Scratching noise on volume button

[mikehende]

Hello all, I have 2 pieces of audio equipment with the very same symptoms [Numark Preamp and Digitech RDS 8000 Digital Delay], when I turn the volume knob the music cuts off and on with scratching noise, once I leave it alone the music plays fine no matter at which point the volume is. I searched the net for repair help and found this video here which shows the guy spraying the "Potentiometer"

https://www.youtube.com/watch?v=9ZxNtxOoeWA

but immediate problem I think with the Digitech Output Level knob's potentiometer if you can look at the attached pic please, seems to me the Output Level's knob Potentiometer is possibly soldered onto the circuit board? Also, I can't tell for sure if that is a hole where the red arrow is pointing, only way to know for sure would be if I could turn it somehow, any ideas please?

[nickb]

That looks like 16mm dual gang PCB mounted potentiometer. You will find them with round, flatted and spline type shafts fairly easily. Remove all the knobs, undo all the nuts and then to whatever is necessary to remove the PCB. Then you have to desolder the pot. You can try desolder braid or better fuse a desoldering tool.

[mikehende]

Thanks but sounds like a job for an experienced tech. So that won't be a hole in it where the arrow is pointing?

[g1]

Not sure if there is a hole where your arrow is pointing. But there will be a slot cut at each 'wafer' that you should be able to see in the attached picture. You can hold the unit upside down and try to get the straw/nozzle of your spray in there (bend the end of the nozzle straw).

[Enzo]

The two pots in g1's photo each have a square hole on the side. The metal side is just sheet metal, so that is a hole into the innards. If that is what is on your pot with the arrow, then yes, it is a hole. If you see something in the body of your pot that looks like a hole, then most likely a hole it is. Squirt cleaner into it and swish the control around a few times to spread it.

it is a tech job to replace the pot, but most times they clean up.

[mikehende]

The indentation in my pic has the same exact shape as in G1's image, I also inserted a computer pick into it and I would have to say yes, that is a hole. If that is the case then next step for me would be which spray to purchase. The guy is using Radio Shack Control Cleaner and lubricant:

https://www.radioshack.com/products/...-and-lubricant

What I would like to know is since there isn't a radio shack store near me anymore, what else can I use to both clean and lubricate the Potentiometer please which I might find locally? Home depot sells contact cleaner from CRC:

https://www.homedepot.com/p/CRC-QD-1...210757&cj=true

Would either CRC or WD contact cleaner do the job?

[nickb]

Thanks but sounds like a job for an experienced tech. So that won't be a hole in it where the arrow is pointing?

Seems like I'm a party of one here. I NEVER try to restore a scratchy pot with cleaner. I always replace. The only exception would be if it's some very unusual type that I can't find a emplacement for. I find that the cleaner works for a very short time and then the problem returns.

That hole looks like it will give access to only one of the two wafers. You would need a hook shaped tube to allow you to get under the pot to where the pins enter the body to spray in there.

[ric]

The indentation in my pic has the same exact shape as in G1's image, I also inserted a computer pick into it and I would have to say yes, that is a hole. If that is the case then next step for me would be which spray to purchase. The guy is using Radio Shack Control Cleaner and lubricant:

https://www.radioshack.com/products/...-and-lubricant

What I would like to know is since there isn't a radio shack store near me anymore, what else can I use to both clean and lubricate the Potentiometer please which I might find locally? Home depot sells contact cleaner from CRC:

https://www.homedepot.com/p/CRC-QD-1...210757&cj=true

Would either CRC or WD contact cleaner do the job?

I'm not a tech, but I've seized a pot up with contact cleaner. Think that's more for contacts like the old "points" in engines. Tuner cleaner might be the thing. I've found a lube i was looking for online then was able through the manufacturer's web site to find an auto parts place locally I could order it through.

[Enzo]

Oh, one can make that argument, nick, but really, a little dust gets in the pot, just clean it. If the pot is worn, then sure, cleaner won't restore it. But plenty of controls are simply dirty.

And I disagree that you miss one wafer. the wafers are at the very ends of the body, the wipers are between the two. The hole is a little closer to one than the other, but spray coats them all. These dual pots are not made like stacked pots.

[J M Fahey]

Basically any contact or pot cleaner labelled product will do.
WD40 and similar will also clean, but will leave behind a ton of oil, a greasy mess, so unless cleaning a pot backstage on Saturday 11 PM with people already getting impatient for the show to start (don´t ask), it should better be avoided.

My favorite cleaner, because it leaves no residue behind, is either kerosene (paraffin in UK?) or pure alcohol, Ethyl or Iso Propyl type.
Flood the pot through the side hole if available or through the little window where legs exit the body (tricky but doable) and as said above, move it back and forth a few times.
Then if you wish inject more clean solvent to wash away softened residue.
Place a few folded paper towels under the pot to catch the flood.

From what byou describe, pot "should" be washable.

Problem is when people does not clean it at all but swear and continue using it as is; dirt is actually very fine sand and very abrasive, in short time it will eat through the soft carbon track and kill the pot beyond repair.

[mikehende]

Ok guys, on this w/e I will get the CRC from Home Depot as it shows this below and will report back here, thanks!

Quick-drying formula
Leaves no messy residue
Used for cleaning electronics and safe for use on plastics

BUT wait a minute, now looking at this one here below, can you guys tell me which would be the better of these two cleaners please?

https://www.homedepot.com/p/CRC-11-o...5103/205021975

[mikehende]

Thanks for the help guys, I will order this deoxit:

https://www.amazon.com/Hosa-D5S-6-De...ords=deoxit+d5

When I get and use it, will report back here, thx.

[mikehende]

Hey guys, while I am waiting for the deoxit to arrive, on my Numark preamp, the only issue I was having is when I turn the volume knob the music cuts off and on with scratching noise, once I leave it alone the music plays fine no matter at which point the volume is. Yesterday however I had to reconfigure my rig this time another issue which is one of the strangest things I have encountered. The scratching knob issues on the volume control subsided and now the Bass knob has that issue instead, I am thinking then that is not related at all to the Potentiometer but rather something else on the circuit board?

[Chuck H]

There could be an issue with the circuit board. More likely you have questionable contacts where the pot lugs meet the board pads. That you have two devices doing it on the volume controls (the most used knob) is telling. So I suspect fatigue. The design trend of combining board mounting for pots and then using the pots as most of the support for that end of the board has ALWAYS been a bad idea. Yet for some reason it's VERY common. I'm not even a repair tech and I've fixed a dozen amps built like that by replacing pots with fatigued lugs, re-soldering cracked lug contacts or repairing cracked or lifted solder pads on the board. Nine times out of ten it's the input jack (if it's mounted in a row with the pots) or the volume pot that starts showing symptoms first. Because you are now having trouble with another pot, the bass pot, I suspect you have actual board/pot contact issues or board pad damage and the board will need to be removed to affect proper repairs.

EDIT:For the record, I'm all for attempting to clean the pots first as a hopeful effort. I'm just preparing you for a less favorable, and probable outcome.

[mikehende]

Got, it, thanks. I will clean all pots when I receive the Deoxit, should be any now. If still same issue I will then take to a tech for repair, get back to you guys. Meantime, how long should I wait after spraying the deoxit before powering on the units to test please?