Audio crackling - please help!

[builtclever]

Hi all,
Can anyone help me to repair the fault that is causing the crackling sound on audio please? I have layman skills, but could possibly tackle this if given instructions.
It was my Dad's unit, so very sentimental and I'd like to keep it going.

Thanks in advance.

Clive.

 

[Hajidub]

What's the unit? Most likely needs a deoxit treatment from the interior on the selector and volume pots. Spray and work them vigorously.

 

[builtclever]

What's the unit? Most likely needs a deoxit treatment from the interior on the selector and volume pots. Spray and work them vigorously.

GF767. I sprayed all pots and switches. It's not affected or caused by knobs or slider movement, merely when the volume is turned up, whether on radio tape or input.

What's the unit? Most likely needs a deoxit treatment from the interior on the selector and volume pots. Spray and work them vigorously.

 

[Hajidub]

There's a long plastic slider on the main board. This is a record switch that can gum up and affect playback. Spray the crap out of it and work by hand or record button. Any further and you're into recapping and replacing transistors.

 

[XLVII]

Hi. If I am reading post correctly, crackling occurs at higher volume levels and not when moving controls. Older radios(20 +yrs.) often need electrolytic capacitor replacement. Your output filter caps, final stage before speakers may be leaking and be far below limit leading to "clipping" when overdriven, which happens as more power is fed into system.

 

[builtclever]

Hi. If I am reading post correctly, crackling occurs at higher volume levels and not when moving controls. Older radios(20 +yrs.) often need electrolytic capacitor replacement. Your output filter caps, final stage before speakers may be leaking and be far below limit leading to "clipping" when overdriven, which happens as more power is fed into system.

Hi, thank you for replying
Yes, the crackling is there, but it's the same at all levels, not just higher volume.
e.g. If the unit is switched to tape, there is crackling even when there is no tape playing. If switched to radio, it's there at all volume levels. If switched to line-in/phono, it's the same as tape output. ‍
Someone previously suggested it could be the on/off, but I can't reason why that would be the case.
I can't post a video of the fault due to format upload restrictions.
Where would the capacitors be located please?

Many thanks.

 

[builtclever]

There's a long plastic slider on the main board. This is a record switch that can gum up and affect playback. Spray the crap out of it and work by hand or record button. Any further and you're into recapping and replacing transistors.

Thank you, I had previously tried this, to mo avail. Could you guide me through the next steps please?

Many thanks.

 

[XLVII]

Hi, thank you for replying
Yes, the crackling is there, but it's the same at all levels, not just higher volume.
e.g. If the unit is switched to tape, there is crackling even when there is no tape playing. If switched to radio, it's there at all volume levels. If switched to line-in/phono, it's the same as tape output. ‍
Someone previously suggested it could be the on/off, but I can't reason why that would be the case.
I can't post a video of the fault due to format upload restrictions.
Where would the capacitors be located please?

Many thanks.

The output capacitors are usually located near the amplifier.IC chip which quite often has a heat sink attached, making amp chip easy to identify. There are 2 identical caps, grouped together (usually) with obvious traces on circuit board leading to speakers out connector with wires leading directly to speakers.
Have you tried headphones/ext speaker jack to see if fault is present when signal goes to these jacks instead of internal speakers?
Have you tried operating the set with batteries instead of AC line?

 

[builtclever]

Thank you again. I've not tried batteries, but I did try a 12V power supply, but that didn't even power the unit.
I'll take a look for those capacitors, and maybe post a photo of them for evaluation.
Cheers.I've now tested the unit with headphones and the crackling is still evident.

 

[XLVII]

Hi. Signal to headphones by-passes the output caps we were talking about; their not the source of crackling.
Your transformer may be the problem ; failure to run on 12v might be caused by faulty/poor connection (s) and/or failing transformer.
Multimeter might reveal your problem ; check continuity on lines and pcb traces close to transformer and volts directly from transformer.
Superduper is expert in forums.

 

[Superduper]

A video showing the crackling might be helpful. You can upload it to youtube and supply a link here. Capacitors are probably a red herring distraction, they do have issues but generally do not cause crackling. I suggest you try the headphones. If the issue is not present on the headphones, you might want to consider the HA1392 output chips. This may be even more likely if you notice the crackling on the outbound speakers but not the inner woofers, as they are powered by a separate amp chip, also a HA1392. Still, while we can all take guesses, there could literally be 1000 different potential causes and if the most common ones don't address the problem, then the repair might require more diagnostic ability which is probably beyond the casual hobbyist.