amp is as good as the day I got it, however I only play it at very low volume, I have the Pre amp volume knob at ¾ and the master almost to the 1 mark. And yes I know that�s really low and why buy a Marshall if you aren�t going to crank up the volume! I have always wanted One ! The problem is when you have been playing for 45 min to an hour the volume starts drop and crackle ( Low thunder type noise, No Lightning though) like a noisy volume knob with moisture in it, If you leave the guitar sitting there silently you can hear the noise or humming fluctuating sound quite clearly, if I turn all the knobs it doesn�t change or stop the noise. Wiggle the guitar lead jack�s doesn�t help, I have had it serviced and as expected the original valves were as good as new and not replaced, bar one 12AX7. A dry solder joint on the master volume pod was thought to be detected and re soldered however noise still there. I have tried new guitar leads, Several different guitars, both High and Low gain inputs doesn�t make a difference. Has anyone had a simular problem so I could let the repair man know where he might need to look? the repair man i use is very good its just this faul is Intermittent and hard to track. I am at a loss!!! Help Regards Tim