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NAD  model 4150 AM/FM solid state receiver.  

This unit took a hit to the rear and probably exasperated latent factory created problems and became intermittent.  Even though I am not set up for Solid State, I will try to "repair" just about anything once.  You never know if it is something simple like a cold solder joint on some hot component lead needing only a  touched up.  

This is not a restoration but only a "Fix or Repair".  I could not locate any readily available schematic or alignment date.  No alignments were performed. 

    

The case has been cleaned of dirt and shined up with some Glayzit.

 

 

IMG_1958.JPG (134714 bytes) Test setup.  Two surplus powered computer speakers do just fine.   IMG_1959.JPG (524711 bytes)  IMG_1907.JPG (254811 bytes) IMG_1936.JPG (235641 bytes) This unit took a hit.  I will look for cracks in the PC board.  I "formed" and straightened the rear panel.  Remember!  You never  bend anything for a client.  

You are to "FORM" it!

IMG_1934.JPG (138649 bytes) This is a misalignment probably from the hit the unit took.  I removed the front panel for inspection of the display and push-button circuit boards.
IMG_1910.JPG (247377 bytes) Flexing the frame cause the FM to cut in and out. IMG_1932.JPG (470245 bytes)  Yup.  The FM cuts in and out when I flex the frame.  AM seems to be not affected.  So I begin a careful inspection, touching up suspicious solder joints that look anything but perfect.  IMG_1911.JPG (1326455 bytes) While retouching,  I came across this gouge. 

Where it came from?  I do not know.   Perhaps some one was in here before me, perhaps the factory. It's not unheard of.

IMG_1917.JPG (474511 bytes) I scraped off the green coating, widened the insulation gap and put jumpers across any suspected cracked trace areas.  But, no change in the symptoms resulted.  So on with the search.  
IMG_1918.JPG (324385 bytes)Hmmm.  Found something under the coaxial cable jumper from the FM RF section...... IMG_1922.JPG (399269 bytes) This is the unsoldered resistor wire.  It appears to be a load resistor for one of the FM crystal IF filters. IMG_1921.JPG (336560 bytes) The FM receives some what, when I push on this unsoldered wire.  Still intermittent but the sounds of the failure have changed.  IMG_1926.JPG (289305 bytes) Just after finding the unsoldered resistor I found a solder bridge.  Dull from the factory.  Can you see it?  IMG_1926.JPG (70835 bytes) How about now?  It is on the right.  Two deposited solder blobs creating a bridge.  I suspect when I flexed the board it made and broke the connection.  Also heat would cause this to make and break.   I simply disordered then applied fresh solder being a bit careful not to use too much solder. 
IMG_1926c.JPG (66617 bytes) It is circled in Red. Click to enlarge image(s)  

This is the excessive solder and resulting bridge removed.

IMG_1927d.JPG (95540 bytes)

I believe that I have found the root cause of the intermittent FM reception. 

 

Flexing the frame does not kill the FM reception any more.  AM seemed not to be affected.  

IMG_1927.JPG (599775 bytes) The repaired solder areas are dabbed in red for tracking.   IMG_1933.JPG (302185 bytes) After soldering the lead wire I found a solder bead hanging from a thread (of what I don't know).  It is dull and oxidized, so this is likely old and not from my soldering work today. I ran this unit a few hour with out any failures. 

I will continue to run this unit in the shop until it is returned to the owner. 

 

Even today some solid state electronics is collected and appreciated as vintage gear.  The best example (for me) are NIXIE tube displays.     Picture from; http://en.wikipedia.org/wiki/Nixie_tube

 

 

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