4780 chip amp problem

[littlerick]

Had my 4780 amp running for just over a year and has been sounding great....However, it has now got a loud deepish hum that comes from speakers at quite a volume. It doesnt get louder or quiter when i use volume control.

Another thing I have noticed is the LED seems to take a while to fade after power off.. not sure if it has always done this, but I noticed it when i was trying to figure the hum.

Any help would be great thanks.

[AndrewT]

Can you measure voltages, both AC and DC?

[littlerick]

No.. I have no multimeter.

[AndrewT]

What resources do you have, that might be of use in trouble shooting?

[littlerick]

I have an electrical screwdriver and a soldering iron.

lol, im not much help to myself realy am i. I was gonna rip it apart and rebuild it, however that may be a little extreme if its a simple problem. You guys are always helpful, so I thought i would take the safe route before being a butcher.

[AndrewT]

Soldering iron, some thin copper wire (0.1mm to 0.6mm diameter), some flux cored solder and a redundant RCA plug gets us started.

Can you gather that together?

[littlerick]

Yes I can get that together... However, my grandson is gonna be here in 10 mins and that is the end of my day. I will be back online at about 8pm, when hopefuly the wild little terror will be asleep. So I apolagise in advance if I dont reply to next post until 8ish... He's a great kid, he's faster than my bloody kawasaki.

[KatieandDad]

You really need to source a multimeter. Beg Steal or Borrow, they're not expensive.

An LED taking time to die out can be a good sign. Depends on the circuitry around it.

[AndrewT]

Solder a tiny length of thin copper wire from Hot to Ground in the RCA plug.

Remove the power from your amp.
Remove ALL leads, cables, interconnects from the amp.

Attach one speaker only to one channel.
Plug in the shorted RCA plug into the input of the same channel.
Power ON.

Has the hum gone, or less, or more?

Power OFF.

Now swap the RCA shorting plug and the speaker to the other channel.
Repeat the Power ON test.

Report your results when you can, someone will be listening.

How did the kwacker get bloody? Did you drop it?

[littlerick]

Woot.. grandson asleep now....OK... Unable to do the above until saturday evening at best... Wife will cut bits off me if i wake grandson, however i have managed to borrow a multimeter off a friend.. I'm hoping there may be a way to test it without losing bits i may need.

Oh by the way... I have no idea what settings on this dial i need or where i gotta stick the rods... Yes I realy am that new to this stuff.