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cougarcat 
Member - Posts: 13
Member spacespace
Joined: May 19, 2009
Location: Missouri, United States
Posted: June 09, 2009 at 1:33 AM / IP Logged  
I just picked up a alpine cdm-7874 and installed it in my 88 cougar.When I try to adjust the vol,bass,and trem,its will not respond to make the adjustment  up or down.it just stays on 12.Anyone know the remedy or   what  the problem may be
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: June 09, 2009 at 5:59 AM / IP Logged  

If the volume knob's turning feature seems to not be working, they do go bad.  They are replaceable, and also easily repairable.  Repairable as in you can repair the control you already have.  It will cost you about 5 dollars at a hardware store.  You have to remove the control from the board.  That is the hardest part.  Let me know if you need instructions.

cougarcat 
Member - Posts: 13
Member spacespace
Joined: May 19, 2009
Location: Missouri, United States
Posted: June 09, 2009 at 9:15 PM / IP Logged  
Yes your help is very much needed,I just purchased the faceplate from ebay,and I dont want to mess things up as they are.
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: June 09, 2009 at 10:35 PM / IP Logged  
Using a #00 Phillips screwdriver, remove the screws from the back of the face. Remove the volume knob. Stick your fingernail between the front and back of the face and run it from one end to the other unlocking the tabs. Remove the back cover from the face. There will be some more screws securing the circuit board to the front of the face. Once they are removed, lay the face on a flat surface. Front of the face to remain flat. If it is turned upside down, it will take a while to put all the buttons back where they belong. Locate the volume control and identify the 7 solder points that attach it to the board. There are 2 large connections that hold the pot in place. A solder sucker would be very helpful here. Desoldering braid may be more practical. If you do buy a solder sucker, spend the extra money and get an Edsyn Soldapult. You should be able to get a small one for about 20 dollars. Put some extra solder on all 7 joints. You do not want to heat the control up any more than you have to. Put extra solder on one of the small joints. Then put on one of the larger ones. Allow things to cool down for a minute or 2. Do another small one and then the other larger one. Let cool and then do the rest of the small ones, allowing cooling time between. Now using the solder sucker, heat one of the large connections and suck the solder out of that joint. Once you get the hole pretty clear, press the metal tab toward the middle of the control and suck the solder out again. Let it cool and do the other large connection. Once you are sure that the larger connections are not attached to the board, (you should be able to move the metal tabs with your finger) Now you need to lay your iron across the 2 joints and heat both of them up. When they are hot, keep your iron on them while you rock the 2 pins out of the board by pushing the shaft of the control. Do not push hard on the shaft, once the pins come out it will be easy to bend the other 3 pins. Let it cool and repeat for the 3 pins on the other side. After you get the control out of the board, you can now use the solder sucker to clean the 5 holes.
Bring the control to the hardware store and purchase a pipe nipple that the control fits into easily. 2 inches long will be fine. Purchase 2 PVC pipe caps that will screw onto the nipple. Drill a 1/4 inch hole in one of the caps. Screw the undrilled cap onto the nipple. Drop the control in with shaft up. Fill to slightly above the control (not the shaft) with WD-40. Now screw the drilled cap onto the top of the nipple. With an air compressor and a blow nozzle, pressurize the nipple. You may need to use electrical tape to make a seal on the hole in the cap. A rubber tipped blow nozzle works great. This will force the WD into the sealed pot. Remove the pot and resolder into the board.
As soon as you remove the pot from the nipple, turn the knob back and forth about 20 times, this will clean the contacts further. You should be able to see the much darker than usual WD-40 coming out of the seams.
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: June 09, 2009 at 10:58 PM / IP Logged  
36B50405Y01      KNOB, ROTARY CDM7874      1 TO 2 DAYS*        $8.34        
Pacific Coast Parts can have a new knob to you in about a week. These things used to cost nearly 30 dollars. At 8.34 plus shipping, I would think real hard about getting a new one. pacparts.com 1-800-421-5080

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