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Crackly volume pots on a 120w combo. How to fix?


stefBclef
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Hello all

As the title suggests, I would like to know if the crackling pot is something that can be fixed, and how easy it is to do. It's not my amp, but one I am considering buying as I am looking for a cheap combo to leave in a rehearsal space. Apparently, as well as crackling, the signal cuts in and out when you adjust the volume pot but is fine when you leave it at one level.

[b]My questions:[/b]
[list]
[*]Does this kind of fault usually develop into a more pronounced fault, maybe even to the point when it crackles and signal cuts when you are NOT adjusting the volume pot? OR does it tend to only be an issue when you are adjusting the pot level?
[/list]

AND
[list]
[*]How may one go about fixing this issue?
[/list]

The details I know about the combo is that it is a 120watt Laney.

Many thanks everybody.
Stef

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Two reasons for this to happen:

1. Dirt inside the pot - buy a can of contact cleaner from a electronic shop and spray a couple of times inside the pot;

2. Busted pot - find out the pot's demensions and resistance, take it out and solder a replacement;

Each of this require you to remove the head from the combo and have a bit of electronics knowledge if you have to replace the pot. If you don't know how to do this i sugest you to find someone who can help you. Both are easy and cheap fixes.

Cheers

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As above. Worst case is a pot replacement, a pretty simple job if you can solder, but a squirt or two of contact cleaner would definitely be the first thing to try. This is the stuff I keep on the shelf: http://www.maplin.co.uk/contact-cleaner-4153

In either case the amp will have to be opened up to access the pot - again, a simple job if you're sensible and take care.

I'm not sure about professional repair costs but even a pot replacement shouldn't take more than one hour, so maybe £25?

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Ok, I got my hands on the amp and, after wrestling with it for half an hour, I got it sounding pretty damn nice so I am happy. It then played nicely for the rest of rehearsal (2 hours or so).

Some description of the symptoms:

The pots are more than crackly. I would describe the sound as more of a rumbling storm that's brewing and occasionaly gets really loud and then dies down. The sound then cuts out at times and comes back when you turn the dial (although not consistently in terms of the position of the dial).

This is the same on both pre and power amp pots and also on the treble pot. There is also some horrible loud noises when you so much as touch the input jack. Both active an passive jacks seem affected by the same problem.

So...

When I get the chance I will open it up and have a clean with the contact spray as suggested above.
[list]
[*]Is there anything in particular I need to be careful with when opening the amp / touching the circuitry or anything? I don't want to damage it further you see. I can solder but I am deffo an amateur!
[*]Do these symptoms suggest something different might be going wrong? The fact that its affecting so many parts makes me think that maybe there is something else the matter. Someone mentioned it might not be earthed properly...plausible?
[/list]

Thanks a bunch all y'all
Stef

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Think that sounds a lot like solder joints loose, especially the jack touching part, which is easy if you can solder, but the randomer pot noise might be a leaking capacitors putting dc across them, which you have to poke about with a meter to find and replace, spray and solder first to make sure it isn't easy things.

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Before you start opening it up it might be worth simply whacking a jack lead in and out of the socket over and over again.

Then flip every rotary control back and forth repeatedly.

It's amazing how sometimes a head can just 'lock up' in certain positions if it isn't used for ages or is simply left with every control pot in the same position.

TBH it sounds like it needs more than this but it's worth a try anyway :)

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  • 3 weeks later...

Hello again,

I am going to get round to opening this combo up this weekend, and hopefully fix the problem. The amp is actually at my friend's house so I would like to try and find out more or less what I might need so I can take it round.

I will start by giving it all a clean with the contact cleaner recommended above. The contact cleaner came with a nozzle, do I also need some kind of cloth to wipe away excess fluid or other dirt/dust? If so does it matter what type of cloth? (e.g. lint free, yellow duster jobby etc.)

Then I will look for any loose solder joints and solder if neccesary.

I am expecting to have to replace the volume pot as it is more than just crackly, it cuts out in most positions. Is this the type of pot I can expect to see in there? [url="http://www.maplin.co.uk/standard-dual-gang-potentiometers-2207"]http://www.maplin.co.uk/standard-dual-gang-potentiometers-2207[/url]

Hmmm what else; oh yes, is there anything I need to be careful with so as not to cause further damage to the amp while rooting around?

Any other advice you can think of would be appreciated and i'll let you know how I get on.

Ta
Stef

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Take around the contact cleaner and a soldering iron and some solder. If you can't fix it with them, you'll need a new pot.

First of all give the pots a good wiggle, roll them up and down and try unplugging and re-plugging a jack lead several times, sometimes that works out the muck that might've built up.

Try contact cleaner first, it doesn't really matter what you wipe any excess away with as it's what goes into the pot that's important.

If that doesn't work, wait a while for it to dry fully then you could try re-soldering the contacts on the pot.

If that doesn't fix it, then you'll probably need new pots.

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[quote name='flyfisher' timestamp='1338469541' post='1675049']
...a squirt or two of contact cleaner would definitely be the first thing to try. This is the stuff I keep on the shelf: [url="http://www.maplin.co.uk/contact-cleaner-4153"]http://www.maplin.co...ct-cleaner-4153[/url]

[/quote]

Ok, I had a go at fixing this, and I am a very happy man! Turns out all it needed was some cleaning with the contact cleaner and the pots are now working perfectly. Also the input that wasn't working has also come to life after jamming a jack in and out and blowing it.

Great advice BCers! Thanks a bunch.
Stef

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