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Power amp maintenance...


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Pulled one of my RMX 1850's yesterday to clean a noisy pot and found the shaft was broken. I've got a replacement pot on the way, but it brings up a question: There doesn't seem to be any good way to clean the attenuator pots. They seem to be sealed with no access to spray some cleaner inside. Is there a quick way to clean a noisy pot on these? Also, I was planning to clean the cooling system but there's no filter or anything. I wiped the dust off the fan, and since I had the heat sink out anyway to repair the pot brushed off the heat sink. Anything else that ought to get looked at while I'm in there?

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Mechanical plus they (some) can generate a voltage that can damage variable speed drive or commutating electronics. Without knowing the fan and the electronics, I recommend playing it safe.

 

 

I learned something new. Thanks. Agreed I use compressed air.

 

Someone made a device that was a tube from your can of spray cleaner to a threaded end that threaded down over the shaft where the surface mount nut would go (there were adapters for different size/pitch threads. This obstensibly allowed you to force cleaner down the shaft, into the sealed pot. It worked SOMETIMES and always used a lot of cleaner that blew everywhere (IMO more of a PITA than it was worth). Replacing the pot is your best bet.

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Mechanical plus they (some) can generate a voltage that can damage variable speed drive or commutating electronics. Without knowing the fan and the electronics, I recommend playing it safe.

 

 

I can fully agree with playing it safe, however I have strong doubts that the back EMF would be an issue (unless of course the design was beyond HORRIBLE), not with the inductance and magnetics of a small cooling fan.

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I learned something new. Thanks. Agreed I use compressed air.


Someone made a device that was a tube from your can of spray cleaner to a threaded end that threaded down over the shaft where the surface mount nut would go (there were adapters for different size/pitch threads. This obstensibly allowed you to force cleaner down the shaft, into the sealed pot. It worked SOMETIMES and always used a lot of cleaner that blew everywhere (IMO more of a PITA than it was worth). Replacing the pot is your best bet.

 

 

All that will do is blow the shaft lube into the elemnt and make an even bigger mess IMO.

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I can fully agree with playing it safe, however I have strong doubts that the back EMF would be an issue (unless of course the design was beyond HORRIBLE), not with the inductance and magnetics of a small cooling fan.

 

 

With some designs it certainly can, especially with the speeds the fan can attain when blown with forced air from a compressor. My tech was playing around with this a few years back and hit over 10k RPM this way and while the fan held together it was no longer functional.

 

I'll have to look around and see ifthere's any information on this, my fan vendor confirmed the potential and recommends locking the fan with say a pencil or similar when using compressed air.

 

Here's a little something about the construction and how the back-EMF waveform of some configurations can feed tach controls. The problem is that sppeding the fan up greatly beyond it's design speed generates proportionally higher voltages and the direction of rotation may cause unexpected results with the electronic commutation. http://en.wikipedia.org/wiki/Brushless_DC_electric_motor

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I'm curious how it was tach-ed? Strobe light? Sonically? I've also spun some up pretty well (it takes a special touch to get them to really sing)... I was always curious what mach I'd hit.

 

 

Actually a product that my engineering partner designed for testing engine RPM of free-flight RC models while in flight. Has an acoustic AND optical tach and a program for number of cylinders, 2 or 4 stroks and/or number of prop blades. He was a real rocket scientist in his past life, worked on the Apollo program.

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