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Scratchy pot not coming clean

socrates75

socrates75

Well-Known Member
Pioneer QX-747, blasted all the pots with deoxit and it worked great, but then a few days later the volume pot starts getting scratchy as soon as i turn it on, turn the volume up and down and it scratches and pops so i turn off the speakers and turn the volume up and down for about 10 to 20 seconds and it clears right up.....so i pulled the whole beast apart again and blasted the volume pot again, this time i have almost gone through the whole can of deoxit, put it back together and it worked great again but for only a few days, and im back to square one now, so when ever i want to use it i have to turn off the speakers and turn the volume up and down a ton just to clear it, is it volume put broken or is it so dirty that im just mushing the dirt around?
 
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socrates75 said:
so i pulled the whole beast apart again and blasted the volume pot again, this time i have almost gone through the whole can of deoxit, put it back together and it worked great again but for only a few days, and im back to square one now, so when ever i want to use it i have to turn off the speakers and turn the volume up and down a ton just to clear it, is it volume put broken or is it so dirty that im just mushing the dirt around?
Click to expand...

Carbon tracks inside could have got damaged. At this stage you may just have to replace the pot.

Rgds
Mayank
 
Try using the Caig products described in their instruction. I start with a flush of isopropyl alcohol, which helps move out particulate matter. I then use Deoxit D100 followed by Fader F100 and end with Shield.

Deoxit Instructions.jpg
 
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Mayank said:
Carbon tracks inside could have got damaged. At this stage you may just have to replace the pot.

Rgds
Mayank
Click to expand...
But if the track was damaged then why would it start to get better if i turn it up and down a few times, then it works great
 
AE Bob said:
You could have some DC voltage on the potentiometer, usually from a leaky coupling capacitor. It only takes a few milivolts (less than 100 mV) on the pot to make it go noisy again soon after cleaning
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Coupling capacitor? would these capacitors be on the power supply board or near the volume pot?
 
KingBubba said:
Try using the Caig products described in their instruction. I start with a flush of isopropyl alcohol, which helpsView attachment 1963789 move out particular matter. I then use Deoxit D100 followed by Fader F100 and end with Shield.
Click to expand...
With how much a can of deoxit cost me with shipping im busted right now on spending for more sprays and cleaners, im guessing these cans of spray are expensive like deoxit?
 
As you've already used a whole can of DeOxit, that is why I suggested the cheaper option of replacing the pot. The wipers could be making contact on the side of the track when you turn it a few times.
Why not add an external pot temporarily by de-soldering the wires to the original pot to confirm the cause (a) coupling cap or (b) damaged track?

Rgds
Mayank

PS this is how a damaged pot carbon track looks like inside
damaged pot.jpg
 
Mayank said:
As you've already used a whole can of DeOxit, that is why I suggested the cheaper option of replacing the pot. The wipers could be making contact on the side of the track when you turn it a few times.
Why not add an external pot temporarily by de-soldering the wires to the original pot to confirm the cause (a) coupling cap or (b) damaged track?

Rgds
Mayank

PS this is how a damaged pot carbon track looks like inside
View attachment 1963793
Click to expand...
Hopefully this will be a last resort kind of thing, but if i do end up having to replace the whole pot, what do you recommend as a replacement for it?
 
Mayank said:
Do you have the Service Manual?
The volume pot is usually 500K

Rgds
Mayank
Click to expand...
From long around at the 500k pots i see there only for stero, this is a quadraphonic system meaning the p[ots would have 4 parts to solder new wires on, is there anywhere that sells these? cause parts express doesn't appear to :(
 
Ouch. I didn't realize that :eek:

Sourcing a quad 500K potentiometer (also known as 4 gang) will be difficult. Also, you would need to match the shaft length and diameter for the original knob. Surplus stores, eBay perhaps.
Maybe someone else here may know a source.

Good luck.
Mayank

PS eBay has two listings for 100K quad pots (no affiliation with seller):
https://www.ebay.com/itm/2-x-Alpha-...858042?hash=item3ac6d3947a:g:plgAAOxy79JRgpfh
https://www.ebay.com/itm/2-x-ALPS-R...094141?hash=item3b3d64e9fd:g:3d8AAOSwQLZd24wQ
 
If you become a AK subscriber, you can also post on Barter Town (available only to subscribers). Someone may have a replacement.
 
Is the noise in one particular channel? If so I would bet you a cup of coffee, that there is DC on that section. The fact it goes away if you mess with it after turn on is a dead give away. The cap (or caps) are leaky, but eventually they charge and the DC is no longer on the element. Use a multimeter and check the high side of the pot for DC right after turn on, and with the pot turned up some, check the wiper of the pot for DC (backfeeding from the next stage). It doesn't take much to make the pot noisy.(only 0.050 volts or so).
 
Someone could also have used WD40 or similar at some point which destroys carbon tracks. I've had a few like that over the years, contact cleaner fixes it for a day then the noise comes back.
 
DeOxit D-5 will wash out the lubricants on the wafer and the pot, making it feel kind of gritty. If you don't replace the lubricant, your pots can go noisy after the carrier in the DeOxit dries. Get a can of CRC 2-26 electronics lubricant @home depot (about $5. a can). A very short spritz is all it requires.

But having said that, AEBob, and Mayank's comments are valid and quite possible.
 
larryderouin said:
DeOxit D-5 will wash out the lubricants on the wafer and the pot, making it feel kind of gritty. If you don't replace the lubricant, your pots can go noisy after the carrier in the DeOxit dries. Get a can of CRC 2-26 electronics lubricant @home depot (about $5. a can). A very short spritz is all it requires.

But having said that, AEBob, and Mayank's comments are valid and quite possible.
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This seems like the cheapest and easiest thing to try first out of all the suggestions, problem is im in canada and cant seem to find this product,is there any other brands that make this kind of lube that i could search for in canada?

EDIT
What about something like this? https://www.amazon.ca/Gardner-Bende...nt&qid=1598534491&sr=8-1&tag=googcana-20&th=1
 
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AE Bob said:
Is the noise in one particular channel? If so I would bet you a cup of coffee, that there is DC on that section. The fact it goes away if you mess with it after turn on is a dead give away. The cap (or caps) are leaky, but eventually they charge and the DC is no longer on the element. Use a multimeter and check the high side of the pot for DC right after turn on, and with the pot turned up some, check the wiper of the pot for DC (backfeeding from the next stage). It doesn't take much to make the pot noisy.(only 0.050 volts or so).
Click to expand...
It seems to come from the front left and the back right, but i turned the little volume knobs for all 4 speakers to off and then turned the volume pot up and down and i still heard the snapping popping sound coming from those two speakers even though i had there separate volume knobs turned to off, i have a multi meter but in order for me to test it i would need a step by step on how to test and what setting and where to put the probs lol
 
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