CARVER 4000T QUESTIONS AND CONCERNS.

I recently bought a carver 4000t on ebay.. The person said 'like new', but when i recieved the preamp, it did not function. He gave me my money back, and told me to keep it because he didnt want to pay return shipping.
It looks great, but when i turn it on, it makes crackles, then when i push the power knob, and giggle the fuse in the back, it stops the static.
Also, none on the knobs or buttons work, it just powers on.
I took the top off and didnt notice anything odd, when i put it back on it worked for a second, the knobs and buttons all functioned. Then when i turned it off again they stopped working and havent worked since.
I wondering what the issue is because it did work for awhile. It sounds okay when the static stops, but nothing works.
I would like to get this working again! any thoughts or advice?

Welcome. Uh, just send it to me for repair/refurb. Nothing ventured , nothing gained. Could be anything, but a recap would sure narrow it down.

Get a can of De-oxit , take off the top and liberally spray all switches and controls. Let it dry and try again.

Thanks!

Ill try the de-oxit, and im sure replacing the caps will stop the crackling, but what i dont understand is,

why did all the functions work for like 30min and then stop? is there something that can describe why that happens?

now it just powers on, and when i get the cracking to stop by giggling stuff, it gives me a pure signal, from my pc to my preamp, so i can control volume and eq from my pc, and the sound is sweetened by running through this epic preamp.

but i would like all the controls to work if its something simple..

Possible misconnection or corroded connection...hence the tuner cleaner or De-Oxit.