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Scratchy Volume Pot

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Hi Guys,

Just wanted some opinions/advice on this:

My Hartke LH500's volume pot has started to become a bit scratchy, so much that's is causing the cab to hiss when it's turned up. It's not just happening when adjusting the volume either, it's a constant scratch/crackle.

It's not a massive problem but when playing, but I'm a bit worried it's going to get worse or start to cut out or fail altogether!

Does anybody know if this will be an easy fix? A massive issue? OR worth getting it serviced?

Thanks in advance.

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Most likely a simple fix.. http://www.themusicroom-online.co.uk/product_info.php/products_id/2750
Servisol is one of my must-haves in the toolkit; I even rescued an amp one time!
Bring the bass down to the shop in Cleckheaton some time and we'll give it a check over to make sure.

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Thanks hubrad, I'll give it a go! I'm guessing this will involve taking the case off? (Forgive the naive questions!). I might take you up on that offer of having a look at it!

Cheers

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You need to gain access to the back of the pot. Usually all the screws are in pretty logical places. Squirt Servisol into the back of the pot and give it a wiggle back and forth. Repeat a few times.
If that doesn't work you're into amp repair territory.

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[quote name='AnalogBomb' timestamp='1359372524' post='1953581']
I'm guessing this will involve taking the case off?
[/quote]

Remove the 10 or so dinky little screws from the top panel, and it lifts right off. Prepare to be amazed at how little "stuff" is in there.

Once you're in, the pots are easy to get at as I recall - just poke the flexi tube into a gap in the pot casing, and give it a squirt. Repeat as necessary.

While you're in there, you might want to make sure that the valve is seated properly, just in case that's contributing to the noise.

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I can't comment on your exact amp/experience, but my volume pot is opposite the fan on the back of my amp, which blows dust directly at that pot. I just had to replace it when it was serviced, they are pence to replace 9 times out of 10..

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Hey guys / girls 

My LH1000  had a very bad scratchy ,crackeling sound from the volume pot  two things l did ..clean the volume pot and replace the preamp tube ..FIX ! 

Love this Head lots of power and clearity ! 

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Use the TINIEST amount of cleaner, less is more in this case. In the US, DeOxit D-5 is the only substance that I have tested extensively with no long term (over 20 years) issues. I do see a lot of pots for units in for service that were cleaned with a variety of "miracle cure-all sprays" that have subsequently become ruined (either from the product, or from over-application which washes incompatible lubricants into places that causes additional damage). 

I do not know if there are equivalent products across the pond, but based on what I have seen acceptable products are few and far between.

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On 05/11/2020 at 11:17, MOSCOWBASS said:

DeOxit 5 is available in the Uk. I have some, bit it's not cheap!

Yes, often "not cheap" goes along with very good.

A little bit goes a very long way.

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On 05/11/2020 at 19:04, agedhorse said:

Use the TINIEST amount of cleaner, less is more in this case. In the US, DeOxit D-5 is the only substance that I have tested extensively with no long term (over 20 years) issues. I do see a lot of pots for units in for service that were cleaned with a variety of "miracle cure-all sprays" that have subsequently become ruined (either from the product, or from over-application which washes incompatible lubricants into places that causes additional damage). 

I do not know if there are equivalent products across the pond, but based on what I have seen acceptable products are few and far between.

Thanks for this information Andy. I've just ordered a 5oz aerosol can of D5 (£22.95/$30 delivered) but wonder how best to apply a tiny amount into potentiometers? My experience with this type of aerosol with the thin tube is that a quick press of the button still releases a pot flooding amount of fluid; or maybe the D5 can is better? Thanks again. 

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If it's the can that comes with the small removable tube that sticks directly into the nozzle it's not to bad, but the new style with the swivel is a real pain and you have to have just the right touch. Also, NEVER spray down the shaft (no matter what you might have seen on the internet). That's a quick way to ruin a complete set of pots as it washes the bushing lube everywhere it doesn't belong.

I see units with spray residue all over the PCBs, and this attracts little conductive bits that then provide leakage paths. This is especially true on circuits with very high voltages and also very high impedances. Once this happens, the PCB must be removed and washed in an approved solvent to remove the oily residues. Then the usual production wash in a saponifier with a DI or distilled water rinse and mild temperature (like 120-130 deg F) bake dry. Pots and switches (and anything that can't be washed in production after wave soldering) must be protected. Different parts have different requirements, which is why I try to avoid this and when it happens it's costly to remedy because it takes a lot of time to do right. In my shop where I still service Genz Benz products, I know what parts are safe to wash and what aren't, but even then it adds between 30 minutes and an hour to a repair. It's one reason why I discourage DIY repairs, they are MUCH harder to correct and repair right. The other reason is that we have to examine the amp closely for any additional, hidden repairs that may jeopardize reliability in the future. Everything that goes through our shop carries a 90 day service warranty and I don't want to see any repairs back because I missed something. Generally I can keep it to one or less service re-work per year because of this policy.

Hope this helps.

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Thanks Andy. It's the new swivel type I believe. I'll be using it to hopefully improve scratchy pots on a passive p bass so no real voltages or pcb tracks/components to be affected. I think I'll try spraying some into a bottle top then use a small pipette to apply it.

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I have not used DeOxit D-5 but have used Servisol Super 10 for years.  As for the fan propelling dust into the pot, I would appreciate @agedhorse comments  but I was always told that much of the "dirt" in pots comes from wear on the tracks. I must admit though that in my early days, fans were few and far between.

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Generally, IF THE POT HAS NOT BEEN CLEANED WITH "MIRACLE CURE-ALL" CLEANER, dust is not a problem with the rotary pots. What can be a problem is microscopic insulating layers of oxides and sulfides that are angstroms thick, just thick enough to inhibit reliable contact with the fingers of the pot's wiper element.

DeOxit D-5 in particular is quite effective on this without damaging the conductive element (especially at the terminal rivets), but liberally applied will wash the lubricants from around the bushing onto the conductive track which will attract abrasive debris and grind the track and fingers into oblivion. 

Other substances can do this as well, but also damage the conductive surface, making it MUCH more vulnerable to wear. Some techs refer to such substances as "disaster in a can", because when they work on amps that have been serviced this way, they often can become disasters. A full set of pots on some amps can push the cost of repair beyond the realistic market value of the amp. 

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£22 on some deoxit spray or £10 (maximum) on 2 new pots and ten minutes to solder them in...?

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54 minutes ago, paul_5 said:

£22 on some deoxit spray or £10 (maximum) on 2 new pots and ten minutes to solder them in...?

Assuming that no new damage is created. That's another topic, but I see folks try to do this kind of repair and damage otherwise perfectly good PCBs because they don't have the proper tools or experience to work on double sided PCBs (the norm now).

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3 hours ago, paul_5 said:

£22 on some deoxit spray or £10 (maximum) on 2 new pots and ten minutes to solder them in...?

On a 61 P bass....?

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9 hours ago, Sparky Mark said:

On a 61 P bass....?

I don't understand your point. Are you saying that

Quote

£10 (maximum) on 2 new pots and ten minutes to solder them in...?

Is wrong?

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I'm saying that replacing rather than cleaning pots on a pre CBS vintage P bass will reduce its value, possibly by several hundreds of pounds. £22 suddenly isn't so expensive.

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1 hour ago, Sparky Mark said:

I'm saying that replacing rather than cleaning pots on a pre CBS vintage P bass will reduce its value, possibly by several hundreds of pounds. £22 suddenly isn't so expensive.

Granted, but this thread is about a Hattie bass head, not a vintage bass guitar.

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On 10/11/2020 at 14:43, paul_5 said:

£22 on some deoxit spray or £10 (maximum) on 2 new pots and ten minutes to solder them in...?

Ah Paul! You make it all sound so simple! LOL

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