We had a comparable problem with our TV.
There were these sparkles coming out of the back, along with a bit of smoke (note, this tv is MY age, and I'm turning 19 next week, so...), so I've shut it down asap.
And ever since, (this is gonna be a bit hard to explain), the images on the tv go wider, they even exceed the frame, so while you would have this:
[ ] being the TV frame
(.Y.) being the images
Normally you have this:
[(.Y.)]
But we have this:
[.Y.]
But it still works. Beat that new generation technology!
Now, back on topic, I'm gonna say listen to Slanderous, if you still have warranty, I'd take it to the repair center. If not, I'd ask if somebody could give you a price for howmuch it would cost to repair the amp.
But yeah, as for our TV, it would cost about €130 to fix it, but it's not worth it, 'cause of the age. But maybe your Marshall is worth the cost.