Any idea what might be wrong with my guitar amp ?

Looking for some suggestions. In the last couple of days my guitar amplifier has started to play up. 

• I'm reasonably sure it's not my pedals to blame, the symptoms are the same whether I plug directly into the amp or whether I go through my wah-wah pedal/multi effects pedal combo
  
• I'm reasonably sure it's not my cables, I've tried a bunch including a couple of patch cables
  
• I'm pretty sure that it's not the guitar. I get the same symptoms on my Fender Telecaster, all three of my Westone Spectrums and my Yamaha SF1200. The SF1200 is affected the least - I put this down to the humbucking configuration
  

The amplifier is a 15 year old Fender Champion 110 - a solid state amplifier

The symptoms

With no leads connected, the amplifier is "quiet" with a small amount of hiss if I turn it up to 10 (sadly it doesn't go to 11).

With a lead plugged in but no instrument connected there is a a loud buzz - this has happened in the past but nowhere near as loud.

With an instrument connected the buzz is quieter but still very noticeable - I've not noticed this before.

If I touch all the strings (but not depress them) the buzz gets much quieter but is still present.

Possible causes

To me it feels like there is an issue with the earthing of the jack on the amp. 
The symptoms are similar to those I experienced with one of my guitars until I sorted out an earthing problem.

Until the formation of Wyld Bird Seed earlier this year, the amplifier had led a quiet life. It would make periodic trips to and from the loft but didn't leave the house. Now we have weekly rehearsals and have had a few gigs. I'm careful moving it to and from the car but it has been subjected to a lot more disruption in the last 6 months.

So

- Is my diagnosis plausible ?
- Are there any diagnostic steps I can take ?
- Is this kind of thing fixable ?


We have a series of gigs coming up. I'd prefer not to have to buy a new amp (not least because Mrs. Don needs a new keyboard/microphone amp as well) but I need a usable amp - at the moment this is not.

All help gratefully received, thanks

Take the amp out and give it a good clean.
A paint brush helps as a duster.

Old amps don't like dust.

Sounds like a good cleaning is in order alright. Dust can quickly overheat components and cause all sorts of mischief.

And from what you're describing it also sounds like a ground loop of sorts is developing. The pots are possibly the culprit. Just like a guitar they eventually get corroded and start shorting out. Spray 'em!

Oh, and I second that paint brush thing Damian. I use one on the bench all the time at the shop. You wouldn't believe the crap that comes in on some guitars!

Good call gentlemen, there was a small piece of the silver foil lining to the electronics compartment which had come adrift and was touching the point at which the input jack connected to the circuit board.

A good clean and normal service was resumed.

Thank you

Awesome!
I once bought a Roland JP8080 synth for peanuts because it was "broken".....a quick look inside with a magnifying glass revealed a tiny spec of excess solder touching 2 IC chip pins.
the rest is history  

I guess the moral of the story here is Open it up and have a bloody good look!