Why does my amp do this?

[59impala]

I have a NAD C370 stereo amp. When I switch it on the sound is very weak and if I leave it alone it will build volume to normal levels after about 15 minutes. However, if I give the amp three good solid whacks on either side, it will immediately jump to full operation with no further issues.

I have had it repaired to sort this issue previously but the problem returned about a month later. They charged like wounded bloody bulls so Im not going back there.

Im thinking that there must be a simple solution. Can any of you please offer some advise?

Cheers

 

[davenn]

hi
welcome to the forums

the fact that you can give it a hit and have it come right indicates that it has some dry joints
Dry joints are solder joints that are/have failed
I would be going over the circuit board with some solder and a soldering iron and redoing some/all of the joints

Dave

 

[59impala]

Thanks...Can I tell a likely dry joint just by looking at it?

 

[davenn]

Thanks...Can I tell a likely dry joint just by looking at it?

with experience yes I don't know what your electronics repair experience is like

that's sorts why I said resolder some/all --- I would be doing some .... some one inexperienced would probably end up doing all

look at the solder joints under a magnifier ....
you may see some really obvious bad joints where the solder has literally burnt away and the component leg is just wobbling in the PCB hole.
others wont be so obvious ... you are looking for joints that look dull - "crystalline" ... ie not smooth and shiny

you mite like to take some pics of the solder side of the board
Sharp and well lit and us guys here can offer suggestions on suspect looking joints

Dave

 

[shrtrnd]

Take a look at the solder connections to your speaker output jacks,and the condition of the jack themselves.
This sounds like the problem davenn mentioned, but as long as you're inside looking around, the speaker output jacks in the amp should be looked at too.
Oxidation, corrosion, or even a worn center-pin connector might cause something like this.

 

[flippineck]

I once had someone ask me to fix an xbox - type game console. After googling the issue it turned out that most likely the cause of the problem was dry joints on the main chip.

On this particular piece of kit, the 'main chip' was a massive great big affair which soldered to the board by way of a matrix of solder pads underneath the chip. No 'legs' as such.

So the repair was done by heating up the entire board with a heat gun, after applying a non-corrosive flux.

I thought the chances of success were slim, I thought I'd just cook all the semiconductors but decided to try anyway, and blow me down it worked.

So maybe you could use a similar method.

Google "reball" "reflow" "xbox" "xbox 360" etc

 

[59impala]

I once had someone ask me to fix an xbox - type game console. After googling the issue it turned out that most likely the cause of the problem was dry joints on the main chip.

On this particular piece of kit, the 'main chip' was a massive great big affair which soldered to the board by way of a matrix of solder pads underneath the chip. No 'legs' as such.

So the repair was done by heating up the entire board with a heat gun, after applying a non-corrosive flux.

I thought the chances of success were slim, I thought I'd just cook all the semiconductors but decided to try anyway, and blow me down it worked.

So maybe you could use a similar method.

Google "reball" "reflow" "xbox" "xbox 360" etc

Thank you all for this great advise. So pretty minor problem
Cheers

 

[davenn]

it might be a minor problem ... lets hope so

report back and let us know how you progress

Dave