Fixing a hi-fi

[d000hg]

Have a oldish, reasonable Hifi, as separates... actually only using the core amp now. It has developed an odd fault that when you turn it on no sound comes out. If you start it playing something then a few minutes later you get a very quiet level appearing from one or both speakers, which gradually (or in little jumps sometimes) increases to where it should be based on the volume.

I initially thought it was just broken or the speaker cables were to blame, but swapping the speakers round and jiggling them shows it's totally consistent, no intermittent connections there. Similarly, the volume knob doesn't act erratic.

This weird "warming up" behaviour, what could it be? Why would a modern bit of kit do this, not like it's got valves?! Loose connection maybe inside, or a dry joint?
The system was acting as our TV external audio but has been relegated as my PC sound now due to the problems. I can't really justify to myself buying proper hi-fi separates for my PC but if I can get it working it's SO much nicer than crummy computer speakers, and then I can buy something new for the TV.

[gingerjedi]

Have a oldish, reasonable Hifi, as separates... actually only using the core amp now. It has developed an odd fault that when you turn it on no sound comes out. If you start it playing something then a few minutes later you get a very quiet level appearing from one or both speakers, which gradually (or in little jumps sometimes) increases to where it should be based on the volume.

I initially thought it was just broken or the speaker cables were to blame, but swapping the speakers round and jiggling them shows it's totally consistent, no intermittent connections there. Similarly, the volume knob doesn't act erratic.

This weird "warming up" behaviour, what could it be? Why would a modern bit of kit do this, not like it's got valves?! Loose connection maybe inside, or a dry joint?
The system was acting as our TV external audio but has been relegated as my PC sound now due to the problems. I can't really justify to myself buying proper hi-fi separates for my PC but if I can get it working it's SO much nicer than crummy computer speakers, and then I can buy something new for the TV.

Look for bulging or leaking capacitors (the cylinder shaped things) they should be flat on top, easy to source and replace.

[Spacecadet]

This weird "warming up" behaviour, what could it be? Why would a modern bit of kit do this, not like it's got valves?! Loose connection maybe inside, or a dry joint?

It will be a broken solder joint somewhere. Thermal expansion will fix it whilst it's hot!

[Paddy]

It will be a broken solder joint somewhere. Thermal expansion will fix it whilst it's hot!

You will need.
PCB Cleaner.
Flux Pen
Soldering Iron
Soft solder

Take out the PCBs and clean them.
Use the flux pen to wet every solder joint and gently touch each joint with the hot iron so that the solder flows. If needed add some solder. It has probably failed on one of the components that gets hot.

[Spacecadet]

You will need.
PCB Cleaner.
Flux Pen
Soldering Iron
Soft solder

Take out the PCBs and clean them.
Use the flux pen to wet every solder joint and gently touch each joint with the hot iron so that the solder flows. If needed add some solder. It has probably failed on one of the components that gets hot.

Or buy a new amp

[d000hg]

Shame to buy one for £100 if 10min might find something obvious.

[The_Equalizer]

Or buy a new amp

Indeed. I love second hand hi-fi bargains. I bought myself a jolly nice Marantz number a couple of Christmas ago when I made a few bob from a sideline. I think it was something like £2500 new and I got it for £420. Magic amp. Then again, getting your current one fixed shouldn't be too hard and a bit cheaper.

[Paddy]

Or buy a new amp

Cleaner £6
Flux £7
Solder £3
Iron £20

Yes; buy a new amp on eBay!

[d000hg]

Hadn't thought about 2nd hand, though I don't really like buying heavy things on eBay. But tools and so on I have or could borrow, the only cost is my time so a few minutes is ok, but much more and it's cheaper to just buy.

If I open the amp up, how long after turning it off should I wait? Is it useful to do it while still warm, or should one wait several minutes to avoid charged capacitors?