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Post by jdubs on Nov 20, 2021 10:00:00 GMT -5
I bought a used Sherbourne amp (4Z-75) from a member here. It's older, but perfect shape. I think it sat for a good bit of time, which I think is contributing to my problem.
It has a crackle with an associated drop of the left channel in the VC at about 9-10 o'clock on the dial. I turned it off and "exercised" the pot and it helped. But it would come right back. I'd exercise it the next day and it came right back. So, I bought an aerosol can of contact cleaner, popped the top off, and sprayed the assembly on the inside, exercised the VC, and could feel it loosen up. It was good for awhile. Now, it's starting to come back again and I can feel a very slight grinding/catch when I exercise it.
Question: does this need professional help? What's my next step?
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Post by jbrunwa on Nov 20, 2021 13:36:48 GMT -5
I bought a used Sherbourne amp (4Z-75) from a member here. It's older, but perfect shape. I think it sat for a good bit of time, which I think is contributing to my problem. It has a crackle with an associated drop of the left channel in the VC at about 9-10 o'clock on the dial. I turned it off and "exercised" the pot and it helped. But it would come right back. I'd exercise it the next day and it came right back. So, I bought an aerosol can of contact cleaner, popped the top off, and sprayed the assembly on the inside, exercised the VC, and could feel it loosen up. It was good for awhile. Now, it's starting to come back again and I can feel a very slight grinding/catch when I exercise it. Question: does this need professional help? What's my next step? I’m not familiar with this amp, but if it is a potentiometer or variable resistor, I have always used Deoxit Fader for potentiometers, as it both cleans and lubricates. Contact cleaner generally removes all lubricant when it cleans, which can give you that grinding feel when the lubricant is washed away, and may even further deteriorate the resistor surface by using it without lubricant. If Deoxit Fader doesn’t fix it, then I replace the potentiometer. If you don’t want to try a new product and have some electrically safe silicone lubricant, you might cleaning again and try a touch of lube. |
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Post by jdubs on Nov 20, 2021 16:32:06 GMT -5
Thanks, I’ll order some of that deoxit. I have others laying around but that seems like a good one to have on hand.
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Post by jbrunwa on Nov 20, 2021 16:41:26 GMT -5
Thanks, I’ll order some of that deoxit. I have others laying around but that seems like a good one to have on hand. You’re welcome. If that doesn’t fix it, replacing a potentiometer can be one of the easiest DIY repairs on older equipment, unless it’s one of those ganged controls where they stacked several potentiometers together.. |
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Post by jdubs on Nov 25, 2021 14:57:13 GMT -5
Sprayed it with the deoxit fader and turned it about 20 times. Turned it on and it seemed fine with no static or dropping out. Any grinding was gone. After listening for awhile I sprayed it and exercised it again while the top was off. Hopefully that took care of it!
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Post by leonski on Nov 25, 2021 23:42:06 GMT -5
This is a COMMODITY part. Nothing exclusive or special about a potentiometer. It'll be some value......20k, 50k or even 100k .....all in 'ohms'. Sherbourne or perhaps Emotiva SHOULD be able to help you with a schematic..... It is also possible to MEASURE the maximum resistance with a simple meter. Your tech should be able to do this in short order. Most likely you want 'audio taper' which is the rate of resistance change per degree of rotation. You have a choice, usually of Linear, Log, or Audio......some 'crossing' of terms here, so check out the link...... Nearly ANY technician who can tell one end of a screwdriver from the other should be capable of this swap without issue. TAKE and post a picture of the part, if you can. It'll either have 3 tabs which solder directly TO a circuit board or 3 wires which go to the same board. Front panel mount type is with a nut/ washer / spacer...... www.hoaglandcustom.com/2017/05/15/hello-world/OR: components101.com/articles/different-types-of-potentiometers-and-how-to-use-themCheck out the pics. |
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Post by jdubs on Nov 26, 2021 11:33:36 GMT -5
It's looking like I DON'T have to change the pot, but if the issue comes back that will be my next option. I'll follow that advice if I do have to.
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Post by leonski on Nov 27, 2021 18:54:01 GMT -5
Just my OPINION, but I'd be proactive and see about a schematic and fina the right part(s) since this kind of problem rarely 'heals itself'.....
Until than? GREAT JOB getting back up and running......
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