Becker volume knob fix - Mercedes-Benz Forum
 
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#1 (permalink) Old 10-02-2011, 08:26 AM
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Becker volume knob fix

I have a 94 wagon that came with a Becker 1492 and it had the problem with the volume knob pot not working correctly. I pulled the unit and discovered that it was a sealed pot so I ordered a Becker 1692 on Ebay that bolted right in as a direct replacement. However, it had the same problem. Here is what I did to my 1692 and to a friend's 1692 in his 97 W210. After about a month they are both still operating perfectly. This will also work on the 1492 and possibly many others.

I used the Deoxit shown in the picture below. I bought this at Guitar center and have great success on cleaning the pots on old stereos, guitars, amps, etc. It cleans and lubes the pot and seems to be a long term fix. It is easy to find on-line.

When you remove the volume knob you will see a shoulder where the post enters the pot. I dug through my junk drawer and found a piece of plastic semi transparent tubing with an ID of 1/4" and an OD of 3/8". The OD was a bit too large to fit through the faceplate so I ground it down a bit as shown in the photo to allow clearance. As I recall I bought this tubing at ACE hardware for an unrelated project.

Once it would fit I pushed it securely onto the shoulder of the pot as shown in the photo. I then inserted the spray nozzle and sprayed a bit of fluid into the tubing until I could see fluid about 3/4'' deep in the bottom of the tube. I used a shop rag wrapped around the top of the tube so fluid wouldn't spray back into the car.

I watched it for a while and could not see any difference in the fluid level in the tube so I put my lips around the tube and blew to create a bit of pressure and sure enough, a few puffs and I could see the fluid level drop as it forced the fluid between the shaft and the shoulder. I then carefully removed the tube by holding my rag on the end and tilting it down and off as to not dump the remaining fluid behind the face plate.

Now I took a 8" section of fuel line that fit snugly on the shaft and used it to work the shaft back and forth to help the Deoxit clean the contacts in the pot. I even ended up chucking the end of the fuel line into a cordless drill and using that to work the shaft back and forth.

So far both pots that I have done this to are both working as new. I hope someone can benefit from this and I appreciate all of the work from others who take the time to post repair info on this forum.

Cheers!
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#2 (permalink) Old 10-02-2011, 09:54 AM
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That's just the fist step with DeoxIt. If you want the repair to last indefinitely, you finish the cleaning/lubricating with DeoxIT Gold G5. All you've done is clean the pot, not restore and lube it. And the cordless drill part is scary, you never work a pot with more than your fingers!

Kevin
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#3 (permalink) Old 10-02-2011, 01:41 PM
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The Deoxit gold would be a good addition but I didn't happen to have any on hand. I certainly wouldn't just spin the hell out of the pot with high speed but the fuel line worked great at low speed and saved me a lot of time over doing it by hand. The point of my thread was that I figured out a way to get electrical cleaner in the pot and it doesn't even require removal of the stereo. The two that I have done have so far operated as new and the fix only took a few minutes. In my experience the Deoxit is my favorite electrical cleaner but this technique could be done with other brands as well. I hope it saves someone the aggravation of disassembling their stereo only to find that the pot is sealed and that the only way to clean it is through the clearance around the shaft.
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#4 (permalink) Old 10-02-2011, 11:13 PM
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I got your original point, really. I was adding that the pot isn't fully restored, just cleaned. I was giving you feedback from the hundreds of vintage stereo equipment pieces I've restored and what works long-term. A pot is a pot and doesn't matter if it's in a car or your home-that was my point.

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#5 (permalink) Old 11-15-2014, 10:17 AM
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Thanks to the OP Goofaroo for the good info!
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#6 (permalink) Old 11-15-2014, 10:28 AM
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Someone mentioned "that a pot is a pot". Well I might be wrong but in this case a Becker pot is NOT a pot but an "encoder". Have no idea how they work but if the spray stuff works, "good on you!"
I will try it on my '95 E420
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#7 (permalink) Old 11-15-2014, 10:42 AM
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Wow! Thank you very much for your post - you have helped me greatly - I am a complete newbie and new to this type of tech forum. This is exactly the same problem I am having with my radio (looks to be the exact same one) in my 1995 Cabriolet - but I didn't know how to fix it. This stereo has tremendous sound and all six speakers appear to work. In my case, the volume knob is extremely sensitive. You can turn is up just slightly, and the volume 'jumps ahead' and blows you out of the car. I suspected it was a dirty pot but did not know how to go about fixing it. Years ago flying Radio Control models, the control servos used to routinely get jittery when the pots and wiper armatures got dirty. Seems like we used alcohol to clean and then used silicone grease to keep them quiet. I have same issue with a Klipsh Sub Woofer too - fortunately it is on a much larger scale so I can get to it. Never would have learned how to fix my MB volume knob or the DeoxIT product.
Thanks again - W124_W126Fan. Located in South Florida.
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#8 (permalink) Old 11-17-2014, 07:51 AM
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agreed, one cannot tell the exact mechanism of the inside of a potentiometer, what materials comprise it, unles one has priore experience dismantling them. Edward Ebel (Becker AutoSound) a professional in these matters and he provided insight into the Becker 1492 construction: see post #9 in prior thread: Becker 1492 volume control knob | Mercedes-Benz Club of America

apparently, the part number is 1155.466-385 Encoder Switch, available from Becker North America. requires some soldering skill to replace.

best,
kenh
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#9 (permalink) Old 11-17-2014, 08:21 AM
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The only other place outside Becker USA that can fix these radios is La Jolla Audio in San Diego.

They repaired one of my radios once for the same issue. See link

San Diego Car Stereo Shop / Audio System / Installation / Bluetooth Hands Free Kit / GPS Navigation / Ipod Install - La Jolla Audio
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